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000
FXUS63 KILX 011208
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
708 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 708 AM CDT MON SEP 1 2014

A mix of IFR and MVFR ceilings and southerly winds generally 8-12
kts this morning across central Illinois as a cold front
approaches from the west. A line of thunderstorm activity ahead of
the front continues to approach, however activity is generally weak
along portions of the line headed for central IL. As surface
heating takes place, thunderstorm development will intensify
through the early afternoon as daytime heating initiates and the
most intense portions of the storm system move into the region.
Some storms may become severe with hail and severe wind gusts this
afternoon and evening. Thunderstorm activity will shift toward
southeast portions of the state tonight. As no clear features
exist at this point to pinpoint timing of thunderstorms, have
broad-brushed thunderstorm activity with predominant -SHRA and VCTS
in TAFs starting 16Z- 17Z...then diminished VCTS/VCSH mention from
northwest to southeast overnight. Doubtful MVFR ceilings will
dissipate significantly through the day so have kept cigs no
better than bkn020-025 for the next 24 hours.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON







000
FXUS63 KILX 011208
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
708 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 708 AM CDT MON SEP 1 2014

A mix of IFR and MVFR ceilings and southerly winds generally 8-12
kts this morning across central Illinois as a cold front
approaches from the west. A line of thunderstorm activity ahead of
the front continues to approach, however activity is generally weak
along portions of the line headed for central IL. As surface
heating takes place, thunderstorm development will intensify
through the early afternoon as daytime heating initiates and the
most intense portions of the storm system move into the region.
Some storms may become severe with hail and severe wind gusts this
afternoon and evening. Thunderstorm activity will shift toward
southeast portions of the state tonight. As no clear features
exist at this point to pinpoint timing of thunderstorms, have
broad-brushed thunderstorm activity with predominant -SHRA and VCTS
in TAFs starting 16Z- 17Z...then diminished VCTS/VCSH mention from
northwest to southeast overnight. Doubtful MVFR ceilings will
dissipate significantly through the day so have kept cigs no
better than bkn020-025 for the next 24 hours.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON







000
FXUS63 KILX 011208
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
708 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 708 AM CDT MON SEP 1 2014

A mix of IFR and MVFR ceilings and southerly winds generally 8-12
kts this morning across central Illinois as a cold front
approaches from the west. A line of thunderstorm activity ahead of
the front continues to approach, however activity is generally weak
along portions of the line headed for central IL. As surface
heating takes place, thunderstorm development will intensify
through the early afternoon as daytime heating initiates and the
most intense portions of the storm system move into the region.
Some storms may become severe with hail and severe wind gusts this
afternoon and evening. Thunderstorm activity will shift toward
southeast portions of the state tonight. As no clear features
exist at this point to pinpoint timing of thunderstorms, have
broad-brushed thunderstorm activity with predominant -SHRA and VCTS
in TAFs starting 16Z- 17Z...then diminished VCTS/VCSH mention from
northwest to southeast overnight. Doubtful MVFR ceilings will
dissipate significantly through the day so have kept cigs no
better than bkn020-025 for the next 24 hours.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON







000
FXUS63 KILX 011208
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
708 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 708 AM CDT MON SEP 1 2014

A mix of IFR and MVFR ceilings and southerly winds generally 8-12
kts this morning across central Illinois as a cold front
approaches from the west. A line of thunderstorm activity ahead of
the front continues to approach, however activity is generally weak
along portions of the line headed for central IL. As surface
heating takes place, thunderstorm development will intensify
through the early afternoon as daytime heating initiates and the
most intense portions of the storm system move into the region.
Some storms may become severe with hail and severe wind gusts this
afternoon and evening. Thunderstorm activity will shift toward
southeast portions of the state tonight. As no clear features
exist at this point to pinpoint timing of thunderstorms, have
broad-brushed thunderstorm activity with predominant -SHRA and VCTS
in TAFs starting 16Z- 17Z...then diminished VCTS/VCSH mention from
northwest to southeast overnight. Doubtful MVFR ceilings will
dissipate significantly through the day so have kept cigs no
better than bkn020-025 for the next 24 hours.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON






  [top]

000
FXUS63 KLOT 011138
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 AM CDT MON SEP 1 2014

.DISCUSSION...
340 AM CDT

ENTERING SEPTEMBER AND METEOROLOGICAL AUTUMN WE STILL FIND THE
FORECAST CHALLENGES TO BE MORE SUMMER-LIKE...AT LEAST EARLY ON IN
THE FORECAST. THAT IS STORM AND HEAVY RAIN POTENTIAL TODAY AND
TONIGHT...THEN STORM CHANCES WEDNESDAY NIGHT AND FRIDAY WHICH
SANDWICH A POSSIBLE 90 PLUS DEGREE DAY ON THURSDAY. LESS BUT
STILL SOME TIME WAS SPENT ON THE FINAL CHALLENGE OF HOW MUCH OF A
COOL DOWN OCCURS THE FIRST FULL WEEKEND OF THIS NEW METEOROLOGICAL
SEASON.

SYNOPSIS...
A LONG WAVE TROUGH EXTENDING SOUTHWARD THROUGH CANADA INTO THE NORTH
CENTRAL U.S. HAS A VERY PROGRESSIVE SHORT WAVE FEATURE MOVING
THROUGH ITS SOUTHERN BASE. THIS IS SPEEDING EAST-NORTHEAST ACROSS
IA EARLY THIS MORNING. A SURFACE COLD FRONT MOVING EAST LAGS THIS
SHORT WAVE...EXTENDING FROM NORTHERN MN THROUGH THE TX PANHANDLE
EARLY THIS MORNING...WITH MULTIPLE SURFACE WAVES IN THE 1003MB
NEIGHBORHOOD ALONG IT. NORTHWEST SURFACE FLOW BEHIND THIS FRONT IS
NOT PARTICULARLY STRONG SO THIS FRONT WILL CONTINUE TO BE A SLOW-
MOVER TODAY...NOT EXPECTED TO ENTER THE FORECAST AREA UNTIL THIS
EVE. BEING WITHIN A WARM SECTOR UNDER QUICKENING UPPER/MID-LEVEL
FLOW PRESENTS THE STORM CHANCES THESE 24 HOURS.

THIS MORNING...
A LOOSELY DEFINED MCS MOVING EASTWARD INTO NORTHWEST IL EARLY THIS
MORNING WANED CONSIDERABLY WITH WARMING CLOUD TOPS AND OUTFLOW
EXTENDING WELL AHEAD OF IT. SEEING AN UPTICK ACROSS WEST CENTRAL IL
LIKELY ASSOCIATED WITH LIFT OF THE AFOREMENTIONED PROGRESSIVE SHORT
WAVE. HIGH RESOLUTION MODELS GREATLY VARY ON WHAT WILL HAPPEN EVEN
JUST A FEW HOURS OUT...BUT WOULD EXPECT SYNOPTICALLY TO SEE SOME
CONVECTION EVOLVE INTO THE FORECAST AREA THIS MORNING...POSSIBLY
ONLY THE WESTERN/SOUTHWESTERN AREA BUT STILL CANT RULE OUT SCATTERED
ACTIVITY MOVING EASTWARD THROUGH THE ENTIRE AREA INCLUDING
CHICAGO DURING MID/LATE MORNING. DESPITE A FAIRLY STRONG LOW-LEVEL
JET INTO ANY ACTIVITY...THE CONTINUED BROAD AREA OF STORMS ACROSS
EASTERN KS INTO WEST/SOUTHWEST MO THROUGH EARLY TO MID MORNING
SHOULD LESSEN MOISTURE TRANSPORT AND THUS ABILITY TO REALIZE STEEP
LAPSE RATES ALOFT FOR MORE ROBUST ACTIVITY...AND MAYBE EVEN
THUNDER IN GENERAL NORTH OF INTERSTATE 80.

THIS AFTERNOON AND TONIGHT...
DESPITE THIS BEING IN THE FIRST 12 HOURS OF THE FORECAST...DUE TO
INFLUENCE OF MORNING STORMS AND LARGE MODEL DIFFERENCES...CONFIDENCE
ON SPECIFICS IN THESE PERIODS REMAIN LOW. THERE SHOULD BE SOME
FORM OF OUTFLOW BOUNDARY OR BOUNDARIES FROM MORNING ACTIVITY/CLOUD
COVER THAT LINGER INTO THE FORECAST AREA INTO THE AFTERNOON...MOST
FAVORED SOUTH OF INTERSTATE 80. AS WARMING AND DESTABILIZATION
OCCURS WITH DEW POINTS AROUND 70F...COULD SEE SCATTERED ACTIVITY
DEVELOP NEAR ANY SUCH BOUNDARIES DURING THE MID TO LATE AFTERNOON.
THE SECOND UPPER WAVE ACROSS WESTERN WY THIS MORNING WILL BEGIN TO
APPROACH THE REGION AS WELL BY LATE IN THE DAY...WITH FORCING FROM
THIS POSSIBLY AIDING IN SCATTERED STORM DEVELOPMENT ACROSS MUCH OF
THE REGION. EVEN EARLY THIS MORNING THERE ARE A HANDFUL OF STORMS
ACROSS THE UPPER MIDWEST NOT LINKED TO ANY SPECIFIC SURFACE
FEATURE. INCREASING DEEP LAYER SHEAR OF 35 TO 50 KT WILL SUPPORT
ISOLATED TO SCATTERED SEVERE DISCRETE STORMS IN THE REGION.

WHILE IT REMAINS DIFFICULT TO PINPOINT TIMING...IT WOULD SEEM THE
GREATEST COVERAGE IN REDEVELOPING STORMS THIS EVENING WOULD BE IN
THE SOUTHERN FORECAST AREA WHERE AFOREMENTIONED BOUNDARY MAY OCCUR
AND MODEST SOUTHWEST 850-925MB FLOW AND MOISTURE TRANSPORT
REMAINS. AS THE AREA BECOMES UNDER A RIGHT ENTRANCE REGION TO THE
UPPER JET...DO EXPECT INCREASING ASCENT TONIGHT IN THE REGION FOR
MORE ROBUST CONVECTION AND POTENTIAL SEVERE AND HEAVY RAIN
THREATS. RIGHT NOW A GUIDANCE OVERLAP WOULD INDICATE THE FAR
SOUTHEAST FORECAST AREA IS MOST FAVORED FOR THIS. PRECIPITABLE
WATERS AROUND TWO INCHES AND STORM MOTIONS NEARLY PARALLEL TO THE
UPPER AND MID LEVEL FLOW WILL PRESENT HEAVY RAIN THREATS IN
THE GENERAL CENTRAL TO SOUTHERN IL INTO IN REGIONS...BUT AGAIN AT
THIS TIME CONFIDENCE VARIES ON PLACEMENT. BECAUSE OF THAT WILL
CONTINUE WITH THE HYDROLOGIC OUTLOOK /ESF/ FOR THE AREAS HIT HARD
ON SATURDAY NIGHT WITH HEAVY RAINFALL.

TUESDAY AND WEDNESDAY...
THE FRONT SHOULD CLEAR THE FORECAST AREA SOMETIME TUESDAY MORNING.
WHILE DRY AIR ADVECTION WILL OCCUR...LIMITED CONVERGENCE REMAINS
IN THE SOUTHEAST FORECAST AREA FOR POSSIBLY A STORM OR TWO TUESDAY
BUT IT LOOKS TO BE A LOW CHANCE. TEMPERATURES ONLY COOL SLIGHTLY
AS HIGH PRESSURE QUICKLY MOVES ATOP THE AREA TUESDAY NIGHT AND
THEN EASTWARD.

WEDNESDAY NIGHT THROUGH FRIDAY...
WARM AIR ADVECTION AND A RAPID PRECIPITABLE WATER INCREASE IS
FORECAST WEDNESDAY NIGHT ON ALL GUIDANCE. FEEL THAT MODELS MAY BE
UNDER-DOING THE STORM CHANCES GIVEN FORECAST PROFILES OF STEEPENING
LAPSE RATES WITHIN A RAPIDLY MOISTENING COLUMN...AT LEAST IN THE
WESTERN FORECAST AREA. SO HAVE INCREASED POPS IN THAT AREA. AS FOR
THURSDAY...HAVE GONE DRY IN MANY AREAS COLLABORATING AND
UNDERCUTTING A MODEL BLEND OF POPS. THE SYNOPTIC PATTERN FAVORS A
HOT DAY AND BARRING ANY STRATUS ISSUES WITH WEDNESDAY NIGHTS WARM
AIR ADVECTION AND POSSIBLE PRECIP...SHOULD SEE THE 90 DEGREE MARK
REACHED OR EXCEEDED ACROSS A GOOD PART OF THE FORECAST AREA BASED
ON STRONG SOUTHWEST FLOW AND FORECAST 850MB AND 925MB TEMPERATURES
COMPARED TO CLIMATOLOGY. FOR NOW HAVE KEPT THE NORTH A LITTLE
BELOW THAT WITH THE POSSIBILITY OF MORNING CLOUDS. THE SYSTEM
COLD FRONT IS PRESENTLY FORECAST BY THE EC AND THE GFS TO COME
THROUGH THE AREA SOMETIME ON FRIDAY WHICH WOULD BRING STORM
CHANCES WITH IT...AS WELL AS FLOW TURNING OFF THE LAKE BEHIND ITS
PASSAGE.

BEYOND...
NO CHANGES MADE TO THIS WEEKEND WHERE HIGHS LOOK TO BE AROUND 70
WITH DRY CONDITIONS BEHIND THE AFOREMENTIONED FRONT. HIGH PRESSURE
AROUND 1023MB IS FORECAST BY A BLEND OF GUIDANCE. GIVEN THE 925MB
TEMPERATURES FORECAST IF THAT HIGH IS CENTERED OVER THE FORECAST
AREA SOMETIME SUNDAY OR MONDAY NIGHTS /7TH OR 8TH/...LOWS IN
OUTLYING AREAS WOULD LIKELY BE IN THE 40S.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* PERIOD OF SHRA/TSRA POSSIBLE MID MORNING INTO EARLY AFTERNOON.
* ANOTHER SMALL CHANCE OF OF FEW SHOWERS/STORMS THIS EVENING.
* SHORT 1 TO 2 HOUR PERIOD OF LIGHT EAST-SOUTHEAST WINDS EARLY
  THIS MORNING...BEFORE BECOMING GUSTY OUT OF THE SOUTHWEST LATER
  IN THE MORNING.

KJB

//DISCUSSION...UPDATED 12Z...

CONVECTIVE CHANCES AND TIMING CONTINUE TO BE THE PRIMARY WEATHER
CONCERN AND FOCUS FOR THE AREA TODAY.

THE OVERNIGHT THUNDERSTORM ACTIVITY TO OUR WEST HAS DISSIPATED AS
IT MOVED ACROSS NORTHERN ILLINOIS. HOWEVER...ITS EFFECTS ON THE
SURFACE WINDS AND CIGS REMAIN. AS SUCH...IT APPEARS THAT A SHORT
PERIOD OF LOW MVFR CIGS AND AN EAST-SOUTHEASTERLY WIND COMPONENT
ARE EXPECTED THROUGH AROUND 14 UTC THIS MORNING BEFORE THE WINDS
REVERT BACK OUT OF THE SOUTHWEST AND BECOME A BIT GUSTY BY MID TO
LATE MORNING.

UNCERTAINTY REMAINS SOMEWHAT HIGH IN WHETHER OR NOT ANY CONVECTIVE
ACTIVITY WILL IMPACT THE TERMINALS TODAY. OVERALL IT APPEARS THE
BEST CHANCES IN THE NEAR TERM WILL BE ROUGHLY BETWEEN 16 AND 19
UTC AS A WEATHER DISTURBANCE ACROSS NORTHEASTERN MISSOURI SHIFTS
EASTWARD OVER THE AREA. THIS COULD LEAD TO SOME DEVELOPMENT
NEAR...OR JUST SOUTH OF THE TERMINALS DURING THIS PERIOD.
THEREAFTER...IT ALSO APPEARS THERE MAY BE ANOTHER CHANCE FOR SOME
SCT STORMS THIS EVENING AFTER 23 UTC AS ANOTHER STOUT UPPER LEVEL
DISTURBANCE MOVES OVER NORTHERN ILLINOIS AS A COLD FRONT
APPROACHES. TIMING AT THIS JUNCTURE REMAINS VERY DIFFICULT TO PIN
DOWN...AND THIS WILL NEED TO BE IRONED OUT AS WE GET A BETTER
HANDEL ON TRENDS THROUGH THE DAY. EITHER WAY...THERE WILL LIKELY
BE AREAS OF CONVECTIVE ACTIVITY THIS AFTERNOON AND TONIGHT SOUTH
OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WIND TRENDS.
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY AND SUNDAY...PREDOMINANTLY VFR.

KJB

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 011138
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 AM CDT MON SEP 1 2014

.DISCUSSION...
340 AM CDT

ENTERING SEPTEMBER AND METEOROLOGICAL AUTUMN WE STILL FIND THE
FORECAST CHALLENGES TO BE MORE SUMMER-LIKE...AT LEAST EARLY ON IN
THE FORECAST. THAT IS STORM AND HEAVY RAIN POTENTIAL TODAY AND
TONIGHT...THEN STORM CHANCES WEDNESDAY NIGHT AND FRIDAY WHICH
SANDWICH A POSSIBLE 90 PLUS DEGREE DAY ON THURSDAY. LESS BUT
STILL SOME TIME WAS SPENT ON THE FINAL CHALLENGE OF HOW MUCH OF A
COOL DOWN OCCURS THE FIRST FULL WEEKEND OF THIS NEW METEOROLOGICAL
SEASON.

SYNOPSIS...
A LONG WAVE TROUGH EXTENDING SOUTHWARD THROUGH CANADA INTO THE NORTH
CENTRAL U.S. HAS A VERY PROGRESSIVE SHORT WAVE FEATURE MOVING
THROUGH ITS SOUTHERN BASE. THIS IS SPEEDING EAST-NORTHEAST ACROSS
IA EARLY THIS MORNING. A SURFACE COLD FRONT MOVING EAST LAGS THIS
SHORT WAVE...EXTENDING FROM NORTHERN MN THROUGH THE TX PANHANDLE
EARLY THIS MORNING...WITH MULTIPLE SURFACE WAVES IN THE 1003MB
NEIGHBORHOOD ALONG IT. NORTHWEST SURFACE FLOW BEHIND THIS FRONT IS
NOT PARTICULARLY STRONG SO THIS FRONT WILL CONTINUE TO BE A SLOW-
MOVER TODAY...NOT EXPECTED TO ENTER THE FORECAST AREA UNTIL THIS
EVE. BEING WITHIN A WARM SECTOR UNDER QUICKENING UPPER/MID-LEVEL
FLOW PRESENTS THE STORM CHANCES THESE 24 HOURS.

THIS MORNING...
A LOOSELY DEFINED MCS MOVING EASTWARD INTO NORTHWEST IL EARLY THIS
MORNING WANED CONSIDERABLY WITH WARMING CLOUD TOPS AND OUTFLOW
EXTENDING WELL AHEAD OF IT. SEEING AN UPTICK ACROSS WEST CENTRAL IL
LIKELY ASSOCIATED WITH LIFT OF THE AFOREMENTIONED PROGRESSIVE SHORT
WAVE. HIGH RESOLUTION MODELS GREATLY VARY ON WHAT WILL HAPPEN EVEN
JUST A FEW HOURS OUT...BUT WOULD EXPECT SYNOPTICALLY TO SEE SOME
CONVECTION EVOLVE INTO THE FORECAST AREA THIS MORNING...POSSIBLY
ONLY THE WESTERN/SOUTHWESTERN AREA BUT STILL CANT RULE OUT SCATTERED
ACTIVITY MOVING EASTWARD THROUGH THE ENTIRE AREA INCLUDING
CHICAGO DURING MID/LATE MORNING. DESPITE A FAIRLY STRONG LOW-LEVEL
JET INTO ANY ACTIVITY...THE CONTINUED BROAD AREA OF STORMS ACROSS
EASTERN KS INTO WEST/SOUTHWEST MO THROUGH EARLY TO MID MORNING
SHOULD LESSEN MOISTURE TRANSPORT AND THUS ABILITY TO REALIZE STEEP
LAPSE RATES ALOFT FOR MORE ROBUST ACTIVITY...AND MAYBE EVEN
THUNDER IN GENERAL NORTH OF INTERSTATE 80.

THIS AFTERNOON AND TONIGHT...
DESPITE THIS BEING IN THE FIRST 12 HOURS OF THE FORECAST...DUE TO
INFLUENCE OF MORNING STORMS AND LARGE MODEL DIFFERENCES...CONFIDENCE
ON SPECIFICS IN THESE PERIODS REMAIN LOW. THERE SHOULD BE SOME
FORM OF OUTFLOW BOUNDARY OR BOUNDARIES FROM MORNING ACTIVITY/CLOUD
COVER THAT LINGER INTO THE FORECAST AREA INTO THE AFTERNOON...MOST
FAVORED SOUTH OF INTERSTATE 80. AS WARMING AND DESTABILIZATION
OCCURS WITH DEW POINTS AROUND 70F...COULD SEE SCATTERED ACTIVITY
DEVELOP NEAR ANY SUCH BOUNDARIES DURING THE MID TO LATE AFTERNOON.
THE SECOND UPPER WAVE ACROSS WESTERN WY THIS MORNING WILL BEGIN TO
APPROACH THE REGION AS WELL BY LATE IN THE DAY...WITH FORCING FROM
THIS POSSIBLY AIDING IN SCATTERED STORM DEVELOPMENT ACROSS MUCH OF
THE REGION. EVEN EARLY THIS MORNING THERE ARE A HANDFUL OF STORMS
ACROSS THE UPPER MIDWEST NOT LINKED TO ANY SPECIFIC SURFACE
FEATURE. INCREASING DEEP LAYER SHEAR OF 35 TO 50 KT WILL SUPPORT
ISOLATED TO SCATTERED SEVERE DISCRETE STORMS IN THE REGION.

WHILE IT REMAINS DIFFICULT TO PINPOINT TIMING...IT WOULD SEEM THE
GREATEST COVERAGE IN REDEVELOPING STORMS THIS EVENING WOULD BE IN
THE SOUTHERN FORECAST AREA WHERE AFOREMENTIONED BOUNDARY MAY OCCUR
AND MODEST SOUTHWEST 850-925MB FLOW AND MOISTURE TRANSPORT
REMAINS. AS THE AREA BECOMES UNDER A RIGHT ENTRANCE REGION TO THE
UPPER JET...DO EXPECT INCREASING ASCENT TONIGHT IN THE REGION FOR
MORE ROBUST CONVECTION AND POTENTIAL SEVERE AND HEAVY RAIN
THREATS. RIGHT NOW A GUIDANCE OVERLAP WOULD INDICATE THE FAR
SOUTHEAST FORECAST AREA IS MOST FAVORED FOR THIS. PRECIPITABLE
WATERS AROUND TWO INCHES AND STORM MOTIONS NEARLY PARALLEL TO THE
UPPER AND MID LEVEL FLOW WILL PRESENT HEAVY RAIN THREATS IN
THE GENERAL CENTRAL TO SOUTHERN IL INTO IN REGIONS...BUT AGAIN AT
THIS TIME CONFIDENCE VARIES ON PLACEMENT. BECAUSE OF THAT WILL
CONTINUE WITH THE HYDROLOGIC OUTLOOK /ESF/ FOR THE AREAS HIT HARD
ON SATURDAY NIGHT WITH HEAVY RAINFALL.

TUESDAY AND WEDNESDAY...
THE FRONT SHOULD CLEAR THE FORECAST AREA SOMETIME TUESDAY MORNING.
WHILE DRY AIR ADVECTION WILL OCCUR...LIMITED CONVERGENCE REMAINS
IN THE SOUTHEAST FORECAST AREA FOR POSSIBLY A STORM OR TWO TUESDAY
BUT IT LOOKS TO BE A LOW CHANCE. TEMPERATURES ONLY COOL SLIGHTLY
AS HIGH PRESSURE QUICKLY MOVES ATOP THE AREA TUESDAY NIGHT AND
THEN EASTWARD.

WEDNESDAY NIGHT THROUGH FRIDAY...
WARM AIR ADVECTION AND A RAPID PRECIPITABLE WATER INCREASE IS
FORECAST WEDNESDAY NIGHT ON ALL GUIDANCE. FEEL THAT MODELS MAY BE
UNDER-DOING THE STORM CHANCES GIVEN FORECAST PROFILES OF STEEPENING
LAPSE RATES WITHIN A RAPIDLY MOISTENING COLUMN...AT LEAST IN THE
WESTERN FORECAST AREA. SO HAVE INCREASED POPS IN THAT AREA. AS FOR
THURSDAY...HAVE GONE DRY IN MANY AREAS COLLABORATING AND
UNDERCUTTING A MODEL BLEND OF POPS. THE SYNOPTIC PATTERN FAVORS A
HOT DAY AND BARRING ANY STRATUS ISSUES WITH WEDNESDAY NIGHTS WARM
AIR ADVECTION AND POSSIBLE PRECIP...SHOULD SEE THE 90 DEGREE MARK
REACHED OR EXCEEDED ACROSS A GOOD PART OF THE FORECAST AREA BASED
ON STRONG SOUTHWEST FLOW AND FORECAST 850MB AND 925MB TEMPERATURES
COMPARED TO CLIMATOLOGY. FOR NOW HAVE KEPT THE NORTH A LITTLE
BELOW THAT WITH THE POSSIBILITY OF MORNING CLOUDS. THE SYSTEM
COLD FRONT IS PRESENTLY FORECAST BY THE EC AND THE GFS TO COME
THROUGH THE AREA SOMETIME ON FRIDAY WHICH WOULD BRING STORM
CHANCES WITH IT...AS WELL AS FLOW TURNING OFF THE LAKE BEHIND ITS
PASSAGE.

BEYOND...
NO CHANGES MADE TO THIS WEEKEND WHERE HIGHS LOOK TO BE AROUND 70
WITH DRY CONDITIONS BEHIND THE AFOREMENTIONED FRONT. HIGH PRESSURE
AROUND 1023MB IS FORECAST BY A BLEND OF GUIDANCE. GIVEN THE 925MB
TEMPERATURES FORECAST IF THAT HIGH IS CENTERED OVER THE FORECAST
AREA SOMETIME SUNDAY OR MONDAY NIGHTS /7TH OR 8TH/...LOWS IN
OUTLYING AREAS WOULD LIKELY BE IN THE 40S.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* PERIOD OF SHRA/TSRA POSSIBLE MID MORNING INTO EARLY AFTERNOON.
* ANOTHER SMALL CHANCE OF OF FEW SHOWERS/STORMS THIS EVENING.
* SHORT 1 TO 2 HOUR PERIOD OF LIGHT EAST-SOUTHEAST WINDS EARLY
  THIS MORNING...BEFORE BECOMING GUSTY OUT OF THE SOUTHWEST LATER
  IN THE MORNING.

KJB

//DISCUSSION...UPDATED 12Z...

CONVECTIVE CHANCES AND TIMING CONTINUE TO BE THE PRIMARY WEATHER
CONCERN AND FOCUS FOR THE AREA TODAY.

THE OVERNIGHT THUNDERSTORM ACTIVITY TO OUR WEST HAS DISSIPATED AS
IT MOVED ACROSS NORTHERN ILLINOIS. HOWEVER...ITS EFFECTS ON THE
SURFACE WINDS AND CIGS REMAIN. AS SUCH...IT APPEARS THAT A SHORT
PERIOD OF LOW MVFR CIGS AND AN EAST-SOUTHEASTERLY WIND COMPONENT
ARE EXPECTED THROUGH AROUND 14 UTC THIS MORNING BEFORE THE WINDS
REVERT BACK OUT OF THE SOUTHWEST AND BECOME A BIT GUSTY BY MID TO
LATE MORNING.

UNCERTAINTY REMAINS SOMEWHAT HIGH IN WHETHER OR NOT ANY CONVECTIVE
ACTIVITY WILL IMPACT THE TERMINALS TODAY. OVERALL IT APPEARS THE
BEST CHANCES IN THE NEAR TERM WILL BE ROUGHLY BETWEEN 16 AND 19
UTC AS A WEATHER DISTURBANCE ACROSS NORTHEASTERN MISSOURI SHIFTS
EASTWARD OVER THE AREA. THIS COULD LEAD TO SOME DEVELOPMENT
NEAR...OR JUST SOUTH OF THE TERMINALS DURING THIS PERIOD.
THEREAFTER...IT ALSO APPEARS THERE MAY BE ANOTHER CHANCE FOR SOME
SCT STORMS THIS EVENING AFTER 23 UTC AS ANOTHER STOUT UPPER LEVEL
DISTURBANCE MOVES OVER NORTHERN ILLINOIS AS A COLD FRONT
APPROACHES. TIMING AT THIS JUNCTURE REMAINS VERY DIFFICULT TO PIN
DOWN...AND THIS WILL NEED TO BE IRONED OUT AS WE GET A BETTER
HANDEL ON TRENDS THROUGH THE DAY. EITHER WAY...THERE WILL LIKELY
BE AREAS OF CONVECTIVE ACTIVITY THIS AFTERNOON AND TONIGHT SOUTH
OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WIND TRENDS.
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY AND SUNDAY...PREDOMINANTLY VFR.

KJB

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT MON SEP 1 2014

.DISCUSSION...
340 AM CDT

ENTERING SEPTEMBER AND METEOROLOGICAL AUTUMN WE STILL FIND THE
FORECAST CHALLENGES TO BE MORE SUMMER-LIKE...AT LEAST EARLY ON IN
THE FORECAST. THAT IS STORM AND HEAVY RAIN POTENTIAL TODAY AND
TONIGHT...THEN STORM CHANCES WEDNESDAY NIGHT AND FRIDAY WHICH
SANDWICH A POSSIBLE 90 PLUS DEGREE DAY ON THURSDAY. LESS BUT
STILL SOME TIME WAS SPENT ON THE FINAL CHALLENGE OF HOW MUCH OF A
COOL DOWN OCCURS THE FIRST FULL WEEKEND OF THIS NEW METEOROLOGICAL
SEASON.

SYNOPSIS...
A LONG WAVE TROUGH EXTENDING SOUTHWARD THROUGH CANADA INTO THE NORTH
CENTRAL U.S. HAS A VERY PROGRESSIVE SHORT WAVE FEATURE MOVING
THROUGH ITS SOUTHERN BASE. THIS IS SPEEDING EAST-NORTHEAST ACROSS
IA EARLY THIS MORNING. A SURFACE COLD FRONT MOVING EAST LAGS THIS
SHORT WAVE...EXTENDING FROM NORTHERN MN THROUGH THE TX PANHANDLE
EARLY THIS MORNING...WITH MULTIPLE SURFACE WAVES IN THE 1003MB
NEIGHBORHOOD ALONG IT. NORTHWEST SURFACE FLOW BEHIND THIS FRONT IS
NOT PARTICULARLY STRONG SO THIS FRONT WILL CONTINUE TO BE A SLOW-
MOVER TODAY...NOT EXPECTED TO ENTER THE FORECAST AREA UNTIL THIS
EVE. BEING WITHIN A WARM SECTOR UNDER QUICKENING UPPER/MID-LEVEL
FLOW PRESENTS THE STORM CHANCES THESE 24 HOURS.

THIS MORNING...
A LOOSELY DEFINED MCS MOVING EASTWARD INTO NORTHWEST IL EARLY THIS
MORNING WANED CONSIDERABLY WITH WARMING CLOUD TOPS AND OUTFLOW
EXTENDING WELL AHEAD OF IT. SEEING AN UPTICK ACROSS WEST CENTRAL IL
LIKELY ASSOCIATED WITH LIFT OF THE AFOREMENTIONED PROGRESSIVE SHORT
WAVE. HIGH RESOLUTION MODELS GREATLY VARY ON WHAT WILL HAPPEN EVEN
JUST A FEW HOURS OUT...BUT WOULD EXPECT SYNOPTICALLY TO SEE SOME
CONVECTION EVOLVE INTO THE FORECAST AREA THIS MORNING...POSSIBLY
ONLY THE WESTERN/SOUTHWESTERN AREA BUT STILL CANT RULE OUT SCATTERED
ACTIVITY MOVING EASTWARD THROUGH THE ENTIRE AREA INCLUDING
CHICAGO DURING MID/LATE MORNING. DESPITE A FAIRLY STRONG LOW-LEVEL
JET INTO ANY ACTIVITY...THE CONTINUED BROAD AREA OF STORMS ACROSS
EASTERN KS INTO WEST/SOUTHWEST MO THROUGH EARLY TO MID MORNING
SHOULD LESSEN MOISTURE TRANSPORT AND THUS ABILITY TO REALIZE STEEP
LAPSE RATES ALOFT FOR MORE ROBUST ACTIVITY...AND MAYBE EVEN
THUNDER IN GENERAL NORTH OF INTERSTATE 80.

THIS AFTERNOON AND TONIGHT...
DESPITE THIS BEING IN THE FIRST 12 HOURS OF THE FORECAST...DUE TO
INFLUENCE OF MORNING STORMS AND LARGE MODEL DIFFERENCES...CONFIDENCE
ON SPECIFICS IN THESE PERIODS REMAIN LOW. THERE SHOULD BE SOME
FORM OF OUTFLOW BOUNDARY OR BOUNDARIES FROM MORNING ACTIVITY/CLOUD
COVER THAT LINGER INTO THE FORECAST AREA INTO THE AFTERNOON...MOST
FAVORED SOUTH OF INTERSTATE 80. AS WARMING AND DESTABILIZATION
OCCURS WITH DEW POINTS AROUND 70F...COULD SEE SCATTERED ACTIVITY
DEVELOP NEAR ANY SUCH BOUNDARIES DURING THE MID TO LATE AFTERNOON.
THE SECOND UPPER WAVE ACROSS WESTERN WY THIS MORNING WILL BEGIN TO
APPROACH THE REGION AS WELL BY LATE IN THE DAY...WITH FORCING FROM
THIS POSSIBLY AIDING IN SCATTERED STORM DEVELOPMENT ACROSS MUCH OF
THE REGION. EVEN EARLY THIS MORNING THERE ARE A HANDFUL OF STORMS
ACROSS THE UPPER MIDWEST NOT LINKED TO ANY SPECIFIC SURFACE
FEATURE. INCREASING DEEP LAYER SHEAR OF 35 TO 50 KT WILL SUPPORT
ISOLATED TO SCATTERED SEVERE DISCRETE STORMS IN THE REGION.

WHILE IT REMAINS DIFFICULT TO PINPOINT TIMING...IT WOULD SEEM THE
GREATEST COVERAGE IN REDEVELOPING STORMS THIS EVENING WOULD BE IN
THE SOUTHERN FORECAST AREA WHERE AFOREMENTIONED BOUNDARY MAY OCCUR
AND MODEST SOUTHWEST 850-925MB FLOW AND MOISTURE TRANSPORT
REMAINS. AS THE AREA BECOMES UNDER A RIGHT ENTRANCE REGION TO THE
UPPER JET...DO EXPECT INCREASING ASCENT TONIGHT IN THE REGION FOR
MORE ROBUST CONVECTION AND POTENTIAL SEVERE AND HEAVY RAIN
THREATS. RIGHT NOW A GUIDANCE OVERLAP WOULD INDICATE THE FAR
SOUTHEAST FORECAST AREA IS MOST FAVORED FOR THIS. PRECIPITABLE
WATERS AROUND TWO INCHES AND STORM MOTIONS NEARLY PARALLEL TO THE
UPPER AND MID LEVEL FLOW WILL PRESENT HEAVY RAIN THREATS IN
THE GENERAL CENTRAL TO SOUTHERN IL INTO IN REGIONS...BUT AGAIN AT
THIS TIME CONFIDENCE VARIES ON PLACEMENT. BECAUSE OF THAT WILL
CONTINUE WITH THE HYDROLOGIC OUTLOOK /ESF/ FOR THE AREAS HIT HARD
ON SATURDAY NIGHT WITH HEAVY RAINFALL.

TUESDAY AND WEDNESDAY...
THE FRONT SHOULD CLEAR THE FORECAST AREA SOMETIME TUESDAY MORNING.
WHILE DRY AIR ADVECTION WILL OCCUR...LIMITED CONVERGENCE REMAINS
IN THE SOUTHEAST FORECAST AREA FOR POSSIBLY A STORM OR TWO TUESDAY
BUT IT LOOKS TO BE A LOW CHANCE. TEMPERATURES ONLY COOL SLIGHTLY
AS HIGH PRESSURE QUICKLY MOVES ATOP THE AREA TUESDAY NIGHT AND
THEN EASTWARD.

WEDNESDAY NIGHT THROUGH FRIDAY...
WARM AIR ADVECTION AND A RAPID PRECIPITABLE WATER INCREASE IS
FORECAST WEDNESDAY NIGHT ON ALL GUIDANCE. FEEL THAT MODELS MAY BE
UNDER-DOING THE STORM CHANCES GIVEN FORECAST PROFILES OF STEEPENING
LAPSE RATES WITHIN A RAPIDLY MOISTENING COLUMN...AT LEAST IN THE
WESTERN FORECAST AREA. SO HAVE INCREASED POPS IN THAT AREA. AS FOR
THURSDAY...HAVE GONE DRY IN MANY AREAS COLLABORATING AND
UNDERCUTTING A MODEL BLEND OF POPS. THE SYNOPTIC PATTERN FAVORS A
HOT DAY AND BARRING ANY STRATUS ISSUES WITH WEDNESDAY NIGHTS WARM
AIR ADVECTION AND POSSIBLE PRECIP...SHOULD SEE THE 90 DEGREE MARK
REACHED OR EXCEEDED ACROSS A GOOD PART OF THE FORECAST AREA BASED
ON STRONG SOUTHWEST FLOW AND FORECAST 850MB AND 925MB TEMPERATURES
COMPARED TO CLIMATOLOGY. FOR NOW HAVE KEPT THE NORTH A LITTLE
BELOW THAT WITH THE POSSIBILITY OF MORNING CLOUDS. THE SYSTEM
COLD FRONT IS PRESENTLY FORECAST BY THE EC AND THE GFS TO COME
THROUGH THE AREA SOMETIME ON FRIDAY WHICH WOULD BRING STORM
CHANCES WITH IT...AS WELL AS FLOW TURNING OFF THE LAKE BEHIND ITS
PASSAGE.

BEYOND...
NO CHANGES MADE TO THIS WEEKEND WHERE HIGHS LOOK TO BE AROUND 70
WITH DRY CONDITIONS BEHIND THE AFOREMENTIONED FRONT. HIGH PRESSURE
AROUND 1023MB IS FORECAST BY A BLEND OF GUIDANCE. GIVEN THE 925MB
TEMPERATURES FORECAST IF THAT HIGH IS CENTERED OVER THE FORECAST
AREA SOMETIME SUNDAY OR MONDAY NIGHTS /7TH OR 8TH/...LOWS IN
OUTLYING AREAS WOULD LIKELY BE IN THE 40S.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT MON SEP 1 2014

.DISCUSSION...
340 AM CDT

ENTERING SEPTEMBER AND METEOROLOGICAL AUTUMN WE STILL FIND THE
FORECAST CHALLENGES TO BE MORE SUMMER-LIKE...AT LEAST EARLY ON IN
THE FORECAST. THAT IS STORM AND HEAVY RAIN POTENTIAL TODAY AND
TONIGHT...THEN STORM CHANCES WEDNESDAY NIGHT AND FRIDAY WHICH
SANDWICH A POSSIBLE 90 PLUS DEGREE DAY ON THURSDAY. LESS BUT
STILL SOME TIME WAS SPENT ON THE FINAL CHALLENGE OF HOW MUCH OF A
COOL DOWN OCCURS THE FIRST FULL WEEKEND OF THIS NEW METEOROLOGICAL
SEASON.

SYNOPSIS...
A LONG WAVE TROUGH EXTENDING SOUTHWARD THROUGH CANADA INTO THE NORTH
CENTRAL U.S. HAS A VERY PROGRESSIVE SHORT WAVE FEATURE MOVING
THROUGH ITS SOUTHERN BASE. THIS IS SPEEDING EAST-NORTHEAST ACROSS
IA EARLY THIS MORNING. A SURFACE COLD FRONT MOVING EAST LAGS THIS
SHORT WAVE...EXTENDING FROM NORTHERN MN THROUGH THE TX PANHANDLE
EARLY THIS MORNING...WITH MULTIPLE SURFACE WAVES IN THE 1003MB
NEIGHBORHOOD ALONG IT. NORTHWEST SURFACE FLOW BEHIND THIS FRONT IS
NOT PARTICULARLY STRONG SO THIS FRONT WILL CONTINUE TO BE A SLOW-
MOVER TODAY...NOT EXPECTED TO ENTER THE FORECAST AREA UNTIL THIS
EVE. BEING WITHIN A WARM SECTOR UNDER QUICKENING UPPER/MID-LEVEL
FLOW PRESENTS THE STORM CHANCES THESE 24 HOURS.

THIS MORNING...
A LOOSELY DEFINED MCS MOVING EASTWARD INTO NORTHWEST IL EARLY THIS
MORNING WANED CONSIDERABLY WITH WARMING CLOUD TOPS AND OUTFLOW
EXTENDING WELL AHEAD OF IT. SEEING AN UPTICK ACROSS WEST CENTRAL IL
LIKELY ASSOCIATED WITH LIFT OF THE AFOREMENTIONED PROGRESSIVE SHORT
WAVE. HIGH RESOLUTION MODELS GREATLY VARY ON WHAT WILL HAPPEN EVEN
JUST A FEW HOURS OUT...BUT WOULD EXPECT SYNOPTICALLY TO SEE SOME
CONVECTION EVOLVE INTO THE FORECAST AREA THIS MORNING...POSSIBLY
ONLY THE WESTERN/SOUTHWESTERN AREA BUT STILL CANT RULE OUT SCATTERED
ACTIVITY MOVING EASTWARD THROUGH THE ENTIRE AREA INCLUDING
CHICAGO DURING MID/LATE MORNING. DESPITE A FAIRLY STRONG LOW-LEVEL
JET INTO ANY ACTIVITY...THE CONTINUED BROAD AREA OF STORMS ACROSS
EASTERN KS INTO WEST/SOUTHWEST MO THROUGH EARLY TO MID MORNING
SHOULD LESSEN MOISTURE TRANSPORT AND THUS ABILITY TO REALIZE STEEP
LAPSE RATES ALOFT FOR MORE ROBUST ACTIVITY...AND MAYBE EVEN
THUNDER IN GENERAL NORTH OF INTERSTATE 80.

THIS AFTERNOON AND TONIGHT...
DESPITE THIS BEING IN THE FIRST 12 HOURS OF THE FORECAST...DUE TO
INFLUENCE OF MORNING STORMS AND LARGE MODEL DIFFERENCES...CONFIDENCE
ON SPECIFICS IN THESE PERIODS REMAIN LOW. THERE SHOULD BE SOME
FORM OF OUTFLOW BOUNDARY OR BOUNDARIES FROM MORNING ACTIVITY/CLOUD
COVER THAT LINGER INTO THE FORECAST AREA INTO THE AFTERNOON...MOST
FAVORED SOUTH OF INTERSTATE 80. AS WARMING AND DESTABILIZATION
OCCURS WITH DEW POINTS AROUND 70F...COULD SEE SCATTERED ACTIVITY
DEVELOP NEAR ANY SUCH BOUNDARIES DURING THE MID TO LATE AFTERNOON.
THE SECOND UPPER WAVE ACROSS WESTERN WY THIS MORNING WILL BEGIN TO
APPROACH THE REGION AS WELL BY LATE IN THE DAY...WITH FORCING FROM
THIS POSSIBLY AIDING IN SCATTERED STORM DEVELOPMENT ACROSS MUCH OF
THE REGION. EVEN EARLY THIS MORNING THERE ARE A HANDFUL OF STORMS
ACROSS THE UPPER MIDWEST NOT LINKED TO ANY SPECIFIC SURFACE
FEATURE. INCREASING DEEP LAYER SHEAR OF 35 TO 50 KT WILL SUPPORT
ISOLATED TO SCATTERED SEVERE DISCRETE STORMS IN THE REGION.

WHILE IT REMAINS DIFFICULT TO PINPOINT TIMING...IT WOULD SEEM THE
GREATEST COVERAGE IN REDEVELOPING STORMS THIS EVENING WOULD BE IN
THE SOUTHERN FORECAST AREA WHERE AFOREMENTIONED BOUNDARY MAY OCCUR
AND MODEST SOUTHWEST 850-925MB FLOW AND MOISTURE TRANSPORT
REMAINS. AS THE AREA BECOMES UNDER A RIGHT ENTRANCE REGION TO THE
UPPER JET...DO EXPECT INCREASING ASCENT TONIGHT IN THE REGION FOR
MORE ROBUST CONVECTION AND POTENTIAL SEVERE AND HEAVY RAIN
THREATS. RIGHT NOW A GUIDANCE OVERLAP WOULD INDICATE THE FAR
SOUTHEAST FORECAST AREA IS MOST FAVORED FOR THIS. PRECIPITABLE
WATERS AROUND TWO INCHES AND STORM MOTIONS NEARLY PARALLEL TO THE
UPPER AND MID LEVEL FLOW WILL PRESENT HEAVY RAIN THREATS IN
THE GENERAL CENTRAL TO SOUTHERN IL INTO IN REGIONS...BUT AGAIN AT
THIS TIME CONFIDENCE VARIES ON PLACEMENT. BECAUSE OF THAT WILL
CONTINUE WITH THE HYDROLOGIC OUTLOOK /ESF/ FOR THE AREAS HIT HARD
ON SATURDAY NIGHT WITH HEAVY RAINFALL.

TUESDAY AND WEDNESDAY...
THE FRONT SHOULD CLEAR THE FORECAST AREA SOMETIME TUESDAY MORNING.
WHILE DRY AIR ADVECTION WILL OCCUR...LIMITED CONVERGENCE REMAINS
IN THE SOUTHEAST FORECAST AREA FOR POSSIBLY A STORM OR TWO TUESDAY
BUT IT LOOKS TO BE A LOW CHANCE. TEMPERATURES ONLY COOL SLIGHTLY
AS HIGH PRESSURE QUICKLY MOVES ATOP THE AREA TUESDAY NIGHT AND
THEN EASTWARD.

WEDNESDAY NIGHT THROUGH FRIDAY...
WARM AIR ADVECTION AND A RAPID PRECIPITABLE WATER INCREASE IS
FORECAST WEDNESDAY NIGHT ON ALL GUIDANCE. FEEL THAT MODELS MAY BE
UNDER-DOING THE STORM CHANCES GIVEN FORECAST PROFILES OF STEEPENING
LAPSE RATES WITHIN A RAPIDLY MOISTENING COLUMN...AT LEAST IN THE
WESTERN FORECAST AREA. SO HAVE INCREASED POPS IN THAT AREA. AS FOR
THURSDAY...HAVE GONE DRY IN MANY AREAS COLLABORATING AND
UNDERCUTTING A MODEL BLEND OF POPS. THE SYNOPTIC PATTERN FAVORS A
HOT DAY AND BARRING ANY STRATUS ISSUES WITH WEDNESDAY NIGHTS WARM
AIR ADVECTION AND POSSIBLE PRECIP...SHOULD SEE THE 90 DEGREE MARK
REACHED OR EXCEEDED ACROSS A GOOD PART OF THE FORECAST AREA BASED
ON STRONG SOUTHWEST FLOW AND FORECAST 850MB AND 925MB TEMPERATURES
COMPARED TO CLIMATOLOGY. FOR NOW HAVE KEPT THE NORTH A LITTLE
BELOW THAT WITH THE POSSIBILITY OF MORNING CLOUDS. THE SYSTEM
COLD FRONT IS PRESENTLY FORECAST BY THE EC AND THE GFS TO COME
THROUGH THE AREA SOMETIME ON FRIDAY WHICH WOULD BRING STORM
CHANCES WITH IT...AS WELL AS FLOW TURNING OFF THE LAKE BEHIND ITS
PASSAGE.

BEYOND...
NO CHANGES MADE TO THIS WEEKEND WHERE HIGHS LOOK TO BE AROUND 70
WITH DRY CONDITIONS BEHIND THE AFOREMENTIONED FRONT. HIGH PRESSURE
AROUND 1023MB IS FORECAST BY A BLEND OF GUIDANCE. GIVEN THE 925MB
TEMPERATURES FORECAST IF THAT HIGH IS CENTERED OVER THE FORECAST
AREA SOMETIME SUNDAY OR MONDAY NIGHTS /7TH OR 8TH/...LOWS IN
OUTLYING AREAS WOULD LIKELY BE IN THE 40S.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 010859
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
359 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK







000
FXUS63 KILX 010859
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
359 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK







000
FXUS63 KILX 010859
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
359 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK







000
FXUS63 KILX 010859
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
359 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CDT MON SEP 1 2014

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense lines...one
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 355 AM CDT MON SEP 1 2014

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed
night.

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK







000
FXUS63 KLOT 010842
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
342 AM CDT MON SEP 1 2014

.DISCUSSION...
340 AM CDT

ENTERING SEPTEMBER AND METEOROLOGICAL AUTUMN WE STILL FIND THE
FORECAST CHALLENGES TO BE MORE SUMMER-LIKE...AT LEAST EARLY ON IN
THE FORECAST. THAT IS STORM AND HEAVY RAIN POTENTIAL TODAY AND
TONIGHT...THEN STORM CHANCES WEDNESDAY NIGHT AND FRIDAY WHICH
SANDWICH A POSSIBLE 90 PLUS DEGREE DAY ON THURSDAY. LESS BUT
STILL SOME TIME WAS SPENT ON THE FINAL CHALLENGE OF HOW MUCH OF A
COOL DOWN OCCURS THE FIRST FULL WEEKEND OF THIS NEW METEOROLOGICAL
SEASON.

SYNOPSIS...
A LONG WAVE TROUGH EXTENDING SOUTHWARD THROUGH CANADA INTO THE NORTH
CENTRAL U.S. HAS A VERY PROGRESSIVE SHORT WAVE FEATURE MOVING
THROUGH ITS SOUTHERN BASE. THIS IS SPEEDING EAST-NORTHEAST ACROSS
IA EARLY THIS MORNING. A SURFACE COLD FRONT MOVING EAST LAGS THIS
SHORT WAVE...EXTENDING FROM NORTHERN MN THROUGH THE TX PANHANDLE
EARLY THIS MORNING...WITH MULTIPLE SURFACE WAVES IN THE 1003MB
NEIGHBORHOOD ALONG IT. NORTHWEST SURFACE FLOW BEHIND THIS FRONT IS
NOT PARTICULARLY STRONG SO THIS FRONT WILL CONTINUE TO BE A SLOW-
MOVER TODAY...NOT EXPECTED TO ENTER THE FORECAST AREA UNTIL THIS
EVE. BEING WITHIN A WARM SECTOR UNDER QUICKENING UPPER/MID-LEVEL
FLOW PRESENTS THE STORM CHANCES THESE 24 HOURS.

THIS MORNING...
A LOOSELY DEFINED MCS MOVING EASTWARD INTO NORTHWEST IL EARLY THIS
MORNING WANED CONSIDERABLY WITH WARMING CLOUD TOPS AND OUTFLOW
EXTENDING WELL AHEAD OF IT. SEEING AN UPTICK ACROSS WEST CENTRAL IL
LIKELY ASSOCIATED WITH LIFT OF THE AFOREMENTIONED PROGRESSIVE SHORT
WAVE. HIGH RESOLUTION MODELS GREATLY VARY ON WHAT WILL HAPPEN EVEN
JUST A FEW HOURS OUT...BUT WOULD EXPECT SYNOPTICALLY TO SEE SOME
CONVECTION EVOLVE INTO THE FORECAST AREA THIS MORNING...POSSIBLY
ONLY THE WESTERN/SOUTHWESTERN AREA BUT STILL CANT RULE OUT SCATTERED
ACTIVITY MOVING EASTWARD THROUGH THE ENTIRE AREA INCLUDING
CHICAGO DURING MID/LATE MORNING. DESPITE A FAIRLY STRONG LOW-LEVEL
JET INTO ANY ACTIVITY...THE CONTINUED BROAD AREA OF STORMS ACROSS
EASTERN KS INTO WEST/SOUTHWEST MO THROUGH EARLY TO MID MORNING
SHOULD LESSEN MOISTURE TRANSPORT AND THUS ABILITY TO REALIZE STEEP
LAPSE RATES ALOFT FOR MORE ROBUST ACTIVITY...AND MAYBE EVEN
THUNDER IN GENERAL NORTH OF INTERSTATE 80.

THIS AFTERNOON AND TONIGHT...
DESPITE THIS BEING IN THE FIRST 12 HOURS OF THE FORECAST...DUE TO
INFLUENCE OF MORNING STORMS AND LARGE MODEL DIFFERENCES...CONFIDENCE
ON SPECIFICS IN THESE PERIODS REMAIN LOW. THERE SHOULD BE SOME
FORM OF OUTFLOW BOUNDARY OR BOUNDARIES FROM MORNING ACTIVITY/CLOUD
COVER THAT LINGER INTO THE FORECAST AREA INTO THE AFTERNOON...MOST
FAVORED SOUTH OF INTERSTATE 80. AS WARMING AND DESTABILIZATION
OCCURS WITH DEW POINTS AROUND 70F...COULD SEE SCATTERED ACTIVITY
DEVELOP NEAR ANY SUCH BOUNDARIES DURING THE MID TO LATE AFTERNOON.
THE SECOND UPPER WAVE ACROSS WESTERN WY THIS MORNING WILL BEGIN TO
APPROACH THE REGION AS WELL BY LATE IN THE DAY...WITH FORCING FROM
THIS POSSIBLY AIDING IN SCATTERED STORM DEVELOPMENT ACROSS MUCH OF
THE REGION. EVEN EARLY THIS MORNING THERE ARE A HANDFUL OF STORMS
ACROSS THE UPPER MIDWEST NOT LINKED TO ANY SPECIFIC SURFACE
FEATURE. INCREASING DEEP LAYER SHEAR OF 35 TO 50 KT WILL SUPPORT
ISOLATED TO SCATTERED SEVERE DISCRETE STORMS IN THE REGION.

WHILE IT REMAINS DIFFICULT TO PINPOINT TIMING...IT WOULD SEEM THE
GREATEST COVERAGE IN REDEVELOPING STORMS THIS EVENING WOULD BE IN
THE SOUTHERN FORECAST AREA WHERE AFOREMENTIONED BOUNDARY MAY OCCUR
AND MODEST SOUTHWEST 850-925MB FLOW AND MOISTURE TRANSPORT
REMAINS. AS THE AREA BECOMES UNDER A RIGHT ENTRANCE REGION TO THE
UPPER JET...DO EXPECT INCREASING ASCENT TONIGHT IN THE REGION FOR
MORE ROBUST CONVECTION AND POTENTIAL SEVERE AND HEAVY RAIN
THREATS. RIGHT NOW A GUIDANCE OVERLAP WOULD INDICATE THE FAR
SOUTHEAST FORECAST AREA IS MOST FAVORED FOR THIS. PRECIPITABLE
WATERS AROUND TWO INCHES AND STORM MOTIONS NEARLY PARALLEL TO THE
UPPER AND MID LEVEL FLOW WILL PRESENT HEAVY RAIN THREATS IN
THE GENERAL CENTRAL TO SOUTHERN IL INTO IN REGIONS...BUT AGAIN AT
THIS TIME CONFIDENCE VARIES ON PLACEMENT. BECAUSE OF THAT WILL
CONTINUE WITH THE HYDROLOGIC OUTLOOK /ESF/ FOR THE AREAS HIT HARD
ON SATURDAY NIGHT WITH HEAVY RAINFALL.

TUESDAY AND WEDNESDAY...
THE FRONT SHOULD CLEAR THE FORECAST AREA SOMETIME TUESDAY MORNING.
WHILE DRY AIR ADVECTION WILL OCCUR...LIMITED CONVERGENCE REMAINS
IN THE SOUTHEAST FORECAST AREA FOR POSSIBLY A STORM OR TWO TUESDAY
BUT IT LOOKS TO BE A LOW CHANCE. TEMPERATURES ONLY COOL SLIGHTLY
AS HIGH PRESSURE QUICKLY MOVES ATOP THE AREA TUESDAY NIGHT AND
THEN EASTWARD.

WEDNESDAY NIGHT THROUGH FRIDAY...
WARM AIR ADVECTION AND A RAPID PRECIPITABLE WATER INCREASE IS
FORECAST WEDNESDAY NIGHT ON ALL GUIDANCE. FEEL THAT MODELS MAY BE
UNDER-DOING THE STORM CHANCES GIVEN FORECAST PROFILES OF STEEPENING
LAPSE RATES WITHIN A RAPIDLY MOISTENING COLUMN...AT LEAST IN THE
WESTERN FORECAST AREA. SO HAVE INCREASED POPS IN THAT AREA. AS FOR
THURSDAY...HAVE GONE DRY IN MANY AREAS COLLABORATING AND
UNDERCUTTING A MODEL BLEND OF POPS. THE SYNOPTIC PATTERN FAVORS A
HOT DAY AND BARRING ANY STRATUS ISSUES WITH WEDNESDAY NIGHTS WARM
AIR ADVECTION AND POSSIBLE PRECIP...SHOULD SEE THE 90 DEGREE MARK
REACHED OR EXCEEDED ACROSS A GOOD PART OF THE FORECAST AREA BASED
ON STRONG SOUTHWEST FLOW AND FORECAST 850MB AND 925MB TEMPERATURES
COMPARED TO CLIMATOLOGY. FOR NOW HAVE KEPT THE NORTH A LITTLE
BELOW THAT WITH THE POSSIBILITY OF MORNING CLOUDS. THE SYSTEM
COLD FRONT IS PRESENTLY FORECAST BY THE EC AND THE GFS TO COME
THROUGH THE AREA SOMETIME ON FRIDAY WHICH WOULD BRING STORM
CHANCES WITH IT...AS WELL AS FLOW TURNING OFF THE LAKE BEHIND ITS
PASSAGE.

BEYOND...
NO CHANGES MADE TO THIS WEEKEND WHERE HIGHS LOOK TO BE AROUND 70
WITH DRY CONDITIONS BEHIND THE AFOREMENTIONED FRONT. HIGH PRESSURE
AROUND 1023MB IS FORECAST BY A BLEND OF GUIDANCE. GIVEN THE 925MB
TEMPERATURES FORECAST IF THAT HIGH IS CENTERED OVER THE FORECAST
AREA SOMETIME SUNDAY OR MONDAY NIGHTS /7TH OR 8TH/...LOWS IN
OUTLYING AREAS WOULD LIKELY BE IN THE 40S.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010733
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010733
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
232 AM CDT

IT LOOKS TO BE AN ACTIVE WEATHER DAY ACROSS THE LAKE...WITH STOUT
SOUTHERLY WINDS LAKE-WIDE...AND THE THREAT FOR SOME STRONG TO SEVERE
THUNDERSTORMS ACROSS SOUTHERN LAKE MICHIGAN. THESE STRONG SOUTHERLY
WINDS WILL RESULT IN WINDS AROUND 25 KT AND THE ONGOING SMALL CRAFT
ADVISORY STILL APPEARS GOOD. THE SURFACE LOW...RESPONSIBLE FOR THESE
STRONG SOUTHERLY WINDS TODAY...WILL SHIFT ACROSS ONTARIO...AND TO
NEAR JAMES BAY BY THIS EVENING WHILE DEEPENING TO AROUND 29.2
INCHES. AS THIS OCCURS...AN ASSOCIATED COLD FRONT WILL BE DRAWN
EASTWARD ACROSS THE LAKE BY EARLY TUESDAY MORNING. WINDS WILL BECOME
WESTERLY AND ABATE SIGNIFICANTLY WITH THE PASSAGE OF THIS FRONT.

ANOTHER PERIOD OF STRONGER SOUTHERLY WINDS LOOKS TO SET UP AGAIN
WEDNESDAY NIGHT AND THURSDAY AS ANOTHER POTENT AREA OF LOW PRESSURE
TRACKS EASTWARD ACROSS ONTARIO. WINDS SPEEDS COULD AGAIN BE AROUND
25 KT OUT OF THE SOUTH DURING THIS PERIOD. ANOTHER STRONGER COLD
FRONT LOOKS TO SHIFT DOWN THE LAKE IN THE WAKE OF THIS LOW LATE
FRIDAY AND THIS COULD SET THE STAGE FOR A DECENT NORTHERLY WIND
EVENT ACROSS THE LAKE AS A STOUT AREA OF HIGH PRESSURE QUICKLY
BUILDS EASTWARD ACROSS THE UPPER MIDWEST. STRONG NORTHERLY WINDS OF
25 TO 30 KT APPEAR QUITE POSSIBLE IN THE WAKE OF THIS COLD FRONT
FRIDAY NIGHT INTO SATURDAY...WHICH WOULD ALSO RESULT IN LARGE WAVES
IN EXCESS OF 5 FEET ACROSS SOUTHERN LAKE MICHIGAN INTO NEXT
WEEKEND.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 010616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
116 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 010616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
116 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

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000
FXUS63 KLOT 010616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
116 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 010616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
116 AM CDT MON SEP 1 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF SHRA/TSRA POSSIBLE THIS MORNING AFTER 13-14 UTC.
* ADDITIONAL SHOWERS/STORMS POSSIBLE EITHER LATER THIS AFTERNOON
  OR THIS EVENING.
* GUSTY SOUTHWEST WINDS DURING THE DAY.

KJB

//DISCUSSION...UPDATED 06Z...

CONVECTIVE CHANCES AND TIMING WILL BE THE PRIMARY WEATHER CONCERN
AND FOCUS FOR THE AREA TODAY.

AN AREA OF ONGOING CONVECTIVE ACTIVITY OVER EASTERN IOWA AND INTO
MISSOURI IS GRADUALLY SHIFTING TO THE EASTWARD. ALTHOUGH A WEAKENING
TREND IS EXPECTED OVERNIGHT WITH THIS ACTIVITY...IT APPEARS THAT THE
REMNANTS MAY HOLD TOGETHER TO PRODUCE AT LEAST SOME SHOWERY
ACTIVITY...WITH SOME EMBEDDED THUNDER THIS MORNING. CURRENT TIMING
BRINGS THIS ACTIVITY ACROSS KRFD AFTER 09 UTC...THROUGH AROUND 11
UTC...WITH THE ACTIVITY SHIFTING OVER THE EASTERN TERMINALS AFTER
13-14 UTC THIS MORNING. THE WINDS COULD TEMPORALLY BE MESSY DURING
THE MORNING AS THIS ACTIVE PUSHES OVER THE TERMINALS...BUT OVERALL A
SOUTHWESTERLY WIND COMPONENT SHOULD BE THE RULE DURING THE DAY. IT
ALSO APPEARS TO BE A BREEZY DAY...WITH SOUTHWESTERLY WIND GUSTS UP
TO 25 KT EXPECTED.

UNCERTAINTY IS HIGH IN WHETHER OR NOT ANY AFTERNOON AND EVENING
CONVECTION WILL FIRE OVER THE TERMINALS. THE MORNING ACTIVITY LOOKS
TO SUBDUE AFTERNOON DESTABILIZATION SOME...AND IT IS QUITE POSSIBLE
THAT THE MAIN AXIS OF AFTERNOON CONVECTIVE ACTIVITY OCCURS JUST SOUTH
OF THE TERMINALS. HOWEVER...IN SPITE OF THESE UNCERTAINTIES...I FELT
JUSTIFIED IN ADDING A PROB 30 GROUP FOR THUNDER DURING THE EVENING
TODAY. ANOTHER STOUT UPPER LEVEL DISTURBANCE IS EXPECTED TO MOVE OVER
NORTHERN ILLINOIS AS THE COLD FRONT APPROACHES THIS EVENING AND I
THINK THERE IS A DECENT POSSIBILITY THAT IF THE AFTERNOON ACTIVITY
FIRES SOUTH OF US THAT THERE COULD BE SOME ADDITIONAL ACTIVITY
FARTHER NORTH ASSOCIATED WITH THIS APPROACHING DISTURBANCE. TIMING
AT THIS JUNCTURE IS VERY DIFFICULT TO PIN DOWN...AND WILL NEED TO BE
IRONED OUT AS WE GET A BETTER HANDEL ON TRENDS THROUGH THE DAY.
EITHER WAY...THERE WILL LIKELY BE AREAS OF CONVECTIVE ACTIVITY THIS
AFTERNOON AND TONIGHT SOUTH OF THE TERMINALS.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES THROUGH THE DAY.
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 010452
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1152 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KILX 010452
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1152 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KILX 010452
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1152 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KILX 010452
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1152 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1151 PM CDT SUN AUG 31 2014

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KLOT 010314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

//PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010224
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
924 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

&&

.PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 010224
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
924 PM CDT SUN AUG 31 2014

.DISCUSSION...
919 PM CDT

THE HIGHEST IMPACT WEATHER FOR THE LABOR DAY WEEKEND APPEARS TO BE
CONVECTIVE EVOLUTION ON THE LABOR DAY HOLIDAY. STILL SOME
UNCERTAINTY THIS EVENING WITH REGARDS TO HOW THINGS WILL PLAY OUT
WITH ALOT HINGING ON THE ACTIVE THUNDERSTORM ACTIVITY EXTENDING
FROM NORTHWEST WISCONSIN THEN SOUTH AND WEST ACROSS
MINNESOTA...IOWA..AND INTO NORTHWEST KANSAS THIS EVENING.

AS MENTIONED IN THE PREVIOUS AFD...THERE IS SOME GUIDANCE THAT WANTS
TO DRIVE THIS ACTIVITY THROUGH OUR AREA IN THE MORNING...BUT
ENSEMBLES AND THE MAJORITY OF GUIDANCE IS SUGGESTING THAT THE
ACTIVITY LATE TONIGHT WILL WEAKEN OVER OUR AREA AS IT ENTERS A
LITTLE LESS HOSPITABLE THERMODYNAMIC ENVIRONMENT...THOUGH THERE STILL LOOKS
TO BE SOME SHOWERS/STORMS POSSIBLE THROUGH THE MORNING HOURS. SOME
OF THESE MAY BE SEVERE AS THERE IS STILL MODEST INSTABILTY AND SHEAR
WILL BE MORE THAN AMPLE AND THERE IS A PROGRESSIVE AND SOMEWHAT
NEGATIVELY TILTED FAST MOVING WAVE PASSING THROUGH THE AREA. IT IS
THIS TIME FRAME WHERE OUR NORTHERN AND WESTERN AREAS APPEAR TO HAVE
A SLIGHTLY HIGHER POTENTIAL FOR SEVERE STORMS. WE WILL LIKELY GET
SOME CONVECTIVE DEBRIS FROM STORMS TO THE WEST...THEN BEFORE
ATMOSPHERE RELOADS AHEAD OF THE APPROACHING COLD FRONT...IT LOOKS
LIKE THERE COULD BE A PERIOD OF DRIER CONDITIONS.

AND WHILE MODELS STILL SUGGEST THAT THERE IS A SEVERE WEATHER/HEAVY
RAINFALL THREAT AREA-WIDE ON MONDAY...THERE ARE SIGNS THAT AREAS
SOUTH AND EAST...AGAIN ROUGHLY SOUTH OF INTERSTATE 80 AND ALONG AND
EAST OF INTERSTATE 55 MAY BE THE HOT SPOT FOR SEVERE STORMS LATER IN
THE DAY AND POSSIBLY EVEN MORE NOTABLY SOME VERY HEAVY RAINFALL. THESE
AREAS RECEIVED A HEALTHY DOSE OF RAINFALL ON SATURDAY NIGHT AND 1 HR
FLASH FLOOD GUIDANCE IN THESE AREAS IS ANYWHERE FROM 1-1.5". WITH
PWATS AROUND 2" AHEAD OF THE FRONT...THIS CAN EASILY BE ACHEIVED IN
ANY STRONGER STORMS.  QUESTIONS STILL REMAIN AS TO HOW PROGRESSIVE
THE FRONT WILL BE WHICH PRECLUDES FLASH FLOOD WATCH ISSUANCE AT THIS
TIME...BUT WE HAVE DECIDED TO ISSUE AN ESF TO HIGHLIGHT THE ENHANCED
POTENTIAL IN THESE AREAS AND HIT THESE AREAS WITH THE HIGHEST POPS
MONDAY EVENING. REASONING BEING IS THAT THERE LOOKS TO BE A PERIOD
OF STORMS IN THE AFTERNOON AHEAD OF THE FRONT...BUT DURING THE
EVENING THE UPPER LEVEL JET IS STILL STRENGTHENING AND IS ORIENTED
PARALLEL TO THE SURFACE FRONT WHICH MAY PRECLUDE THE FRONT FROM
SHIFTING SOUTHEAST TOO QUICKLY. EVEN IF STORMS CONGEAL INTO A LINE
LATER IN THE EVENING...THEY WILL STILL BE EFFICIENT RAIN PRODUCERS.
STILL EXPECT STORMS TO CONTINUE TO FESTER FOR AREAS NORTH AND WEST
OF THIS TARGET AREA IN THE EVENING AS THE FRONT DOES NOT COMPLETELY
CLEAR THE AREA UNTIL POSSIBLY TUESDAY MORNING.

KMD

&&

.PREV DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 010207
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
907 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 646 PM CDT SUN AUG 31 2014

Storm complex getting going over the central Plains this evening.
While there is some model spread in how quickly this complex, or
its remnants, gets here, most models suggest it reaching KPIA
close to sunrise and heading east from there. This complex should
die out during the morning, but afternoon redevelopment is likely
along associated outflows. At this point, plan to keep forecast
mainly VFR, with a VCTS/VCSH mention around the best estimate of
arrival time for complex remnants and/or redevelopment.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KILX 010207
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
907 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 858 PM CDT SUN AUG 31 2014

Aside from a few spotty showers in east central Illinois, quiet
conditions prevail across the forecast area this evening, and
should for most if not all of the night. The main thing that may
disrupt the quiet weather before morning, and it looks rather
impressive at the moment, is the storm complex approaching from
the Plains & upper Midwest. This complex is being driven by a
seasonably strong upper level jet/wave, and 45-50 kt low level
jet. Expect this complex, although it should be on the downswing
in intensity, to begin to impact areas west of the Illinois River
after 4 AM.

Going forecast has overnight scenario well covered. Only minor
tweaks have been needed to the hourly trends.

&&

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 646 PM CDT SUN AUG 31 2014

Storm complex getting going over the central Plains this evening.
While there is some model spread in how quickly this complex, or
its remnants, gets here, most models suggest it reaching KPIA
close to sunrise and heading east from there. This complex should
die out during the morning, but afternoon redevelopment is likely
along associated outflows. At this point, plan to keep forecast
mainly VFR, with a VCTS/VCSH mention around the best estimate of
arrival time for complex remnants and/or redevelopment.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK







000
FXUS63 KILX 010013
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
713 PM CDT Sun Aug 31 2014

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 646 PM CDT SUN AUG 31 2014

Storm complex getting going over the central Plains this evening.
While there is some model spread in how quickly this complex, or
its remnants, gets here, most models suggest it reaching KPIA
close to sunrise and heading east from there. This complex should
die out during the morning, but afternoon redevelopment is likely
along associated outflows. At this point, plan to keep forecast
mainly VFR, with a VCTS/VCSH mention around the best estimate of
arrival time for complex remnants and/or redevelopment.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK






000
FXUS63 KILX 010013
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
713 PM CDT Sun Aug 31 2014

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 646 PM CDT SUN AUG 31 2014

Storm complex getting going over the central Plains this evening.
While there is some model spread in how quickly this complex, or
its remnants, gets here, most models suggest it reaching KPIA
close to sunrise and heading east from there. This complex should
die out during the morning, but afternoon redevelopment is likely
along associated outflows. At this point, plan to keep forecast
mainly VFR, with a VCTS/VCSH mention around the best estimate of
arrival time for complex remnants and/or redevelopment.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BAK







000
FXUS63 KLOT 312331
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
631 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 312331
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
631 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PERIOD OF SHRA/TSRA POSSIBLE MONDAY
* GUSTY SOUTHWEST WINDS POSSIBLE MONDAY

IZZI

//DISCUSSION...UPDATED 00Z...

INTENSE THUNDERSTORMS DEVELOPING OVER EASTERN NEBRASKA/WESTERN
IOWA WILL LIKELY CONGEAL INTO A LARGE CLUSTER AND MOVE EAST ACROSS
IOWA TONIGHT...ARRIVING IN NORTHWEST ILLINOIS TOWARD DAWN. MODELS
SUGGEST THESE STORMS WILL WEAKEN OR COMPLETELY DISSIPATE AS THEY
MOVE ACROSS NORTHERN ILLINOIS MONDAY MORNING...HOWEVER CONFIDENCE
IN THAT SCENARIO IS NOT TERRIBLY HIGH AS CONVECTION COULD GROW
MORE ORGANIZED TONIGHT AND MAINTAIN ITSELF INTO THE MORNING
MONDAY. STORMS WILL EITHER RE-INTENSIFY OR RE-DEVELOP ALONG
REMNANT OUTFLOW BOUNDARY SUNDAY AFTERNOON...MAINLY SOUTHEAST OF
THE TERMINALS WITH STRONG-SEVERE THUNDERSTORMS POSSIBLY EXTENDING
FROM SOUTHEAST KANSAS NORTHEAST INTO NORTHERN INDIANA BY LATE
MONDAY AFTERNOON. BEST CHANCE OF SHRA/TSRA AT RFD WILL BE WITH
WEAKENING STORM COMPLEX APPROACHING FROM WEST MONDAY MORNING.
IMMEDIATE CHICAGO METRO TERMINALS LOOK TO HAVE BEST CHANCE OF
SHRA/TSRA FROM MID MORNING INTO THE MID AFTERNOON...EITHER WITH
WEAKENING CLUSTER MOVING IN FROM THE WEST OR WITH RENEWED
DEVELOPMENT ALONG OUTFLOW EARLY MONDAY AFTERNOON. A VERY PLAUSIBLE
ALTERNATIVE SCENARIO IS THAT OVERNIGHT STORM COMPLEX COULD
LARGELY DISSIPATE BEFORE REACHING CHICAGO METRO AREA FOLLOWED BY
REDEVELOPMENT SOUTHEAST OF THE AREA LEAVING CHICAGO AREA TERMINALS
WITH LITTLE NO SHRA/TSRA ACTIVITY. CONFIDENCE IN CONVECTIVE
EVOLUTION IS LOW SO HANDLED WITH PROB30 FOR NOW ATTEMPTING TO
PINPOINT MOST LIKELY TIMING.

 ANY WELL ORGANIZED SHRA/TSRA COULD RESULT IN PERIODIC OF MORE
CHAOTIC WINDS MONDAY...OTHERWISE LOOK FOR LIGHT SOUTHERLY WINDS
TONIGHT WILL LIKELY BECOME SOUTHWESTERLY AND BECOME MODERATELY
STRONG/GUSTY MONDAY.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* FAIRLY LOW CONFIDENCE IN TSRA TIMING/CHANCES
* MEDIUM CONFIDENCE IN WINDS MONDAY
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

SATURDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 312206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
506 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD/IZZI

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 312206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
506 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD/IZZI

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 312206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
506 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD/IZZI

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 312206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
506 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD/IZZI

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311956
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
256 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311956
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
256 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 311943
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
243 PM CDT Sun Aug 31 2014

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1243 PM CDT SUN AUG 31 2014

MVFR ceilings will persist at the central Illinois terminals for
the next hour or two before gradually dissipating as the afternoon
progresses. Based on satellite trends, have scattered ceilings at
most sites by 19z, then at KDEC and KBMI by 20z. After that,
mostly clear skies will prevail through the evening before clouds
begin to increase from the west late tonight. A thunderstorm
complex currently developing across western Iowa/Nebraska will
track eastward tonight, with most model guidance keeping it west
of the Illinois River until 12z. Think storms will arrive in the
Illinois River Valley toward dawn in a weakening state, then
spread eastward across the area Monday morning. Have therefore
introduced low VFR ceilings and VCTS at KPIA after 12z, then
further east to KBMI and KDEC after 14/15z. Given plenty of
low-level moisture and relatively light winds, included slightly
reduced visbys down to 4sm at KCMI where skies will remain mostly
clear through dawn. Further west, think increasing clouds and wind
will prevent fog formation.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BARNES






000
FXUS63 KILX 311943
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
243 PM CDT Sun Aug 31 2014

.SHORT TERM...(This evening through Monday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

Vigorous short-wave evident on 18z/1pm water vapor imagery over
Colorado will be the primary weather-maker across central Illinois
over the next 24 hours.  As this feature pushes eastward, showers
and thunderstorms will become more numerous across western
Iowa/Nebraska this afternoon.  A complex of strong to severe
thunderstorms will eventually get organized, then begin pushing
eastward across Iowa overnight.  Most model guidance keeps this
convection west of Illinois until around 12z.  Have therefore
gone with a mostly dry forecast for tonight, with chance PoPs
arriving across the Illinois River Valley well after midnight.

Overnight thunderstorm complex will likely spill into west-central
Illinois Monday morning as it undergoes diurnal weakening.  While
gusty winds and brief heavy downpours may be possible with the
storms, the severe weather threat will remain low during the morning
hours.  Have gone with likely PoPs along/west of I-55 through
midday, with just chance PoPs further east and south.  Main question
on Monday will be when/where thunderstorms will re-develop during
the afternoon.  Colorado short-wave and accompanying cold front will
approach from the west late in the day, while outflow boundary from
morning convection will be around as well.  With plenty of
boundaries to develop on and strong upper support arriving, think
showers and thunderstorms will become likely across the northern
two-thirds of the CWA during the mid to late afternoon hours.
Forecast soundings indicate the atmosphere will have enough time to
destabilize after the morning clouds/showers, with CAPE values
reaching the 2000 to 3000J/kg range.  More impressive is the
projected 0-6 km bulk shear values, which climb into the 30 to 50kt
range.  If airmass can destabilize as expected, strong to severe
thunderstorms will be a good bet Monday afternoon/evening.  Any
storms that develop will be capable of producing large hail and
damaging wind gusts.  Have added severe/heavy rain mention to the
forecast accordingly.

&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 242 PM CDT SUN AUG 31 2014

A line of strong to severe storms is expected to in progress at the
start of Monday night, as a cold front pushes southeast across
Illinois. Forecast soundings indicate around 2000 J/kg MLCAPE and
0-6km shear of 40kt will continue into the evening. Those params
coupled with abundant moisture in the 1.7" to 2" PWATs will be
enough to fuel some rotating storms with hail and damaging winds.
Flash flooding will be a concern as well, especially as Monday
night progresses. The 300mb jet is expected to increase over the
western Great Lakes, putting central IL under the right entrance
divergent region. The line of storms is expected to become
oriented parallel to the steering flow later at night, allowing
for more training echoes, back-building, and very high rainfall
amounts. The higher threat for flooding will be mainly southeast
of I-72 Monday night, and heavy rain was added to the forecast
during that time frame.

Storm chances will continue into Tuesday for our southeast counties
due to the slower progress of the front, along with heavy rain
threat. Zonal flow will bring a few shortwave toward Illinois on
Wednesday, but any storms associated with them appear to lose
support as they depart farther from the thermal and theta-e ridges
in the Plains. We kept chance PoPs west of Springfield for Wed, with
slights east to I-57. Variable coverages of slight chance PoPs were
left in the extended through Thursday due to periodic waves of
energy that could trigger isolated showers/storms.

Storm chances increase in the north Thursday night as the next cold
front and upper trough approach IL. Widespread chance PoPs were left
in the forecast for Friday into Saturday as the cold front slowly
progresses southeast across the area.

Humidity will remain high from Tuesday through Friday, as afternoon
dewpoints climb from the upper 60s Tuesday to the low to mid 70s on
Thursday and Friday. High temps will be in the low to mid 80s on
Tue-Wed, but will warm into the upper 80s and low 90s Thur and
Friday ahead of the cold front Friday night. Much cooler temps and
dewpoints are forecast for Saturday and Sunday next weekend, with
highs on Sunday in the 70s and lows in the mid to upper 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1243 PM CDT SUN AUG 31 2014

MVFR ceilings will persist at the central Illinois terminals for
the next hour or two before gradually dissipating as the afternoon
progresses. Based on satellite trends, have scattered ceilings at
most sites by 19z, then at KDEC and KBMI by 20z. After that,
mostly clear skies will prevail through the evening before clouds
begin to increase from the west late tonight. A thunderstorm
complex currently developing across western Iowa/Nebraska will
track eastward tonight, with most model guidance keeping it west
of the Illinois River until 12z. Think storms will arrive in the
Illinois River Valley toward dawn in a weakening state, then
spread eastward across the area Monday morning. Have therefore
introduced low VFR ceilings and VCTS at KPIA after 12z, then
further east to KBMI and KDEC after 14/15z. Given plenty of
low-level moisture and relatively light winds, included slightly
reduced visbys down to 4sm at KCMI where skies will remain mostly
clear through dawn. Further west, think increasing clouds and wind
will prevent fog formation.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...SHIMON
AVIATION...BARNES







000
FXUS63 KLOT 311937
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
237 PM CDT SUN AUG 31 2014

.DISCUSSION...
226 PM CDT

SYNOPSIS...SEVERE WEATHER IS POSSIBLE TOMORROW WITH LARGE
HAIL...DAMAGING WINDS...AND FLASH FLOODING AS THE MAIN CONCERNS.
THE PATTERN REMAINS UNSETTLED WITH ADDITIONAL CHANCES OF
THUNDERSTORMS WEDNESDAY NIGHT THROUGH SATURDAY. TEMPS WILL BE ABOVE
NORMAL THROUGH FRIDAY WITH UPPER 80S POSSIBLE THURSDAY AND FRIDAY.
WE RETURN TO MORE SEASONAL TEMPS IN THE 70S NEXT WEEKEND.

THROUGH TONIGHT...
SLIGHT RIDGING ALOFT IS QUICKLY SHIFTING EAST AS A TROUGH DEEPENS
OVER THE PLAINS.  SURFACE HIGH PRESSURE IS ALSO SHIFTING EAST AS A
LOW DEEPENS OVER THE NORTH DAKOTA/MINNESOTA BORDER. CLOUD COVER IS
QUICKLY DIMINISHING THIS AFTERNOON AND TEMPS ARE RISING INTO THE MID
80S. COULD SEE A FEW ISOLATED SHOWERS THIS AFTERNOON OVER NW
INDIANA BUT NOT EXPECTING MUCH OUT OF THEM.

TONIGHT WILL START OUT CLEAR BUT CLOUDS WILL INCREASE AS THE LOW
APPROACHES. SOUTH WINDS WILL INCREASE OVERNIGHT SO NOT EXPECTING
FOG. LOWS WILL BE IN THE UPPER 60S TO LOW 70S.

MONDAY AND MONDAY NIGHT...
THE UPPER LEVEL TROUGH TOMORROW MORNING/AFTERNOON WHILE THE SURFACE
LOW STRETCHES FROM CENTRAL ONTARIO THROUGH WISCONSIN.  THE LOW WILL
CONTINUE TO DEEPEN AS IT MOVES OVER HUDSON BAY MONDAY EVENING.

THE CONVECTIVE SITUATION IS A TRICKY ONE AS TWO SCENARIOS ARE
POSSIBLE. IT ALL STARTS WITH THE CONVECTION FORMING OVER THE PLAINS.
THAT WILL FORM A COMPLEX AND REACH THE CWA EARLY TOMORROW MORNING.
THINKING AREAS WEST OF A HARVARD TO PONTIAC LINE WILL SEE SOME LEFT
OVER CONVECTION MONDAY MORNING...WITH A MUCH LESSER CHANCE OF STORMS
EAST OF THAT LINE.  IF THE STORMS STAY TOGETHER AND PASS OVER THE
ENTIRE CWA...WHICH SOME GUIDANCE MEMBERS SUGGEST...THIS COULD WORK
US OVER FOR THE DAY LIMITING CONVECTION LATER IN THE DAY.

HOWEVER...IF THE STORMS DISSIPATE EARLY IN THE MORNING AS I AM
EXPECTING...AFTERNOON CONVECTION WILL FORM AHEAD OF THE COLD FRONT.
GUIDANCE FEATURES CAPE VALUES OF 2000-3000 J/KG AND 0-6 KM SHEAR
VALUES WELL OVER 40 KT.  SUPERCELLS ARE POSSIBLE...BUT WITH STRONG
LINEAR FORCING FROM THE COLD FRONT...THINKING A LINE OF STORMS WILL
BE THE MAIN CONVECTIVE MODE.  THIS LINE WILL FORM AND IMPACT AREAS
SOUTHEAST OF A HIGHLAND PARK TO MENDOTA LINE.  AS MENTIONED
BEFORE...LARGE HAIL AND DAMAGING WINDS ARE THE MAIN SEVERE THREATS.

PWAT VALUES WILL BE AROUND 2 INCHES SO HEAVY RAIN IS ALSO VERY
LIKELY.  FLOW WILL BE STRONG TOMORROW SO EXPECTING THE STORMS TO
MOVE ALONG AT A GOOD PACE...BUT IF STORMS TRAIN...FLASH FLOODING IS
PROBABLE.

AREAS NORTHWEST OF THE HIGHLAND PARK TO MENDOTA LINE SHOULD BE
RELATIVELY QUIET AFTER THE MORNING CONVECTION DISSIPATES.  SOME
GUIDANCE MEMBERS KEEP THIS AREA DRY ALL DAY WHILE OTHERS FEATURE WEAK
FESTERING CONVECTION. NOT EXPECTING WIDESPREAD SEVERE WEATHER FOR
THIS REGION...BUT KEPT A SLIGHT CHANCE TO CHANCE OF THUNDERSTORMS IN
FOR NOW.  CONFIDENCE IS HIGH THAT SEVERE WEATHER WILL BE LIMITED IN
THIS REGION AND LOW ABOUT STORMS IN THE LATE AFTERNOON AND EVENING.

BREEZY CONDITIONS ARE EXPECTED OUTSIDE OF CONVECTIVE WIND GUSTS.
GUSTS ARND 25 MPH ARE EXPECTED IN THE AFTERNOON. DAYTIME HIGHS WILL
GET INTO THE LOW TO MID 80S.

THE COLD FRONT SHIFTS EAST OF THE REGION LATE MONDAY NIGHT INTO
EARLY TUESDAY MORNING WITH WINDS BECOMING NORTHWEST.  OVERNIGHT LOWS
WILL RANGE FROM THE LOW 60S IN NORTH CENTRAL IL TO THE UPPER 60S IN
NW INDIANA.

JEE

LONG TERM...TUESDAY THROUGH NEXT SUNDAY...

MONDAY/MONDAY NIGHTS UPPER TROUGH AND SURFACE COLD FRONT WILL BE
EXITING THE AREA EARLY TUESDAY MORNING...WITH RISING HEIGHTS
DEVELOPING IN THE WAKE OF THE DEPARTING TROUGH WHILE UPPER FLOW
BECOMES FAIRLY ZONAL ACROSS THE CONUS. HAVE HELD ONTO SOME CHANCE
POPS ALONG THE FRONT IN OUR SOUTHEASTERN CWA WHERE RAIN MAY BE
ONGOING 12-15Z TUESDAY...WITH AREA THEN DRYING OUT DURING THE DAY AS
WEAK SURFACE HIGH PRESSURE SPREADS ACROSS THE AREA BY TUESDAY
EVENING. QUIET WEATHER CONTINUES TUESDAY NIGHT AS THE HIGH DRIFTS
EAST ACROSS THE AREA TO THE LOWER LAKES AND UPPER OHIO VALLEY BY
WEDNESDAY MORNING. WHILE DEW POINT TEMPS WILL DROP OFF BEHIND THE
FRONT...AIR TEMPS TUESDAY SHOULD BE CLOSE TO THOSE MONDAY...WITH
HIGHS IN THE LOWER 80S IN MOST SPOTS. LIGHT WINDS AND LOWER DEW
POINTS SHOULD ALLOW TEMPS IN THE LOW-MID 60S FOR OVERNIGHT LOWS...
AND PERHAPS EVEN AN UPPER 50 OR TWO IN SOME OF OUR TYPICAL COOL
SPOTS.

ATTENTION THEN TURNS TO THE WEST AS ANOTHER UPPER TROUGH PROPAGATES
EASTWARD ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS REGION...
WITH A SURFACE LOW PRESSURE TROUGH DEVELOPING FROM THE CENTRAL
PLAINS NORTHEAST INTO NORTHWEST MINNESOTA BY EVENING. THIS RESULTS
IN RETURN SOUTHERLY LOW LEVEL FLOW DEVELOPING ACROSS THE PLAINS AND
MISSISSIPPI VALLEY REGION WITH WARM/MOIST LOW LEVEL AIR RETURNING
ESPECIALLY WEST OF THE FORECAST AREA DURING THE DAY AND SPREADING
INTO THE CWA WEDNESDAY NIGHT AS LOW PRESSURE CENTER DEVELOPS ACROSS
THE UPPER MIDWEST AHEAD OF THE AFOREMENTIONED UPPER TROUGH. WARMING
TEMPS IN THE 950-850 HPA LAYER EXPECTED TO PROVIDE WARMER SURFACE
TEMPS INTO THE MID-80S IN MOST AREAS...WITH HUMIDITY RETURNING AS
DEW POINT TEMPS CLIMB BACK INTO THE MID-UPPER 60S. SOME INCREASE IN
CLOUD COVER IS LIKELY ESPECIALLY LATER IN THE DAY...ASSOCIATED WITH
WARM FRONT OVER THE MISSISSIPPI VALLEY AND ISENTROPIC ASCENT AND
MOIST ADVECTION IN THE DEVELOPING SOUTH-SOUTHWEST WIND REGIME.
VARIOUS GUIDANCE SOLUTIONS SUGGEST SOME POTENTIAL FOR SCATTERED
SHOWERS/THUNDERSTORMS TO AFFECT PARTS OF THE CWA BY WEDNESDAY NIGHT
AS WARM FRONT DEVELOPS NORTHEAST ACROSS THE AREA...THOUGH GREATER
CHANCE APPEARS TO BE FROM WEST OF THE MISSISSIPPI RIVER NORTH INTO
WISCONSIN ON NOSE OF STRONGER LOW LEVEL JET WINDS AND STRONGER
WESTERLIES.

SCATTERED THUNDERSTORM POTENTIAL LINGERS IN THE WARM/MOIST AND
POTENTIALLY UNSTABLE WARM SECTOR THURSDAY...THOUGH THE BEST CHANCES
OF PRECIP APPEAR TO BE LATE THURSDAY NIGHT THROUGH FRIDAY AS LOW
PRESSURE PASSES NORTH OF THE LAKES AND COLD FRONT TRAILS ACROSS THE
FORECAST AREA. STRONGER DEEP LAYER SHEAR LAGS THE FRONT TO THE NORTH
AND LIMITS WIDESPREAD SEVERE POTENTIAL IT APPEARS...THOUGH
SOUTHWEST-NORTHEAST ORIENTATION OF THE BOUNDARY ALIGNED WITH
MID-LEVEL WIND FIELD SUGGESTS SOME LOCALLY HEAVY RAINFALL MAY AGAIN
BE POSSIBLE WITH FORECAST PWATS ABOVE 1.50". VERY WARM AND HUMID
CONDITIONS EXPECTED DURING THE THURSDAY-FRIDAY PERIOD WITH TEMPS
RISING INTO THE UPPER 80S/AROUND 90 DEPENDENT UPON CLOUD COVER AND
THUNDERSTORM TRENDS. FRONT DRIFTS SOUTHEAST FRIDAY/FRIDAY EVENING
MAINTAINING THUNDERSTORM THREAT...BEFORE CLEARING FORECAST AREA
SATURDAY AS HIGH PRESSURE BUILDS ACROSS THE UPPER MIDWEST/NORTHERN
LAKES. COOLER/DRIER WEATHER THEN ON THE HORIZON BY THE END OF NEXT
WEEKEND AS THE HIGH BUILDS ACROSS THE REGION WITH HIGH TEMPS IN THE
LOW-MID 70S SUNDAY AND LOWS IN THE 50S.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 311850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
149 PM CDT

THE WEATHER PATTERN ACROSS THE WESTERN LAKES WILL BE FAIRLY
PROGRESSIVE OVER THE NEXT SEVERAL DAYS...WITH A PAIR OF SURFACE LOWS
PASSING ACROSS OR NORTH OF THE NORTHERN LAKES AND TRAILING COLD
FRONTS ACROSS LAKE MICHIGAN.

THE FIRST LOW...OVER FAR NORTHWEST MINNESOTA THIS AFTERNOON...WILL
MOVE NORTHEAST ACROSS ONTARIO AND THE NORTHERN LAKES THROUGH MONDAY
WITH ITS TRAILING COLD FRONT PUSHING SOUTHEAST ACROSS THE LAKE
MONDAY AFTERNOON AND EVENING. TIGHTENING OF THE GRADIENT AHEAD OF
THE LOW AND FRONTAL TROUGH WILL RESULT IN SOUTHERLY WINDS INCREASING
LATE TONIGHT AND MONDAY...WITH GUSTS REACHING THE 20-25 KT RANGE AND
CONTINUING INTO EARLY MONDAY EVENING BEFORE THE GRADIENT WEAKENS
ALONG THE COLD FRONTAL TROUGH. THIS FRONT WILL PUSH SOUTHEAST ACROSS
THE LAKE MONDAY NIGHT...WITH LIGHTER WINDS OVERNIGHT AND TUESDAY AS
A BUBBLE HIGH MOVES ACROSS THE AREA BEHIND THE FRONT.

THE HIGH WILL MOVE OFF TO THE EAST WEDNESDAY MORNING...WITH WINDS
BECOMING SOUTH AND STRENGTHENING TO 20-25 KT AGAIN LATER IN THE
WEDNESDAY AND CONTINUING INTO THURSDAY BEFORE THE NEXT SURFACE LOW
PASSES NORTH OF THE LAKES AND ITS TRAILING COLD FRONT MOVES THROUGH
LATE THURSDAY NIGHT AND EARLY FRIDAY. WINDS DONT LOOK TO BE TOO
STRONG IMMEDIATELY BEHIND THIS SECOND FRONT...THOUGH A PERIOD OF
ENHANCED NORTHERLY WINDS IS POSSIBLE SATURDAY AS HIGH PRESSURE
BUILDS IN BEHIND THE FRONT.

WITH GUSTY SOUTH WINDS MONDAY...A SMALL CRAFT ADVISORY HAS BEEN
ISSUED FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS FROM
MID-MORNING THROUGH MORNING EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 10 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 311743
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1243 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 948 AM CDT SUN AUG 31 2014

A low overcast persists across much of central Illinois along and
east of a Peoria to Jacksonville line this morning. 1430z visible
satellite imagery is showing thin spots developing in the cloud
cover, so am expecting it to dissipate within the next 2 to 3
hours. HRRR ceiling forecast shows this trend quite nicely,
resulting in a partly to mostly sunny afternoon. May see a few
showers/thunder pop up along/south of I-70: however, areal
coverage will remain spotty. Updated the forecast to better
reflect sky cover trends this morning and to confine PoPs to just
the far SE KILX CWA.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1243 PM CDT SUN AUG 31 2014

MVFR ceilings will persist at the central Illinois terminals for
the next hour or two before gradually dissipating as the afternoon
progresses. Based on satellite trends, have scattered ceilings at
most sites by 19z, then at KDEC and KBMI by 20z. After that,
mostly clear skies will prevail through the evening before clouds
begin to increase from the west late tonight. A thunderstorm
complex currently developing across western Iowa/Nebraska will
track eastward tonight, with most model guidance keeping it west
of the Illinois River until 12z. Think storms will arrive in the
Illinois River Valley toward dawn in a weakening state, then
spread eastward across the area Monday morning. Have therefore
introduced low VFR ceilings and VCTS at KPIA after 12z, then
further east to KBMI and KDEC after 14/15z. Given plenty of
low-level moisture and relatively light winds, included slightly
reduced visbys down to 4sm at KCMI where skies will remain mostly
clear through dawn. Further west, think increasing clouds and wind
will prevent fog formation.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...BARNES







000
FXUS63 KILX 311743
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1243 PM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 948 AM CDT SUN AUG 31 2014

A low overcast persists across much of central Illinois along and
east of a Peoria to Jacksonville line this morning. 1430z visible
satellite imagery is showing thin spots developing in the cloud
cover, so am expecting it to dissipate within the next 2 to 3
hours. HRRR ceiling forecast shows this trend quite nicely,
resulting in a partly to mostly sunny afternoon. May see a few
showers/thunder pop up along/south of I-70: however, areal
coverage will remain spotty. Updated the forecast to better
reflect sky cover trends this morning and to confine PoPs to just
the far SE KILX CWA.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1243 PM CDT SUN AUG 31 2014

MVFR ceilings will persist at the central Illinois terminals for
the next hour or two before gradually dissipating as the afternoon
progresses. Based on satellite trends, have scattered ceilings at
most sites by 19z, then at KDEC and KBMI by 20z. After that,
mostly clear skies will prevail through the evening before clouds
begin to increase from the west late tonight. A thunderstorm
complex currently developing across western Iowa/Nebraska will
track eastward tonight, with most model guidance keeping it west
of the Illinois River until 12z. Think storms will arrive in the
Illinois River Valley toward dawn in a weakening state, then
spread eastward across the area Monday morning. Have therefore
introduced low VFR ceilings and VCTS at KPIA after 12z, then
further east to KBMI and KDEC after 14/15z. Given plenty of
low-level moisture and relatively light winds, included slightly
reduced visbys down to 4sm at KCMI where skies will remain mostly
clear through dawn. Further west, think increasing clouds and wind
will prevent fog formation.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...BARNES






000
FXUS63 KLOT 311726
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1226 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311726
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1226 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311726
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1226 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311726
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1226 PM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE THIS AFTERNOON AND WHETHER OR NOT IT WILL PUSH
  ACROSS ORD/MDW.
* GUSTY SOUTHWEST WINDS DEVELOPING MID MORNING MONDAY.
* CHANCES FOR THUNDERSTORMS...WITH A LOWER CHANCE OF LINGERING
  PRECIP COMING IN TOMORROW MORNING...AND A BETTER CHANCE FOR NEW
  DEVELOPMENT OF STRONG THUNDERSTORMS MONDAY AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

THIS AFTERNOON...WEAK HIGH PRESSURE IS IN PLACE TODAY ALLOWING FOR
GENERALLY LIGHT SOUTHWEST FLOW. A LAKE BREEZE HAS ALREADY
DEVELOPED THOUGH REMAINS FAIRLY CLOSE TO THE SHORE AT THIS HOUR.
IT IS UNCERTAIN WHETHER IT WILL MAKE IT ACROSS THE TERMINALS BUT
MOST GUIDANCE IS LEANING AGAINST THIS OCCURRING...AND IF IT DOES IT
WOULD LIKELY BE LATE.

ATTENTION TURNS TO THE WEST TONIGHT AS AN UPPER LEVEL DISTURBANCE
PUSHES ACROSS THE PLAINS KICKING OFF THUNDERSTORMS. THESE
THUNDERSTORMS ARE EXPECTED TO PERSIST THROUGH THE OVERNIGHT HOURS
MOVING INTO NORTHERN ILLINOIS EARLY MONDAY MORNING IN A DISSIPATING
STAGE. RFD HAS BEST CHANCE FOR SEEING SOME FESTERING EARLY MORNING
ACTIVITY SO ADDED A PROB30 FOR TSRA. DEPENDING ON HOW FAR EAST THIS
PRECIP MAKES IT EARLY MONDAY...EXPECT THE ATMOSPHERE TO RECOVER
BECOMING MODERATELY UNSTABLE WITH ADDITIONAL THUNDERSTORMS EXPECTED
TO REDEVELOP MONDAY AFTERNOON. THESE STORMS COULD BE STRONG TO
SEVERE WITH GUSTY WINDS THE PRIMARY THREAT.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN LAKE BREEZE MAKING IT THROUGH ORD/MDW TODAY.
* LOW-MEDIUM CONFIDENCE IN CIGS REST OF TODAY.
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS AND DIRECTION MONDAY.
* HIGH CONFIDENCE IN AT LEAST A PERIOD OF TSRA BUT LOW CONFIDENCE
  IN SPECIFIC TIMING.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311608
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1108 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311608
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1108 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 311448
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
948 AM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 948 AM CDT SUN AUG 31 2014

A low overcast persists across much of central Illinois along and
east of a Peoria to Jacksonville line this morning. 1430z visible
satellite imagery is showing thin spots developing in the cloud
cover, so am expecting it to dissipate within the next 2 to 3
hours. HRRR ceiling forecast shows this trend quite nicely,
resulting in a partly to mostly sunny afternoon. May see a few
showers/thunder pop up along/south of I-70: however, areal
coverage will remain spotty. Updated the forecast to better
reflect sky cover trends this morning and to confine PoPs to just
the far SE KILX CWA.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 656 AM CDT SUN AUG 31 2014

Mainly IFR/MVFR visibilities this morning due to low ceilings and
areas of fog. Expect improving conditions through 14Z with
conditions generally becoming VFR as surface heating lifts
ceilings and dissipates fog. Isold TSRA to continue until around
00Z mainly K1H2-KPRG southward with potential MVFR cig/vsby and
gusty winds. After 00Z...TSRA ending with VFR conditions across
central/SE Illinois. Toward 12Z Monday...potential TSRA
development KIJX-KPIA westward depending on speed of approaching
system, but probability of TSRA and associated flight category
reductions too low probability before 12Z for mention in TAFS at
this time.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON






000
FXUS63 KILX 311448
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
948 AM CDT Sun Aug 31 2014

.UPDATE...
ISSUED AT 948 AM CDT SUN AUG 31 2014

A low overcast persists across much of central Illinois along and
east of a Peoria to Jacksonville line this morning. 1430z visible
satellite imagery is showing thin spots developing in the cloud
cover, so am expecting it to dissipate within the next 2 to 3
hours. HRRR ceiling forecast shows this trend quite nicely,
resulting in a partly to mostly sunny afternoon. May see a few
showers/thunder pop up along/south of I-70: however, areal
coverage will remain spotty. Updated the forecast to better
reflect sky cover trends this morning and to confine PoPs to just
the far SE KILX CWA.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 656 AM CDT SUN AUG 31 2014

Mainly IFR/MVFR visibilities this morning due to low ceilings and
areas of fog. Expect improving conditions through 14Z with
conditions generally becoming VFR as surface heating lifts
ceilings and dissipates fog. Isold TSRA to continue until around
00Z mainly K1H2-KPRG southward with potential MVFR cig/vsby and
gusty winds. After 00Z...TSRA ending with VFR conditions across
central/SE Illinois. Toward 12Z Monday...potential TSRA
development KIJX-KPIA westward depending on speed of approaching
system, but probability of TSRA and associated flight category
reductions too low probability before 12Z for mention in TAFS at
this time.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON







000
FXUS63 KLOT 311401
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
901 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311401
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
901 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311401
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
901 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311401
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
901 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN/BMD

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 311156
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
656 AM CDT Sun Aug 31 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 656 AM CDT SUN AUG 31 2014

Mainly IFR/MVFR visibilities this morning due to low ceilings and
areas of fog. Expect improving conditions through 14Z with
conditions generally becoming VFR as surface heating lifts
ceilings and dissipates fog. Isold TSRA to continue until around
00Z mainly K1H2-KPRG southward with potential MVFR cig/vsby and
gusty winds. After 00Z...TSRA ending with VFR conditions across
central/SE Illinois. Toward 12Z Monday...potential TSRA
development KIJX-KPIA westward depending on speed of approaching
system, but probability of TSRA and associated flight category
reductions too low probability before 12Z for mention in TAFS at
this time.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON






000
FXUS63 KILX 311156
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
656 AM CDT Sun Aug 31 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 656 AM CDT SUN AUG 31 2014

Mainly IFR/MVFR visibilities this morning due to low ceilings and
areas of fog. Expect improving conditions through 14Z with
conditions generally becoming VFR as surface heating lifts
ceilings and dissipates fog. Isold TSRA to continue until around
00Z mainly K1H2-KPRG southward with potential MVFR cig/vsby and
gusty winds. After 00Z...TSRA ending with VFR conditions across
central/SE Illinois. Toward 12Z Monday...potential TSRA
development KIJX-KPIA westward depending on speed of approaching
system, but probability of TSRA and associated flight category
reductions too low probability before 12Z for mention in TAFS at
this time.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON







000
FXUS63 KLOT 311132
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
632 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY THIS MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 12Z...

AS THE CLOUD SHIELD CLEARS OUT AND WITH CALM WINDS AND RESIDUAL
LOW LEVEL MOISTURE IN PLACE...SOME PATCHY FOG/STRATUS HAS
DEVELOPED. HOWEVER...WITH AMPLE SUNSHINE...EXPECT THAT THE
FOG/STRATUS WILL QUICKLY DISSIPATE BY MID MORNING WITH VFR
CONDITIONS EXPECTED THE REMAINDER OF THE DAY. WINDS SHOULD REMAIN
LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO DEVELOP...BUT THERE APPEARS
TO BE LITTLE PUSH BEHIND THE BOUNDARY...SO AT THIS POINT...FEEL
THAT CHANCES ARE LOW THAT THE LAKE BREEZE WILL PUSH INLAND OF
ORD/MDW. HOWEVER...IF THE LAKE BREEZE DOES MANAGE TO PUSH WEST OF
ORD/MDW...IT WOULD NOT BE UNTIL ARND 22-23Z AND ELY WINDS WOULD BE
ARND 5-7KT. ANOTHER APPROACHING COLD FRONT WILL BRING INCREASING
CHANCES FOR MORE SHOWERS AND THUNDERSTORMS BUT THIS WILL LIKELY
NOT BE UNTIL AFTER 12Z TOMORROW.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* LOW CONFIDENCE IN TIMING TS TOMORROW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE SHRA/TSRA.

TUESDAY AND WEDNESDAY...VFR. WX NIL.

THURSDAY THROUGH SATURDAY...PERIODIC CHANCES FOR SHRA/TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 310858
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
358 AM CDT Sun Aug 31 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1150 PM CDT SAT AUG 30 2014

Tricky aviation forecast for the first several hours of the 06Z
TAF valid time. Despite the loss of diurnal heating, convection
continues to fire along an outflow boundary from previous storms.
At this point, no terminal is immediately threatened by these
storms, though the band, and some associated outflow, is making a
gradual shift to the east. this would threaten at least KBMI
within the next few hours if they persist. Also, further east,
within a deeper moist layer, MVFR cigs have started to break out,
including at KDEC & KCMI. Have a hard time seeing how this will
improve before daybreak as slightly drier air filters in from the
west. Expect condtions to improve to or remain VFR areawide on
Saturday as the more active weather shifts off to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK







000
FXUS63 KILX 310858
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
358 AM CDT Sun Aug 31 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 358 AM CDT SUN AUG 31 2014

Shortwave trough and jet entrance region that brought banded
convection and some locally heavy precipitation to central IL last
evening has shifted northeastward with shower activity nearly ended
over the ILX CWA. With clearing skies and good radiational cooling,
patchy fog will continue to form overnight, mainly I-55
westward.

Moist conditions with enough instability will remain through the
afternoon today for a few showers and thunderstorms, mainly I-70
southeastward, but a relatively dry day expected. Highs in the mid
80s are expected.

After sunset, convection should end quickly across the CWA with the
loss of surface heating. Late in the night, chances for
thunderstorms will spread back into west central Illinois as another
cold front approaches from the west.

&&

.LONG TERM...(Monday through Saturday)
ISSUED AT 358 AM CDT SUN AUG 31 2014

SPC continues a slight risk (15+%) of severe thunderstorms across
central IL nw of a Flora to Robinson line Monday afternoon/evening
for damaging winds and large hail. This seems reasonable considering
surface to 6 km bulk shear values of 30-40 kts, CAPES of 2-3k J/kg.
Heavy rains also possible with thunderstorms in tropical airmass
ahead of frontal boundary. Short waves and 30-40 kt low level jet
moving into IL river valley later Sunday night into Monday morning
and then spreading into eastern IL Monday afternoon/evening. Upper
level trof over northern Rockies moves east into Midwest
Monday/Monday night and drives a cold front southeast across central
IL Monday night. Continued likely pops across much of area Monday
afternoon into Monday night, though diminishing pops overnight
Monday night nw of IL river. Best chances of showers and
thunderstorms lingers over areas from I-72 south on Tue especially
in the morning. The 5% risk of severe storms Tue is southeast of
Lawrenceville. Quite warm and humid Monday ahead of front with highs
82-88F and dewpoints 70-75F and warmest temps in southeast IL where
rain arrives later.

Frontal boundary to weaken as it moves se into Ohio River valley
Tue/Wed with near zonal upper level flow over the region. Carried
just slight chance of convection during midweek from Tue night
through Thu night. Highs in the low to mid 80s Tue/Wed climb into
mid 80s to around 90F Thu/Fri as dewpoints rise back into the low to
mid 70s with heat indices approaching 100F southern counties Thu/Fri
afternoon. Next frontal boundary press southeast into IL Friday
afternoon into Sat and bringing next best chances of showers and
thunderstorms and cooler temps during next weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1150 PM CDT SAT AUG 30 2014

Tricky aviation forecast for the first several hours of the 06Z
TAF valid time. Despite the loss of diurnal heating, convection
continues to fire along an outflow boundary from previous storms.
At this point, no terminal is immediately threatened by these
storms, though the band, and some associated outflow, is making a
gradual shift to the east. this would threaten at least KBMI
within the next few hours if they persist. Also, further east,
within a deeper moist layer, MVFR cigs have started to break out,
including at KDEC & KCMI. Have a hard time seeing how this will
improve before daybreak as slightly drier air filters in from the
west. Expect condtions to improve to or remain VFR areawide on
Saturday as the more active weather shifts off to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...ONTON
LONG TERM...07
AVIATION...BAK






000
FXUS63 KLOT 310834
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310834
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 AM CDT SUN AUG 31 2014

.DISCUSSION...
328 AM CDT

AFTER A FAIRLY QUIET DAY ACROSS THE AREA TODAY...ATTENTION QUICKLY
SHIFTS TO THE WEATHER FOR LABOR DAY INTO MONDAY NIGHT...DURING WHICH
PERIODS OF EXTREMELY HEAVY RAINFALL AND SEVERE WEATHER ARE POSSIBLE.

THUNDERSTORMS CONTINUED TO TRAIN ACROSS THE SAME AREAS ACROSS
PORTIONS OF FORD AND IROQUOIS COUNTIES IN ILLINOIS AND ALSO BENTON
COUNTY IN INDIANA YESTERDAY EVENING AND INTO THE OVERNIGHT HOURS.
THESE AREAS LIED IN THE RIGHT ENTRANCE REGION OF AN UPPER LEVEL JET
STREAK. THE COMBINATION OF THIS...AND THE CONTINUED LOW LEVEL
CONFLUENCE CONTINUED TO DRIVE THIS CONVECTION. RADAR ESTIMATES SOME
VERY HEFTY ISOLATED RAINFALL AMOUNTS IN EXCESS OF 4 INCHES ACROSS
PORTIONS OF THESE COUNTIES. ALTHOUGH SOME ISOLATED ACTIVITY
CONTINUES ACROSS THIS AREA AS OF THIS WRITING...IT IS EXPECTED THAT
ALL THIS ACTIVITY WILL SHIFT OUT OF THE AREA AROUND...OR JUST PRIOR
TO DAYBREAK AS THE UPPER LEVEL JET DEVELOPS EASTWARD.

WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS THE NEXT UPPER LEVEL
SYSTEM CURRENTLY DIGGING ACROSS THE ROCKIES. AIRCRAFT AND UPPER AIR
OBSERVATIONS ACROSS WESTERN CANADA AND OVER THE NORTHEAST PACIFIC
INDICATE SOME IMPRESSIVE UPPER LEVEL WINDS...FOR THIS TIME OF
YEAR...IN EXCESS OF 110 KT WITHIN THE CORE OF THE JET STREAK
DIGGING OVER THE WESTERN CONUS. THE FIRST MID LEVEL IMPULSE IS
EXPECTED TO CONTINUE SHIFTING EASTWARD OVER THE UPPER MIDWEST INTO
MONDAY MORNING. AS IT DOES SO...IT WILL DRIVE A FAIRLY STOUT
SURFACE LOW NORTHEASTWARD FROM THE DAKOTAS TO ONTARIO. SOME VERY
SUBSTANTIAL CONVECTION IS EXPECTED TO DEVELOP AHEAD OF THE COLD
FRONT LATER TODAY ACROSS PORTIONS OF THE MID MISSOURI VALLEY AND
INTO MINNESOTA. THIS ACTIVITY WILL LIKELY SHIFT EAST-NORTHEASTWARD
OVERNIGHT TONIGHT...WITH SOME OF THE REMNANT ACTIVITY POSSIBLY
REACHING NORTH CENTRAL ILLINOIS BY AROUND...OR JUST PRIOR TO
DAYBREAK MONDAY. IT APPEARS THAT THIS INITIAL ROUND OF CONVECTION
COULD BE IN A WEAKENING PHASE AS IT TRIES TO PUSH OVER PORTIONS
OF NORTHERN ILLINOIS MONDAY MORNING. HOWEVER...RENEWED CONVECTIVE
DEVELOPMENT...POSSIBLY ALONG ANY OUTFLOW BOUNDARIES LAID DOWN BY
EARLY MORNING ACTIVITY...IS LIKELY ACROSS PORTIONS OF NORTHEASTERN
ILLINOIS AND NORTHWESTERN INDIANA BY MONDAY AFTERNOON.

MODEL SOUNDINGS ALL INDICATE FAVORABLE PROFILES FOR ACTIVE STRONG TO
SEVERE STORMS OVER THE AREA DURING THE AFTERNOON AND EARLY EVENING
MONDAY. DEEP LAYER BULK SHEAR LOOKS TO BE SOMEWHAT
UNIDIRECTIONAL...BUT WITH 0-6 KM SPEED SHEAR OF NEARLY 50
KT...ORGANIZED CONVECTIVE ACTIVITY APPEARS VERY POSSIBLE. THE MAIN
COMPLICATING FACTOR AT THIS POINT IS HOW MUCH ANY CLOUD DEBRIS OR
REMNANT MORNING CONVECTIVE ACTIVITY IMPACTS AFTERNOON HEATING AND
DESTABILIZATION ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN
INDIANA. HOWEVER...IN SPITE OF THIS POSSIBILITY EARLY IN THE
DAY...IT DOES APPEAR THAT THE HIGH THETA E NEAR SURFACE AIR MASS
SHOULD BE ENOUGH TO PRODUCE AMPLE MLCAPE VALUES AT OR JUST IN
EXCESS OF 1500 J/KG...WHICH COMBINED WITH THE 45+ DEEP LAYER SHEAR
CERTAINLY POINTS TO A SEVERE THREAT. AT THIS TIME IT APPEARS
RATHER MODEST MID LEVEL LAPSE RATES WOULD RESULT IN THE MAIN
SEVERE THREAT BEING STRONG DAMAGING WIND GUSTS. HOWEVER...THERE IS
ALSO A SECONDARY THREAT OF LARGE HAIL...ESPECIALLY IF ANY SUPER
CELLS CAN FORM.

THERE IS ALSO A DECENT CONCERN FOR EXTREMELY HEAVY RAINFALL RATES
WITH THESE STORMS...WITH PWAT VALUES IN THIS JUICY ENVIRONMENT
LIKELY TO RESIDE AROUND 1.7 INCHES. NUMERICAL GUIDANCE CONTINUES TO
SUGGEST THAT A SECONDARY MID LEVEL IMPULSE WILL APPROACH THE AREA
MONDAY NIGHT AND ACT TO INDUCE/STRENGTHEN A SOUTHWESTERLY UPPER
LEVEL JET STREAK ACROSS THE GREAT LAKES REGION INTO MONDAY NIGHT.
THIS PROCESS COULD SET UP PORTIONS OF THE AREA WITHIN THE FAVORABLE
RIGHT ENTRANCE REGION OF A 100 KT UPPER LEVEL JET INTO TUESDAY
MORNING AS THE SURFACE COLD FRONTAL BOUNDARY SLOWLY TRIES TO SHIFT
SOUTHWARD ACROSS THE SOUTHERN HALF OF MY CWA. I HAVE INCREASING
CONCERNS THAT THIS COULD SET UP A VERY HEAVY RAIN EVENT MONDAY
NIGHT...WITH STORMS POTENTIALLY TRAINING TO THE EAST NORTHEAST
NEARLY PARALLEL TO THE SURFACE BOUNDARY. AT THIS TIME IT APPEARS THIS
HEAVY RAIN THREAT COULD END UP SOUTH OF INTERSTATE 80 MONDAY NIGHT.
HOWEVER...UNCERTAINTY IS STILL A BIT HIGH AS TO HOW FAR SOUTH THE
SURFACE FRONT WILL GET MONDAY NIGHT...AND HENCE WHERE THE MOST
FAVORED AREAS FOR TRAINING CELLS WILL OCCUR. AT THIS POINT...I HAVE
ADDED HEAVY RAIN WORDING TO THE FORECAST...MAINLY FOR AREAS SOUTH OF
INTERSTATE 80 INTO MONDAY NIGHT.

FOLLOWING THIS ACTIVE WEATHER MONDAY NIGHT IT APPEARS THE WEATHER
WILL BE DRY FOR THE MOST PART THROUGH LATE WEEK. THE MAIN STORY
HOWEVER...WILL BE THE INCREASING HEAT BY THURSDAY. FORECAST GUIDANCE
CONTINUES TO FORECAST MID LEVEL HEIGHTS TO BUILD SUBSTANTIALLY
ACROSS THE CENTRAL CONUS. THIS COULD LEAD TO A RUN AT
90 TEMPERATURES FOR THURSDAY AS 850 MB TEMPERATURES WARM TO 20 TO
22C. I HAVE STARTED CUTTING BACK ON THE SLIGHT CHANCE
POPS...ESPECIALLY ON WEDNESDAY AND WEDNESDAY NIGHT...BUT LEFT IN
SOME SLIGHTS FOR THURSDAY. ALTHOUGH SOME ISOLATED CONVECTIVE
ACTIVITY IS POSSIBLE DURING THIS TIME...IT APPEARS THAT THE BUILDING
HEIGHTS AND WARMING TEMPS ALOFT COULD END UP CAPPING THE AREA...AND
LIMITING THE THREAT FOR CONVECTIVE DEVELOPMENT THROUGH THURSDAY.

CONVECTIVE CHANCES DO LOOK TO RETURN TO THE AREA AGAIN BY FRIDAY.
ANOTHER SIGNIFICANT WAVE IS EXPECTED TO SHIFT EASTWARD ACROSS THE
NORTHERN CONUS AND SOUTHERN CANADA LATE IN THE PERIOD...AND THIS
LOOKS TO SHIFT A COLD FRONT SOUTHWARD ACROSS THE AREA SOMETIME
EITHER FRIDAY OR FRIDAY NIGHT AND THIS COULD SPARK OFF ACTIVITY
ACROSS THE AREA. COOLER WEATHER DOES LOOK TO OVERSPREAD TO AREA
UNDER NORTHERLY WINDS BY EARLY NEXT WEEKEND.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310803
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CDT SUN AUG 31 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310803
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CDT SUN AUG 31 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
300 AM CDT

A PERIOD OF CHANGEABLE WEATHER...IN PARTICULAR...WIND
DIRECTION...IS SETTING UP FOR THE NEXT SEVERAL DAYS. LOW PRESSURE
JUST NORTH OF GEORGIAN BAY WILL TRACK EAST TO SOUTHERN QUEBEC BY
LATE SUNDAY MORNING WHILE DRAGGING A WEAK COLD FRONT SOUTH ACROSS
THE LAKE AND CLEARING THE SOUTH END OF LAKE MICHIGAN BY EARLY
SUNDAY. THIS WILL SET UP A BRIEF PERIOD OF NWLY WINDS...BUT AS
HIGH PRESSURE BUILDS OVER THE NORTHERN LAKES BEHIND THE FRONT
SUNDAY AFTERNOON WINDS WILL BECOME LGT/VRBL FOR A SHORT TIME.
SLY FLOW WILL RETURN TO THE LAKE SUNDAY NIGHT AND
MONDAY...STRENGTHENING TO ARND 25KT AS ANOTHER LOW DEVELOPING OVER
THE NORTHERN PLAINS DEEPENS WHILE TRACKING TO HUDSON BAY MONDAY
NIGHT. THIS LOW WILL DRAG ANOTHER COLD FRONT SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD ACROSS THE
LAKE TUESDAY BRINGING ANOTHER PERIOD OF LIGHT WINDS. BUT YET
ANOTHER LOW IS EXPECTED TO MOVE OUT OF THE NORTHERN ROCKIES AND
INTO THE NORTHERN PLAINS WEDNESDAY NIGHT...BRINGING ANOTHER PERIOD
OF BRISK SOUTH WINDS TO THE LAKE FOR WEDNESDAY AND THURSDAY. THIS
LOW IS FORECAST TO TRACK TO NEAR THE SOUTHERN TIP OF JAMES BAY
DRAGGING ANOTHER COLD FRONT ACROSS THE LAKE FRIDAY OR FRIDAY
NIGHT. ACCOMPANYING THESE FRONTAL PASSAGES WILL ALSO BE PERIODS OF
THUNDERSTORMS AS WELL.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310602
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
102 AM CDT SUN AUG 31 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310602
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
102 AM CDT SUN AUG 31 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING.

* CHANCE FOR A LAKE BREEZE/WIND SHIFT TO EASTERLY LATE SUNDAY
  AFTERNOON.

KREIN

//DISCUSSION...UPDATED 06Z...

SCT TSRA WILL CONTINUE TONIGHT WELL TO THE SOUTHEAST OF THE
TERMINALS OVER EAST CENTRAL IL AND WEST CENTRAL INDIANA. AN OLD
BOUNDARY LIES JUST SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS
HUMID AIR TO THE NORTH...MOSTLY NOTABLE IN THE DEWPOINT GRADIENT.
GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF LOW LEVEL
MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT ANTICIPATING
FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO TERMINALS.
HOWEVER...SHORT RANGE MODEL GUIDANCE IS STILL INDICATING A HIGH
POSSIBILITY OF IFR CIGS/VSBY AWAY FROM THE HIGHLY URBANIZED
AREAS...SO WILL MAINTAIN MVFR/IFR FOG AT THE MORE FOG PRONE
OUTLYING TERMINALS...PARTICULARLY GYY/DPA/RFD. ANY VSBY
RESTRICTIONS THAT DO FORM OVERNIGHT WILL QUICKLY DISSIPATE BY MID
MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE REMAINDER OF THE
DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A LAKE BREEZE TO
DEVELOP...BUT THERE APPEARS TO BE LITTLE PUSH BEHIND THE
BOUNDARY...SO AT THIS POINT...FEEL THAT CHANCES ARE LOW THAT THE
LAKE BREEZE WILL PUSH INLAND OF ORD/MDW. HOWEVER...IF THE LAKE
BREEZE DOES MANAGE TO PUSH WEST OF ORD/MDW...IT WOULD NOT BE UNTIL
ARND 22-23Z AND ELY WINDS WOULD BE ARND 5-7KT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE IN LAKE BREEZE SUNDAY AFTERNOON...AND
  MEDIUM CONFIDENCE THAT THE BOUNDARY WILL NOT PUSH THROUGH
  ORD/MDW.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 310459
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1159 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 903 PM CDT SAT AUG 30 2014

Two nearly parallel lines of isolated showers and thunderstorms,
one between I-55 & I-57 and the other near the Illinois River
(along outflow boundaries), have been weakening with the loss of
diurnal heating. This trend should continue over the next few
hours. The bulk of any overnight precipitation is expected to be
south/east of the forecast area along with the stronger deep layer
flow and moisture.

Going forecast is in pretty good shape. Only plan on a few tweaks
for the latest trends, most notably to PoPs.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1150 PM CDT SAT AUG 30 2014

Tricky aviation forecast for the first several hours of the 06Z
TAF valid time. Despite the loss of diurnal heating, convection
continues to fire along an outflow boundary from previous storms.
At this point, no terminal is immediately threatened by these
storms, though the band, and some associated outflow, is making a
gradual shift to the east. this would threaten at least KBMI
within the next few hours if they persist. Also, further east,
within a deeper moist layer, MVFR cigs have started to break out,
including at KDEC & KCMI. Have a hard time seeing how this will
improve before daybreak as slightly drier air filters in from the
west. Expect condtions to improve to or remain VFR areawide on
Saturday as the more active weather shifts off to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK






000
FXUS63 KLOT 310314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING
* CHANCE LAKE BREEZE/WIND SHIFT EASTERLY LATE SUNDAY AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT
* LOW-MEDIUM CONFIDENCE IN POTENTIAL LAKE BREEZE SUNDAY AFTERNOON
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTER-MOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING
* CHANCE LAKE BREEZE/WIND SHIFT EASTERLY LATE SUNDAY AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM-HIGH CONFIDENCE IN NO IFR AT ORD/MDW OVERNIGHT
* LOW-MEDIUM CONFIDENCE IN POTENTIAL LAKE BREEZE SUNDAY AFTERNOON
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 310213
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
913 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 903 PM CDT SAT AUG 30 2014

Two nearly parallel lines of isolated showers and thunderstorms,
one between I-55 & I-57 and the other near the Illinois River
(along outflow boundaries), have been weakening with the loss of
diurnal heating. This trend should continue over the next few
hours. The bulk of any overnight precipitation is expected to be
south/east of the forecast area along with the stronger deep layer
flow and moisture.

Going forecast is in pretty good shape. Only plan on a few tweaks
for the latest trends, most notably to PoPs.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 700 PM CDT SAT AUG 30 2014

A weak cold front cuts northeast to southwest across Illinois,
currently lying just east of KBMI & KSPI. Spotty showers/storms
are possible at all central Illinois terminals but KPIA for the
next few hours until diurnal instability is lost. Quiet/VFR
conditions are expected for he bulk of the period away from any
precipitation this evening. However, a period of MVFR fog is also
possible late tonight, as skies clear more significantly than they
have in recent days.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK






000
FXUS63 KILX 310213
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
913 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 903 PM CDT SAT AUG 30 2014

Two nearly parallel lines of isolated showers and thunderstorms,
one between I-55 & I-57 and the other near the Illinois River
(along outflow boundaries), have been weakening with the loss of
diurnal heating. This trend should continue over the next few
hours. The bulk of any overnight precipitation is expected to be
south/east of the forecast area along with the stronger deep layer
flow and moisture.

Going forecast is in pretty good shape. Only plan on a few tweaks
for the latest trends, most notably to PoPs.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 700 PM CDT SAT AUG 30 2014

A weak cold front cuts northeast to southwest across Illinois,
currently lying just east of KBMI & KSPI. Spotty showers/storms
are possible at all central Illinois terminals but KPIA for the
next few hours until diurnal instability is lost. Quiet/VFR
conditions are expected for he bulk of the period away from any
precipitation this evening. However, a period of MVFR fog is also
possible late tonight, as skies clear more significantly than they
have in recent days.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK







000
FXUS63 KILX 310004
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
704 PM CDT Sat Aug 30 2014

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 700 PM CDT SAT AUG 30 2014

A weak cold front cuts northeast to southwest across Illinois,
currently lying just east of KBMI & KSPI. Spotty showers/storms
are possible at all central Illinois terminals but KPIA for the
next few hours until diurnal instability is lost. Quiet/VFR
conditions are expected for he bulk of the period away from any
precipitation this evening. However, a period of MVFR fog is also
possible late tonight, as skies clear more significantly than they
have in recent days.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK






000
FXUS63 KILX 310004
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
704 PM CDT Sat Aug 30 2014

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 700 PM CDT SAT AUG 30 2014

A weak cold front cuts northeast to southwest across Illinois,
currently lying just east of KBMI & KSPI. Spotty showers/storms
are possible at all central Illinois terminals but KPIA for the
next few hours until diurnal instability is lost. Quiet/VFR
conditions are expected for he bulk of the period away from any
precipitation this evening. However, a period of MVFR fog is also
possible late tonight, as skies clear more significantly than they
have in recent days.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK







000
FXUS63 KLOT 302337
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
637 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CONDITIONS REMAINING VFR OVERNIGHT AND
  MEDIUM-HIGH CONFIDENCE IN NO PREVAILING IFR AT ORD/MDW OVERNIGHT
* MEDIUM CONFIDENCE IN NO WIND SHIFT TO EASTERLY WITH LAKE BREEZE
  SUNDAY AFTERNOON AT ORD/MDW
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302337
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
637 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CONDITIONS REMAINING VFR OVERNIGHT AND
  MEDIUM-HIGH CONFIDENCE IN NO PREVAILING IFR AT ORD/MDW OVERNIGHT
* MEDIUM CONFIDENCE IN NO WIND SHIFT TO EASTERLY WITH LAKE BREEZE
  SUNDAY AFTERNOON AT ORD/MDW
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302337
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
637 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CONDITIONS REMAINING VFR OVERNIGHT AND
  MEDIUM-HIGH CONFIDENCE IN NO PREVAILING IFR AT ORD/MDW OVERNIGHT
* MEDIUM CONFIDENCE IN NO WIND SHIFT TO EASTERLY WITH LAKE BREEZE
  SUNDAY AFTERNOON AT ORD/MDW
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302337
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
637 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARM UP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SLIGHT CHANCE OF FOG/STRATUS EARLY SUNDAY MORNING

IZZI

//DISCUSSION...UPDATED 00Z...

SCT`D TSRA WILL CONTINUE THIS EVENING TO THE SOUTHEAST OF THE
TERMINALS...WITH VFR CONDITIONS EXPECTED CLOSER TO THE TERMINALS.
THE TSRA ARE OCCURRING NEAR AND JUST AHEAD OF A WEAK FRONT JUST
SOUTH OF THE TERMINALS WITH SLIGHTLY DRIER/LESS HUMID AIR TO THE
NORTH OF THE FRONT. GIVEN THE LACK OF RAIN TODAY AND MIXING OUT OF
LOW LEVEL MOISTURE...PLUS THE URBAN HEAT ISLAND EFFECTS...NOT
ANTICIPATING FOG/STRATUS TO BE MUCH OF AN ISSUE FOR THE CHICAGO
TERMINALS. MODEL GUIDANCE IS STILL HITTING THE THREAT OF IFR
CIGS/VSBY PRETTY HARD...BUT CONDITIONAL CLIMO SUGGESTS THE CHANCES
OF IFR TOMORROW MORNING GIVEN CURRENT CONDITIONS IS FAR LESS THAN
10% SO HAVE GONE WITH VFR FOR MDW/ORD. MAINTAINED MVFR/IFR FOG AT
THE MORE FOG PRONE OUTLYING TERMINALS...PARTICULARLY GYY AND DPA.
ANY VSBY RESTRICTIONS/FOG THAT DOES FORM OVERNIGHT WILL QUICKLY
DISSIPATE BY MID MORNING SUNDAY WITH VFR CONDITIONS EXPECTED THE
REMAINDER OF THE DAY. WINDS SHOULD REMAIN LIGHT ENOUGH TO ALLOW A
LAKE BREEZE TO DEVELOP...BUT IF IT WERE TO THREATEN ORD/MDW IT
LIKELY WOULDN`T DO SO UNTIL VERY LATE IN THE AFTERNOON OR TOWARD
EARLY EVENING.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CONDITIONS REMAINING VFR OVERNIGHT AND
  MEDIUM-HIGH CONFIDENCE IN NO PREVAILING IFR AT ORD/MDW OVERNIGHT
* MEDIUM CONFIDENCE IN NO WIND SHIFT TO EASTERLY WITH LAKE BREEZE
  SUNDAY AFTERNOON AT ORD/MDW
* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PERIOD OR TWO OF SHRA/TSRA...STRONG TSRA POSSIBLE.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...SLIGHT CHANCE TSRA...OTHERWISE VFR.

FRIDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302213
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
513 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY WEST-SOUTHWEST WINDS DIMINISHING EARLY THIS EVENING.

* IFR CIGS AND VSBYS POSSIBLE OVERNIGHT INTO EARLY SUNDAY.

LENNING/IZZI

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* LOW-MEDIUM CONFIDENCE OF IFR CIGS AND VSBYS OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302213
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
513 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* GUSTY WEST-SOUTHWEST WINDS DIMINISHING EARLY THIS EVENING.

* IFR CIGS AND VSBYS POSSIBLE OVERNIGHT INTO EARLY SUNDAY.

LENNING/IZZI

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* LOW-MEDIUM CONFIDENCE OF IFR CIGS AND VSBYS OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 302011
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
311 PM CDT Sat Aug 30 2014

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.


&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1236 PM CDT SAT AUG 30 2014

Robust Cu-field continues to develop between the Illinois River
and I-55 early this afternoon: however, 1728z radar imagery
remains clear. As instability slowly increases, am expecting
scattered thunderstorms to develop along this corridor after
19/20z. Given timing and areal coverage uncertainties, have
included VCTS at all terminals beginning at 18z. As the afternoon
progresses, think main area of concern will shift east of the
Illinois River Valley, so have dropped VCTS at KPIA after 22z.
Further east, will maintain thunder mention through 05z, allowing
plenty of time for any diurnally driven storms to dissipate after
sunset. Once convection ends, skies will partially clear and winds
will become quite light overnight. Forecast soundings and numeric
guidance both suggest patchy fog, particularly across the western
KILX CWA where winds will be lightest. As a result, have included
reduced visbys down to 2-3sm between 09z and 13z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BARNES






000
FXUS63 KILX 302011
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
311 PM CDT Sat Aug 30 2014

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.


&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1236 PM CDT SAT AUG 30 2014

Robust Cu-field continues to develop between the Illinois River
and I-55 early this afternoon: however, 1728z radar imagery
remains clear. As instability slowly increases, am expecting
scattered thunderstorms to develop along this corridor after
19/20z. Given timing and areal coverage uncertainties, have
included VCTS at all terminals beginning at 18z. As the afternoon
progresses, think main area of concern will shift east of the
Illinois River Valley, so have dropped VCTS at KPIA after 22z.
Further east, will maintain thunder mention through 05z, allowing
plenty of time for any diurnally driven storms to dissipate after
sunset. Once convection ends, skies will partially clear and winds
will become quite light overnight. Forecast soundings and numeric
guidance both suggest patchy fog, particularly across the western
KILX CWA where winds will be lightest. As a result, have included
reduced visbys down to 2-3sm between 09z and 13z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BARNES







000
FXUS63 KLOT 301952
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
252 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NORTHWEST EXTENT OF CONVECTION WORKING INTO MDW AREA...AND WITH
  LESS LIKELIHOOD...POSSIBLY ORD AS WELL.

* GUSTY SOUTHWEST WINDS DIMINISHING THIS EVENING.

* MVFR CIGS/VSBYS AND STRONGER GUSTS NEAR STORMS.

* IFR CIGS AND VSBYS POSSIBLE OVERNIGHT INTO EARLY SUNDAY.

LENNING

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM TO LOW CONFIDENCE THAT ALL TSRA STAYS SOUTHEAST OF
  ORD/MDW TERMINALS THIS AFTERNOON...BUT GREATER CONFIDENCE THAT
  MORE WIDESPREAD ACTIVITY DOES STAY SOUTHEAST.

* MEDIUM CONFIDENCE OF IFR CIGS AND VSBYS OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301952
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
252 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NORTHWEST EXTENT OF CONVECTION WORKING INTO MDW AREA...AND WITH
  LESS LIKELIHOOD...POSSIBLY ORD AS WELL.

* GUSTY SOUTHWEST WINDS DIMINISHING THIS EVENING.

* MVFR CIGS/VSBYS AND STRONGER GUSTS NEAR STORMS.

* IFR CIGS AND VSBYS POSSIBLE OVERNIGHT INTO EARLY SUNDAY.

LENNING

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM TO LOW CONFIDENCE THAT ALL TSRA STAYS SOUTHEAST OF
  ORD/MDW TERMINALS THIS AFTERNOON...BUT GREATER CONFIDENCE THAT
  MORE WIDESPREAD ACTIVITY DOES STAY SOUTHEAST.

* MEDIUM CONFIDENCE OF IFR CIGS AND VSBYS OVERNIGHT.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 301923
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
223 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* PRIMARY CONCERN IS TIMING...EXTENT...AND DURATION OF TSRA THIS
  AFTERNOON.

LENNING

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE THAT WIDESPREAD TSRA REMAINS SOUTHEAST OF
  TERMINALS...BUT LOW CONFIDENCE OF NO TSRA AT ALL.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

* MEDIUM CONFIDENCE ON CEILING TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 301923
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
223 PM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...SCATTERED THUNDERSTORMS ARE POSSIBLE NW OF I-55 WHILE A
LINE OF STORMS WILL IMPACT AREAS ALONG AND EAST OF I-55 THROUGH THIS
EVENING. TOMORROW WILL BE DRY BUT UNSETTLED WEATHER RETURNS MONDAY
WITH MULTIPLE CHANCES FOR THUNDERSTORMS.  SEVERE STORMS ARE POSSIBLE
MONDAY. TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE PERIOD WITH A
COUPLE DAYS GETTING INTO THE MID 80S.

THROUGH TONIGHT...
AN UPPER LEVEL TROUGH IS OVER THE UPPER MISSISSIPPI RIVER VALLEY AND
IT WILL PASS OVER THE REGION THROUGH THIS EVENING. A SURFACE LOW IS
OVER THE NORTHERN END OF LAKE MI WITH ITS COLD FRONT EXTENDING
THROUGH WI AND EASTERN IA.  THE LOW WILL CONTINUE NE THROUGH THE
NIGHT.

HAVE MUCH HIGHER CONFIDENCE IN THE CONVECTIVE FORECAST TODAY
COMPARED TO YESTERDAY DUE TO CLEAR FORCING MECHANISMS.  EXPECTING TO
HAVE TWO AREAS TO MONITOR. THE FIRST IS NORTHWEST OF I-55 WHERE
ISOLATED TO SCATTERED STORMS WILL CONTINUE TO FESTER THROUGH THIS
AFTERNOON AHEAD OF UPPER LEVEL WAVE AND COLD FRONT.

THE BIGGER CONCERN WILL BE ALONG AND SE OF I-55 WHERE A LINE OF
SHOWERS AND STORMS HAS ALREADY DEVELOPED.  THE LATEST RAP ANALYSIS
SHOWS A NICE CORRIDOR OF MOISTURE CONVERGENCE WHERE THE CONVECTION
HAS FIRED.  THE LATEST AMDAR SOUNDINGS ARE CAPLESS WITH 1000-1500
J/KG OF CAPE.  HOWEVER...LAPSE RATES ARE POOR AND WIND SHEAR IS
MINIMAL AT BEST.  THE AMDAR SOUNDINGS DO HAVE LOW LEVEL INVERTED
V/S AND THE RAP ANALYSIS HAS AROUND 1000 J/KG OF DOWNDRAFT CAPE.
THEREFORE NOT EXPECTING WIDESPREAD SEVERE WEATHER...BUT A STORM OR
TWO MAY PULSE UP AND PRODUCE SEVERE WINDS.

HEAVY DOWNPOURS ARE ALSO EXPECTED WITH PWAT VALUES OF 1.6-1.8
INCHES.  BASED ON SHORT TERM GUIDANCE...THE AREA MOST CONCERNING IS
SOUTH OF A VALPARAISO IN TO GIBSON CITY IL LINE. STORMS WILL
CONTINUE TO DEVELOP AND MOVE OVER THIS REGION WITH AMPLE FORCING.
THEREFORE IF STORMS TRAIN OVER THE SAME AREA FOR AN EXTENDED PERIOD
OF TIME...FLASH FLOODING MAY OCCUR.

STORMS DIMINISH AND PUSH EAST OVERNIGHT WHILE HIGH PRESSURE SPREADS
OVER THE REGION. WINDS WILL DIMINISH AND FOG IS POSSIBLE.

SUNDAY...
SUNDAY LOOKS DRY WITH HIGH PRESSURE OVER THE REGION.  WE WILL BE IN
THE NEXT LOW/S WARM SECTOR WITH 850MB TEMPS AROUND 18C. THEREFORE
RAISED HIGH TEMPS INTO THE MID 80S AWAY FROM THE LAKE. THE WEAK
PRESSURE GRADIENT WILL ALLOW A LAKE BREEZE TO FORM AND KEEP THE IL
LAKEFRONT AROUND 80. GUIDANCE HAS SLOWED THE NEXT LOW SO PUSHED
BACK POPS SUNDAY NIGHT.

JEE

MONDAY...
UPPER WAVE DIGGING TOWARDS THE INTERMOUNTAIN WEST THIS AFTERNOON
WILL LIFT ACROSS THE PLAINS INTO THE UPPER MIDWEST ON MONDAY WITH
ATTENDANT SURFACE LOW DEEPENING AS IT LIFTS ACROSS ONTARIO TO NEAR
JAMES BAY BY LATE MONDAY. A SURFACE FRONT WILL SLOWLY PUSH ACROSS
THE REGION MONDAY AND GUIDANCE HAS TRENDED TOWARDS A SLOWER SOLUTION
OVER THE LAST 24 HOURS. MODERATE TO STRONG INSTABILITY IS PROGGED TO
DEVELOP ALONG AND AHEAD OF THE FRONT WHERE THE GFS ADVERTISES A
CORRIDOR OF JUST OVER 2000 J/KG MLCAPE JUST TO THE WEST OF THE CWA
MONDAY AFTERNOON. THE BETTER CONVERGENCE ASSOCIATED WITH THE COLD
FRONT MAY ARRIVE JUST PAST THE MOST FAVORABLE DIURNAL TIMING IF
TIMING TRENDS HOLD TRUE...BUT THE RIGHT ENTRANCE REGION TO THE UPPER
JET IS PROGGED TO MOVE OVER THE AREA BY MID TO LATE IN THE EVENING
WITH DEEP LAYER SHEAR VALUES INCREASING TO AROUND 40 KT OR SO WHICH
WOULD BE SUFFICIENT FOR AN ORGANIZED SEVERE WEATHER THREAT...THOUGH
THIS THREAT SHOULD DIMINISH WEST TO EAST AS WE GET LATER INTO THE
OVERNIGHT HOURS AND THE BOUNDARY LAYER STABILIZES.

TUESDAY THROUGH THURSDAY...
A SECONDARY SHORTWAVE TROUGH IS PROGGED TO PUSH ACROSS THE REGION ON
TUESDAY BRINGING ADDITIONAL CHANCES FOR SHOWER AND THUNDERSTORMS
MAINLY ACROSS SOUTH/SOUTHEASTERN PORTIONS OF THE CWA WHERE THE
FRONTAL BOUNDARY MAY STILL SLOWLY BE MAKING A PUSH. MODERATE TO
STRONG HEIGHTS RISES QUICKLY BUILD IN BEHIND THIS FEATURE THOUGH AND
SHOULD RESULT IN A DRY WEATHER FOR MOST OF THE FORECAST AREA
TUESDAY. THE GFS IS PARTICULAR IS HOLDING ONTO SOME POPS NORTH OF
THE BOUNDARY WEDNESDAY INTO THURSDAY WHERE PERSISTENT WARM ADVECTION
WILL RESULT IN MID LEVEL ASCENT...THOUGH THE ECMWF REMAINS DRY THIS
PERIOD. WILL MAINTAIN SLIGHT CHANCE POPS IN THE MEANTIME.

FRIDAY THROUGH SATURDAY...
THERMAL RIDGE IS EXPECTED TO MOVE BACK OVERHEAD LATE IN THE WEEK
WITH H85 TEMPS PUSHING INTO THE LOW 20C RANGE WHICH WILL LEAD TO
ANOTHER WARMUP WITH TEMPS INTO THE UPPER 80S. ANOTHER SLOW MOVING
COLD FRONT WILL THEN SAG SOUTH ACROSS THE REGION BRINGING RENEWED
CHANCES FOR SHOWERS AND THUNDERSTORMS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* PRIMARY CONCERN IS TIMING...EXTENT...AND DURATION OF TSRA THIS
  AFTERNOON.

LENNING

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE THAT WIDESPREAD TSRA REMAINS SOUTHEAST OF
  TERMINALS...BUT LOW CONFIDENCE OF NO TSRA AT ALL.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

* MEDIUM CONFIDENCE ON CEILING TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
221 PM CDT

MODERATE SOUTHWEST FLOW IS CURRENTLY IN PLACE ACROSS LAKE MICHIGAN
WHERE SOUTHWEST WINDS ARE GUSTING 20 TO 25 KTS WITH OCCASIONAL 30 KT
WINDS. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR THE NEARSHORE
WATERS THROUGH LATE THIS EVENING. THIS IS AHEAD OF LOW PRESSURE
CURRENTLY CENTERED NEAR GREEN BAY. THE LOW WILL DRAG A COLD FRONT
SOUTH ACROSS LAKE MICHIGAN TONIGHT TURNING WINDS TO THE NORTHWEST.
WINDS WILL ABATE BRIEFLY AS TRANSIENT HIGH PRESSURE PUSHES ACROSS
THE NORTHERN LAKES REGION...BUT BY MIDDAY SUNDAY WINDS ARE EXPECTED
TO BEGIN TO TURN SOUTHEAST AND START TO RAMP UP AGAIN AHEAD OF
ANOTHER AREA OF LOW PRESSURE. THIS NEXT WILL LOW LIFT FROM THE
NORTHERN PLAINS...DEEPENING AS IT HEADS TO HUDSON BAY MONDAY NIGHT
INTO TUESDAY. SOUTH WINDS ARE EXPECTED TO PEAK MONDAY OVER THE LAKE
WITH GUSTS SOLIDLY INTO THE 20 KT RANGE...APPROACHING 30 KT OVER THE
NORTH END OF THE LAKE. ANOTHER COLD FRONT WILL SAG SOUTH ACROSS LAKE
MICHIGAN MONDAY NIGHT.

DEUBELBEISS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 PM SATURDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301747
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 PM CDT SAT AUG 30 2014

.DISCUSSION...
1235 PM CDT

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE I-55 CORRIDOR. SO FAR THIS MORNING INTO
EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW CELLS
THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA.

LENNING

&&

.PREV DISCUSSION...
344 AM CDT

THE MAIN FORECAST CONCERNS WILL CENTER AROUND CONVECTIVE CHANCES AND
TIMING THROUGH THE PERIOD...ALONG WITH THE THREAT FOR STRONG TO
SEVERE CONVECTION...ESPECIALLY MONDAY.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATES TWO MID/UPPER LEVEL
DISTURBANCES OF INTEREST FOR TODAY AND TONIGHTS WEATHER. THE FIRST IS
LOCATED OVER IOWA AND INTO EXTREME NORTHERN MISSOURI...AND THIS IS
DRIVING AN AREA OF SHOWERS AND SOME EMBEDDED STORMS INTO WESTERN
ILLINOIS AT THIS HOUR. THIS WAVE IS EXPECTED TO LIFT NORTHEASTWARD
ACROSS WISCONSIN LATER THIS MORNING...AND AS IT DOES SO...A FEW
SCATTERED SHOWERS AND A THUNDERSTORM OR TWO CAN BE EXPECTED ACROSS
NORTHERN ILLINOIS. A SECOND DISTURBANCE IS CURRENTLY LOCATED ACROSS
THE EASTERN DAKOTAS SOUTHWARD INTO EASTERN NEBRASKA. THIS WAVE IS
EXPECTED TO SHIFT EASTWARD ACROSS WISCONSIN AND NORTHERN ILLINOIS
DURING THE AFTERNOON TODAY. THESE TWO DISTURBANCES WILL HELP INDUCE
A UPPER LEVEL 60+ KT SPEED MAX ACROSS THE LOWER GREAT LAKES
REGION...ESSENTIALLY SETTING UP PORTIONS OF MY AREA TO LINE UP WITHIN
THE FAVORABLE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET MAX THIS
AFTERNOON AND INTO TONIGHT. THIS SHOULD HELP TO DRIVE AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF THE AREA ALONG AND
AHEAD OF AN APPROACHING SURFACE COLD FRONT.

IT APPEARS THE BEST CHANCES FOR MORE ROBUST CONVECTIVE DEVELOPMENT
WILL BEGIN BY EARLY TO MID AFTERNOON OVER OR JUST TO THE SOUTH AND
EAST OF THE CHICAGO AREA. HIRES CONVECTIVE ALLOWING MODELS CONTINUE
TO INDICATE THE FAVORABLE LOCATIONS FOR AFTERNOON CONVECTIVE
ACTIVITY WILL PRIMARILY BE ALONG AND SOUTH OF A CHICAGO TO OTTAWA
LINE. ALTHOUGH MORNING SHOWERS AND CLOUD COVER COULD HAMPER
INSOLATION SOME ACROSS THE AREA...IT APPEARS THAT WITH DEW POINTS IN
THE LOWER 70S...MLCAPES SHOULD END UP AROUND 1500 J/KG...ESPECIALLY
ACROSS THE SOUTHEASTERN HALF OF MY AREA. THE INCREASING MID AND AN
UPPER LEVEL WIND FIELD ALSO LOOKS TO INCREASE THE DEEP LAYER SHEAR
UP TO 25 TO 30 KT...WHICH COULD SUPPORT A FEW STRONGER STORMS
CAPABLE OF STRONG WIND GUSTS. THESE STORMS WILL ALSO LIKELY PRODUCE
SOME TORRENTIAL DOWNPOURS GIVEN THE HIGH PWAT AIRMASS IN PLACE.
STORM MOTIONS OF 30 TO 40 KT SHOULD LIMIT THE RESIDENCE TIME OF
THESE STORMS OVER A GIVEN AREA...MAKING EXTREME RAINFALL AMOUNTS IN
A GIVEN AREA UNLIKELY.  THESE STORMS LOOK TO LINGER INTO THE
EVENING HOURS TONIGHT...ESPECIALLY ACROSS MY FAR SOUTHEASTERN
COUNTIES IN NORTHWESTERN INDIANA AND EAST CENTRAL ILLINOIS.

SUNDAY STILL APPEARS TO BE THE PICK DAY OF THE WEEKEND...WITH A
TEMPORARY BREAK FROM THE SHOWER AND THUNDERSTORM ACTIVITY...WHICH
WILL RETURN BY LABOR DAY. THE WEATHER PATTERN WILL BECOME ACTIVE
AGAIN EARLY NEXT WEEK AS A SIGNIFICANT UPPER LEVEL DISTURBANCE AND
ASSOCIATED SPEED MAX...EMANATING FROM THE NORTHEASTERN
PACIFIC...DIGS ACROSS THE NORTHERN CONUS. THIS LOOKS TO SUPPORT A
SURFACE LOW...WHICH SHOULD SHIFT NORTHEASTWARD ACROSS THE UPPER
MIDWEST AND INTO ONTARIO BY MONDAY. CONVECTIVE ACTIVITY...POSSIBLY
STRONG TO SEVERE WILL BE FAVORED LATE SUNDAY FROM KANSAS
NORTHEASTWARD ACROSS ACROSS IOWA AND MINNESOTA AHEAD OF AN
APPROACHING COLD FRONT. THIS COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN ILLINOIS DURING THE DAY MONDAY...AND IT APPEARS THE DIURNAL
TIMING OF THIS FRONT...AND UPPER LEVEL SYSTEM...COULD BE FAVORABLE
FOR STRONG TO SEVERE CONVECTION ACROSS THE AREA MONDAY AFTERNOON AND
EVENING...ESPECIALLY CONSIDERING THE DEEP LAYER SHEAR IS EXPECTED TO
BE MORE THAN ADEQUATE FOR ORGANIZED STRONG CONVECTION.

UNCERTAINTY INCREASES A BIT LATER MONDAY NIGHT INTO TUESDAY...AS THE
VARIOUS MODEL GUIDANCE ARE IN DISAGREEMENT IN HOW FAST THE SURFACE
COLD FRONT WILL PUSH ACROSS MY ENTIRE AREA. THE ECMWF IS SUGGESTING
A SLOWER MOVEMENT OF THE FRONTAL BOUNDARY INTO TUESDAY AS IT
SUGGESTS THAT ANOTHER MID LEVEL IMPULSE WILL SHIFT OVER THE AREA
LEADING TO THE DEVELOPMENT OF A SECONDARY SURFACE LOW OVER THE AREA.
IF THIS SOLUTION WERE TO PAN OUT...IT COULD SET THE STAGE FOR SOME
VERY HEAVY RAINFALL AMOUNTS ACROSS PORTIONS OF THE AREA INTO TUESDAY
MORNING.

DURING THE MID TO LATER PORTION OF THE WEEK IT APPEARS THINGS WILL
BE ON A WARMING TREND...ESPECIALLY BY THURSDAY AS MID LEVEL HEIGHTS
BUILD SUBSTANTIALLY ACROSS THE AREA. THIS COULD LEAD TO A RUN AT
UPPER 80 TO LOWER 90 TEMPERATURES FOR THURSDAY. I CONTINUED WITH
SLIGHT CHANCE POPS DURING THE LATER PERIOD...MAINLY DUE TO
UNCERTAINTIES ON WHETHER OR NOT ANY SMALL SCALE DISTURBANCES WILL TRY
TO SPARK OFF CONVECTION OVER THE AREA. HOWEVER...WITH THE BUILDING
HEIGHTS AND WARMING TEMPERATURES ALOFT...THE AREA COULD END UP
CAPPED TO CONVECTIVE DEVELOPMENT ON WEDNESDAY AND THURSDAY.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* PRIMARY CONCERN IS TIMING...EXTENT...AND DURATION OF TSRA THIS
  AFTERNOON.

LENNING

//DISCUSSION...UPDATED 18Z...

MODEL FORECAST DATA...SATELLITE IMAGERY...ACARS AIRCRAFT
SOUNDINGS...AND RECENT RADAR TRENDS ALL SUPPORT THE IDEA OF
INCREASED CONVECTIVE DEVELOPMENT THIS AFTERNOON...PRIMARILY
FOCUSED SOUTHEAST OF THE ORD/MDW TERMINALS. SO FAR THIS MORNING
INTO EARLY AFTERNOON THERE HAS BEEN LITTLE LIGHTNING WITH THE FEW
CELLS THAT HAVE DEVELOPED...BUT WOULD NOT BE SURPRISED TO SEE MORE
ACTIVE CONVECTION AS WE APPROACH PEAK DIURNAL HEATING. LESS
PRONOUNCED MOISTURE TRANSPORT NORTHWEST OF THIS CORRIDOR ALONG
WITH RELATIVELY WARM AIR ALOFT ARE THE FACTORS CONTRIBUTING TO
LESS CONFIDENCE OF WIDESPREAD AFTERNOON CONVECTION ACROSS THE
NORTHWEST HALF OF THE AREA...INCLUDING ORD/MDW AS WELL AS DPA AND
RFD. THE GYY TERMINAL WOULD BE ALONG THE NORTHWEST EDGE OF THE
AREA EXPECTED TO HAVE THE MORE EXTENSIVE COVERAGE.

LENNING


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE THAT WIDESPREAD TSRA REMAINS SOUTHEAST OF
  TERMINALS...BUT LOW CONFIDENCE OF NO TSRA AT ALL.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS.

* MEDIUM CONFIDENCE ON CEILING TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF ACTIVE WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. A SERIES OF WEAK LOW PRESSURE SYSTEMS WILL
TRACK ACROSS THE UPPER GREAT LAKES REGION INTO CANADA DRAGGING
WEAK COLD FRONTS ACROSS THE LAKE. MODERATE SOUTH TO SOUTHWESTERLY
WINDS WILL PERSIST ACROSS THE LAKE THROUGH MUCH OF SATURDAY UNTIL
THE FIRST OF THE COLD FRONTS SWEEPS ACROSS THE LAKE LATE THIS
AFTERNOON AND THIS EVENING...TURNING WINDS TO NORTHWESTERLY
TONIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL BRIEFLY BUILD IN
BEHIND THE FRONT...ALLOWING WINDS TO DROP OFF AND BECOME MORE
VARIABLE IN DIRECTION EARLY SUNDAY. BY SUNDAY AFTERNOON...ANOTHER
DEVELOPING LOW OVER THE NORTHERN PLAINS WILL LEAD TO STRENGTHENING
SOUTHERLY WINDS FOR MONDAY AND MONDAY EVENING...UP TO 25 KT...BUT
THE NEXT FRONT WILL CROSS THE LAKE MONDAY NIGHT. THIS FRONTAL
PASSAGE WILL NOT BE AS ABRUPT AS THE FIRST WITH WINDS ONLY VEERING
SOUTHWESTERLY. WINDS SHOULD INCREASE AGAIN TO UP TO 25KT
IMMEDIATELY FOLLOWING THE FRONTAL PASSAGE MONDAY NIGHT...BUT SHOULD
THEN WEAKEN SLIGHTLY INTO MIDWEEK WHILE REMAINING GENERALLY
SOUTHWESTERLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1236 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 1052 AM CDT SAT AUG 30 2014

Much of central Illinois remains convection-free this morning,
except for the far SE KILX CWA south of I-70 where showers and
thunderstorms are ongoing. 15z/10am visible satellite imagery is
beginning to show an enhanced band of Cu along the Illinois River
that will eventually become a broken line of thunderstorms this
afternoon. HRRR shows storms developing along the I-55 corridor
after 20z, so have adjusted PoPs accordingly. Have focused likely
PoPs along/east of I-55 by mid-afternoon into the early evening
hours. Further west, will only carry low chances along/west of the
Illinois River this afternoon, then dry by evening.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lift associated with an upper level shortwave trough over eastern
Iowa moving east-northeastward this morning is providing a focus for
a line of convection moving into western Illinois while a weaker
line of showers roughly along I-57 continues in eastern Illinois.
Cold front associated with the trough to our west is expected to
move to around to IA/IL border and stall out as the upper level
shortwave lifts northeastward bringing a continued focus for
precipitation for much of the next 24 hours. Rich moisture of close
to 2 inches will continue to stream into southeast Illinois to bring
the best chances for precipitation in that region. Tonight, as the
main trough shifts eastward, drier air continues to push eastward
allowing drier conditions to spread eastward into Illinois. As a
result, have pops trending downward overnight. Temperatures will be
down slightly today and tonight.

&&

.LONG TERM...(Sunday through Friday)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lingered a chance of showers and thunderstorms over southeast IL
Sunday where more clouds will be over eastern/se IL. Best chances of
convection will be southeast of Ohio river across KY where short
wave energy will be. Highs in the low to mid 80s Sunday (warmest
over western areas) and humid with dewpoints mostly in the lower
70s. Dry conditions across area Sunday evening then have chance of
showers and thunderstorms returning to areas nw of I-55 overnight
Sunday night. This due to approaching strong upper level trof over
Pacific Northwest that brings a cold front se through IL Monday
night. Quite warm and humid again on Monday with highs in the 80s
and dewpoints in the lower to middle 70s. Chances of showers and
thunderstorms increase from nw to se during the day Monday with
highest chances Monday afternoon/evening, gradually shifting chances
se overnight Monday night. SPC has much of central IL in a slight
chance of severe storms Monday afternoon/evening for damaging winds
and large hail. Surface to 6km bulk shear around 40 kts and CAPES
2-3K J/Kg supports this risk of severe storms from I-70 nw.

Upper level flow to become zonal by middle of next week and frontal
boundary likely not to get too far south of IL. Thus will continue
chances of showers and thunderstorms Tue with best chances (40-50%)
in southeast IL closer to frontal boundary while slight chances nw
of IL river. Just slight chances by Wed-Thu night and quite warm and
humid with highs in the mid to upper 80s and even approaching
lower 90s over southern areas Thu and Friday. This is due to
upper level ridge of 593 dm 500 mb high building over KY/TN. Next
frontal boundary to press se toward IL later Friday into Saturday
of next week increasing chances of showers and thunderstorms followed
by cooler weather next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1236 PM CDT SAT AUG 30 2014

Robust Cu-field continues to develop between the Illinois River
and I-55 early this afternoon: however, 1728z radar imagery
remains clear. As instability slowly increases, am expecting
scattered thunderstorms to develop along this corridor after
19/20z. Given timing and areal coverage uncertainties, have
included VCTS at all terminals beginning at 18z. As the afternoon
progresses, think main area of concern will shift east of the
Illinois River Valley, so have dropped VCTS at KPIA after 22z.
Further east, will maintain thunder mention through 05z, allowing
plenty of time for any diurnally driven storms to dissipate after
sunset. Once convection ends, skies will partially clear and winds
will become quite light overnight. Forecast soundings and numeric
guidance both suggest patchy fog, particularly across the western
KILX CWA where winds will be lightest. As a result, have included
reduced visbys down to 2-3sm between 09z and 13z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...BARNES









000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1236 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 1052 AM CDT SAT AUG 30 2014

Much of central Illinois remains convection-free this morning,
except for the far SE KILX CWA south of I-70 where showers and
thunderstorms are ongoing. 15z/10am visible satellite imagery is
beginning to show an enhanced band of Cu along the Illinois River
that will eventually become a broken line of thunderstorms this
afternoon. HRRR shows storms developing along the I-55 corridor
after 20z, so have adjusted PoPs accordingly. Have focused likely
PoPs along/east of I-55 by mid-afternoon into the early evening
hours. Further west, will only carry low chances along/west of the
Illinois River this afternoon, then dry by evening.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lift associated with an upper level shortwave trough over eastern
Iowa moving east-northeastward this morning is providing a focus for
a line of convection moving into western Illinois while a weaker
line of showers roughly along I-57 continues in eastern Illinois.
Cold front associated with the trough to our west is expected to
move to around to IA/IL border and stall out as the upper level
shortwave lifts northeastward bringing a continued focus for
precipitation for much of the next 24 hours. Rich moisture of close
to 2 inches will continue to stream into southeast Illinois to bring
the best chances for precipitation in that region. Tonight, as the
main trough shifts eastward, drier air continues to push eastward
allowing drier conditions to spread eastward into Illinois. As a
result, have pops trending downward overnight. Temperatures will be
down slightly today and tonight.

&&

.LONG TERM...(Sunday through Friday)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lingered a chance of showers and thunderstorms over southeast IL
Sunday where more clouds will be over eastern/se IL. Best chances of
convection will be southeast of Ohio river across KY where short
wave energy will be. Highs in the low to mid 80s Sunday (warmest
over western areas) and humid with dewpoints mostly in the lower
70s. Dry conditions across area Sunday evening then have chance of
showers and thunderstorms returning to areas nw of I-55 overnight
Sunday night. This due to approaching strong upper level trof over
Pacific Northwest that brings a cold front se through IL Monday
night. Quite warm and humid again on Monday with highs in the 80s
and dewpoints in the lower to middle 70s. Chances of showers and
thunderstorms increase from nw to se during the day Monday with
highest chances Monday afternoon/evening, gradually shifting chances
se overnight Monday night. SPC has much of central IL in a slight
chance of severe storms Monday afternoon/evening for damaging winds
and large hail. Surface to 6km bulk shear around 40 kts and CAPES
2-3K J/Kg supports this risk of severe storms from I-70 nw.

Upper level flow to become zonal by middle of next week and frontal
boundary likely not to get too far south of IL. Thus will continue
chances of showers and thunderstorms Tue with best chances (40-50%)
in southeast IL closer to frontal boundary while slight chances nw
of IL river. Just slight chances by Wed-Thu night and quite warm and
humid with highs in the mid to upper 80s and even approaching
lower 90s over southern areas Thu and Friday. This is due to
upper level ridge of 593 dm 500 mb high building over KY/TN. Next
frontal boundary to press se toward IL later Friday into Saturday
of next week increasing chances of showers and thunderstorms followed
by cooler weather next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1236 PM CDT SAT AUG 30 2014

Robust Cu-field continues to develop between the Illinois River
and I-55 early this afternoon: however, 1728z radar imagery
remains clear. As instability slowly increases, am expecting
scattered thunderstorms to develop along this corridor after
19/20z. Given timing and areal coverage uncertainties, have
included VCTS at all terminals beginning at 18z. As the afternoon
progresses, think main area of concern will shift east of the
Illinois River Valley, so have dropped VCTS at KPIA after 22z.
Further east, will maintain thunder mention through 05z, allowing
plenty of time for any diurnally driven storms to dissipate after
sunset. Once convection ends, skies will partially clear and winds
will become quite light overnight. Forecast soundings and numeric
guidance both suggest patchy fog, particularly across the western
KILX CWA where winds will be lightest. As a result, have included
reduced visbys down to 2-3sm between 09z and 13z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...BARNES








000
FXUS63 KLOT 301618
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1118 AM CDT SAT AUG 30 2014

.DISCUSSION...
344 AM CDT

THE MAIN FORECAST CONCERNS WILL CENTER AROUND CONVECTIVE CHANCES AND
TIMING THROUGH THE PERIOD...ALONG WITH THE THREAT FOR STRONG TO
SEVERE CONVECTION...ESPECIALLY MONDAY.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATES TWO MID/UPPER LEVEL
DISTURBANCES OF INTEREST FOR TODAY AND TONIGHTS WEATHER. THE FIRST IS
LOCATED OVER IOWA AND INTO EXTREME NORTHERN MISSOURI...AND THIS IS
DRIVING AN AREA OF SHOWERS AND SOME EMBEDDED STORMS INTO WESTERN
ILLINOIS AT THIS HOUR. THIS WAVE IS EXPECTED TO LIFT NORTHEASTWARD
ACROSS WISCONSIN LATER THIS MORNING...AND AS IT DOES SO...A FEW
SCATTERED SHOWERS AND A THUNDERSTORM OR TWO CAN BE EXPECTED ACROSS
NORTHERN ILLINOIS. A SECOND DISTURBANCE IS CURRENTLY LOCATED ACROSS
THE EASTERN DAKOTAS SOUTHWARD INTO EASTERN NEBRASKA. THIS WAVE IS
EXPECTED TO SHIFT EASTWARD ACROSS WISCONSIN AND NORTHERN ILLINOIS
DURING THE AFTERNOON TODAY. THESE TWO DISTURBANCES WILL HELP INDUCE
A UPPER LEVEL 60+ KT SPEED MAX ACROSS THE LOWER GREAT LAKES
REGION...ESSENTIALLY SETTING UP PORTIONS OF MY AREA TO LINE UP WITHIN
THE FAVORABLE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET MAX THIS
AFTERNOON AND INTO TONIGHT. THIS SHOULD HELP TO DRIVE AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF THE AREA ALONG AND
AHEAD OF AN APPROACHING SURFACE COLD FRONT.

IT APPEARS THE BEST CHANCES FOR MORE ROBUST CONVECTIVE DEVELOPMENT
WILL BEGIN BY EARLY TO MID AFTERNOON OVER OR JUST TO THE SOUTH AND
EAST OF THE CHICAGO AREA. HIRES CONVECTIVE ALLOWING MODELS CONTINUE
TO INDICATE THE FAVORABLE LOCATIONS FOR AFTERNOON CONVECTIVE
ACTIVITY WILL PRIMARILY BE ALONG AND SOUTH OF A CHICAGO TO OTTAWA
LINE. ALTHOUGH MORNING SHOWERS AND CLOUD COVER COULD HAMPER
INSOLATION SOME ACROSS THE AREA...IT APPEARS THAT WITH DEW POINTS IN
THE LOWER 70S...MLCAPES SHOULD END UP AROUND 1500 J/KG...ESPECIALLY
ACROSS THE SOUTHEASTERN HALF OF MY AREA. THE INCREASING MID AND AN
UPPER LEVEL WIND FIELD ALSO LOOKS TO INCREASE THE DEEP LAYER SHEAR
UP TO 25 TO 30 KT...WHICH COULD SUPPORT A FEW STRONGER STORMS
CAPABLE OF STRONG WIND GUSTS. THESE STORMS WILL ALSO LIKELY PRODUCE
SOME TORRENTIAL DOWNPOURS GIVEN THE HIGH PWAT AIRMASS IN PLACE.
STORM MOTIONS OF 30 TO 40 KT SHOULD LIMIT THE RESIDENCE TIME OF
THESE STORMS OVER A GIVEN AREA...MAKING EXTREME RAINFALL AMOUNTS IN
A GIVEN AREA UNLIKELY.  THESE STORMS LOOK TO LINGER INTO THE
EVENING HOURS TONIGHT...ESPECIALLY ACROSS MY FAR SOUTHEASTERN
COUNTIES IN NORTHWESTERN INDIANA AND EAST CENTRAL ILLINOIS.

SUNDAY STILL APPEARS TO BE THE PICK DAY OF THE WEEKEND...WITH A
TEMPORARY BREAK FROM THE SHOWER AND THUNDERSTORM ACTIVITY...WHICH
WILL RETURN BY LABOR DAY. THE WEATHER PATTERN WILL BECOME ACTIVE
AGAIN EARLY NEXT WEEK AS A SIGNIFICANT UPPER LEVEL DISTURBANCE AND
ASSOCIATED SPEED MAX...EMANATING FROM THE NORTHEASTERN
PACIFIC...DIGS ACROSS THE NORTHERN CONUS. THIS LOOKS TO SUPPORT A
SURFACE LOW...WHICH SHOULD SHIFT NORTHEASTWARD ACROSS THE UPPER
MIDWEST AND INTO ONTARIO BY MONDAY. CONVECTIVE ACTIVITY...POSSIBLY
STRONG TO SEVERE WILL BE FAVORED LATE SUNDAY FROM KANSAS
NORTHEASTWARD ACROSS ACROSS IOWA AND MINNESOTA AHEAD OF AN
APPROACHING COLD FRONT. THIS COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN ILLINOIS DURING THE DAY MONDAY...AND IT APPEARS THE DIURNAL
TIMING OF THIS FRONT...AND UPPER LEVEL SYSTEM...COULD BE FAVORABLE
FOR STRONG TO SEVERE CONVECTION ACROSS THE AREA MONDAY AFTERNOON AND
EVENING...ESPECIALLY CONSIDERING THE DEEP LAYER SHEAR IS EXPECTED TO
BE MORE THAN ADEQUATE FOR ORGANIZED STRONG CONVECTION.

UNCERTAINTY INCREASES A BIT LATER MONDAY NIGHT INTO TUESDAY...AS THE
VARIOUS MODEL GUIDANCE ARE IN DISAGREEMENT IN HOW FAST THE SURFACE
COLD FRONT WILL PUSH ACROSS MY ENTIRE AREA. THE ECMWF IS SUGGESTING
A SLOWER MOVEMENT OF THE FRONTAL BOUNDARY INTO TUESDAY AS IT
SUGGESTS THAT ANOTHER MID LEVEL IMPULSE WILL SHIFT OVER THE AREA
LEADING TO THE DEVELOPMENT OF A SECONDARY SURFACE LOW OVER THE AREA.
IF THIS SOLUTION WERE TO PAN OUT...IT COULD SET THE STAGE FOR SOME
VERY HEAVY RAINFALL AMOUNTS ACROSS PORTIONS OF THE AREA INTO TUESDAY
MORNING.

DURING THE MID TO LATER PORTION OF THE WEEK IT APPEARS THINGS WILL
BE ON A WARMING TREND...ESPECIALLY BY THURSDAY AS MID LEVEL HEIGHTS
BUILD SUBSTANTIALLY ACROSS THE AREA. THIS COULD LEAD TO A RUN AT
UPPER 80 TO LOWER 90 TEMPERATURES FOR THURSDAY. I CONTINUED WITH
SLIGHT CHANCE POPS DURING THE LATER PERIOD...MAINLY DUE TO
UNCERTAINTIES ON WHETHER OR NOT ANY SMALL SCALE DISTURBANCES WILL TRY
TO SPARK OFF CONVECTION OVER THE AREA. HOWEVER...WITH THE BUILDING
HEIGHTS AND WARMING TEMPERATURES ALOFT...THE AREA COULD END UP
CAPPED TO CONVECTIVE DEVELOPMENT ON WEDNESDAY AND THURSDAY.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* STILL CONCERNED ABOUT LOCAL TSRA TRENDS BUT ALSO NOT CONFIDENT
  ENOUGH IN TIMING OR LOCATION OR DURATION TO INCLUDE IN TAF.
  SHOWERS FORMING OVER WI ARE LIFTING NORTHEAST AND SO FAR ARE NOT
  PRODUCING LIGHTNING.

LENNING

//DISCUSSION...UPDATED 12Z...

SCT SHRA AND ISOLD TSRA CONTINUE THROUGH THE DAY TODAY AS THE AREA
REMAINS ENTRENCHED IN A WARM/MOIST AIRMASS. A WEAK COLD FRONT IS
EXPECTED TO MOVE ACROSS THE AREA TODAY IN ASSOCIATION WITH A
STRONGER UPPER LEVEL TROUGH. THE UPPER TROUGH AND SFC FRONT SHOULD
PROVIDE SOME FOCUS FOR MORE THUNDERSTORM ACTIVITY. HOWEVER...THE
TIMING OF THE FRONT WILL PLAY A SIGNIFICANT ROLE IN THE TS
COVERAGE AS IT SHOULD MOVE NRN IL BY LATE MORNING...AT A TIME
BEFORE MAX DIURNAL WARMING. THE HIGH RESOLUTION MODEL GUIDANCE
SUGGESTS THAT TS COVERAGE SHOULD INCREASE AS THE FRONT MOVES
THROUGH ECNTRL IL AND NWRN IN DURG THE EARLY AFTERNOON HOURS.
HAVE OPTED TO GO WITH THE TEMPO GROUP FOR TS FOR THE MOST
FAVORABLE TIME FOR CONVECTIVE ACTIVITY OVER THE AREA...BUT THIS IS
STILL A LOW CONFIDENCE FORECAST.

WINDS SHOULD BECOME MORE SWLY WITH GUSTS TO 15-20KT FOR THE LATE
MORNING INTO EARLY EVENING AS SOME BREAKS IN THE OVERCAST ALLOWS
FOR SOME MIXING DOWN OF STRONGER WINDS ALOFT. WINDS SHOULD DROP
OFF AND BECOME LGT/VRBL OVERNIGHT AS HIGH PRESSURE SPREADS ACROSS
THE AREA. WITH CLEARING SKIES...LIGHT WINDS AND AMPLE RESIDUAL LOW
LEVEL MOISTURE IN PLACE...THERE IS AN INCREASING CHANCE FOR FOG
AND STATUS TO DEVELOP DURG THE LATE NIGHT HOURS TONIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* LOW TO MEDIUM CONFIDENCE OF TSRA STAYING OUT OF TERMINALS.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS EXCEPT NEAR STORMS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF ACTIVE WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. A SERIES OF WEAK LOW PRESSURE SYSTEMS WILL
TRACK ACROSS THE UPPER GREAT LAKES REGION INTO CANADA DRAGGING
WEAK COLD FRONTS ACROSS THE LAKE. MODERATE SOUTH TO SOUTHWESTERLY
WINDS WILL PERSIST ACROSS THE LAKE THROUGH MUCH OF SATURDAY UNTIL
THE FIRST OF THE COLD FRONTS SWEEPS ACROSS THE LAKE LATE THIS
AFTERNOON AND THIS EVENING...TURNING WINDS TO NORTHWESTERLY
TONIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL BRIEFLY BUILD IN
BEHIND THE FRONT...ALLOWING WINDS TO DROP OFF AND BECOME MORE
VARIABLE IN DIRECTION EARLY SUNDAY. BY SUNDAY AFTERNOON...ANOTHER
DEVELOPING LOW OVER THE NORTHERN PLAINS WILL LEAD TO STRENGTHENING
SOUTHERLY WINDS FOR MONDAY AND MONDAY EVENING...UP TO 25 KT...BUT
THE NEXT FRONT WILL CROSS THE LAKE MONDAY NIGHT. THIS FRONTAL
PASSAGE WILL NOT BE AS ABRUPT AS THE FIRST WITH WINDS ONLY VEERING
SOUTHWESTERLY. WINDS SHOULD INCREASE AGAIN TO UP TO 25KT
IMMEDIATELY FOLLOWING THE FRONTAL PASSAGE MONDAY NIGHT...BUT SHOULD
THEN WEAKEN SLIGHTLY INTO MIDWEEK WHILE REMAINING GENERALLY
SOUTHWESTERLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301618
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1118 AM CDT SAT AUG 30 2014

.DISCUSSION...
344 AM CDT

THE MAIN FORECAST CONCERNS WILL CENTER AROUND CONVECTIVE CHANCES AND
TIMING THROUGH THE PERIOD...ALONG WITH THE THREAT FOR STRONG TO
SEVERE CONVECTION...ESPECIALLY MONDAY.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATES TWO MID/UPPER LEVEL
DISTURBANCES OF INTEREST FOR TODAY AND TONIGHTS WEATHER. THE FIRST IS
LOCATED OVER IOWA AND INTO EXTREME NORTHERN MISSOURI...AND THIS IS
DRIVING AN AREA OF SHOWERS AND SOME EMBEDDED STORMS INTO WESTERN
ILLINOIS AT THIS HOUR. THIS WAVE IS EXPECTED TO LIFT NORTHEASTWARD
ACROSS WISCONSIN LATER THIS MORNING...AND AS IT DOES SO...A FEW
SCATTERED SHOWERS AND A THUNDERSTORM OR TWO CAN BE EXPECTED ACROSS
NORTHERN ILLINOIS. A SECOND DISTURBANCE IS CURRENTLY LOCATED ACROSS
THE EASTERN DAKOTAS SOUTHWARD INTO EASTERN NEBRASKA. THIS WAVE IS
EXPECTED TO SHIFT EASTWARD ACROSS WISCONSIN AND NORTHERN ILLINOIS
DURING THE AFTERNOON TODAY. THESE TWO DISTURBANCES WILL HELP INDUCE
A UPPER LEVEL 60+ KT SPEED MAX ACROSS THE LOWER GREAT LAKES
REGION...ESSENTIALLY SETTING UP PORTIONS OF MY AREA TO LINE UP WITHIN
THE FAVORABLE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET MAX THIS
AFTERNOON AND INTO TONIGHT. THIS SHOULD HELP TO DRIVE AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF THE AREA ALONG AND
AHEAD OF AN APPROACHING SURFACE COLD FRONT.

IT APPEARS THE BEST CHANCES FOR MORE ROBUST CONVECTIVE DEVELOPMENT
WILL BEGIN BY EARLY TO MID AFTERNOON OVER OR JUST TO THE SOUTH AND
EAST OF THE CHICAGO AREA. HIRES CONVECTIVE ALLOWING MODELS CONTINUE
TO INDICATE THE FAVORABLE LOCATIONS FOR AFTERNOON CONVECTIVE
ACTIVITY WILL PRIMARILY BE ALONG AND SOUTH OF A CHICAGO TO OTTAWA
LINE. ALTHOUGH MORNING SHOWERS AND CLOUD COVER COULD HAMPER
INSOLATION SOME ACROSS THE AREA...IT APPEARS THAT WITH DEW POINTS IN
THE LOWER 70S...MLCAPES SHOULD END UP AROUND 1500 J/KG...ESPECIALLY
ACROSS THE SOUTHEASTERN HALF OF MY AREA. THE INCREASING MID AND AN
UPPER LEVEL WIND FIELD ALSO LOOKS TO INCREASE THE DEEP LAYER SHEAR
UP TO 25 TO 30 KT...WHICH COULD SUPPORT A FEW STRONGER STORMS
CAPABLE OF STRONG WIND GUSTS. THESE STORMS WILL ALSO LIKELY PRODUCE
SOME TORRENTIAL DOWNPOURS GIVEN THE HIGH PWAT AIRMASS IN PLACE.
STORM MOTIONS OF 30 TO 40 KT SHOULD LIMIT THE RESIDENCE TIME OF
THESE STORMS OVER A GIVEN AREA...MAKING EXTREME RAINFALL AMOUNTS IN
A GIVEN AREA UNLIKELY.  THESE STORMS LOOK TO LINGER INTO THE
EVENING HOURS TONIGHT...ESPECIALLY ACROSS MY FAR SOUTHEASTERN
COUNTIES IN NORTHWESTERN INDIANA AND EAST CENTRAL ILLINOIS.

SUNDAY STILL APPEARS TO BE THE PICK DAY OF THE WEEKEND...WITH A
TEMPORARY BREAK FROM THE SHOWER AND THUNDERSTORM ACTIVITY...WHICH
WILL RETURN BY LABOR DAY. THE WEATHER PATTERN WILL BECOME ACTIVE
AGAIN EARLY NEXT WEEK AS A SIGNIFICANT UPPER LEVEL DISTURBANCE AND
ASSOCIATED SPEED MAX...EMANATING FROM THE NORTHEASTERN
PACIFIC...DIGS ACROSS THE NORTHERN CONUS. THIS LOOKS TO SUPPORT A
SURFACE LOW...WHICH SHOULD SHIFT NORTHEASTWARD ACROSS THE UPPER
MIDWEST AND INTO ONTARIO BY MONDAY. CONVECTIVE ACTIVITY...POSSIBLY
STRONG TO SEVERE WILL BE FAVORED LATE SUNDAY FROM KANSAS
NORTHEASTWARD ACROSS ACROSS IOWA AND MINNESOTA AHEAD OF AN
APPROACHING COLD FRONT. THIS COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN ILLINOIS DURING THE DAY MONDAY...AND IT APPEARS THE DIURNAL
TIMING OF THIS FRONT...AND UPPER LEVEL SYSTEM...COULD BE FAVORABLE
FOR STRONG TO SEVERE CONVECTION ACROSS THE AREA MONDAY AFTERNOON AND
EVENING...ESPECIALLY CONSIDERING THE DEEP LAYER SHEAR IS EXPECTED TO
BE MORE THAN ADEQUATE FOR ORGANIZED STRONG CONVECTION.

UNCERTAINTY INCREASES A BIT LATER MONDAY NIGHT INTO TUESDAY...AS THE
VARIOUS MODEL GUIDANCE ARE IN DISAGREEMENT IN HOW FAST THE SURFACE
COLD FRONT WILL PUSH ACROSS MY ENTIRE AREA. THE ECMWF IS SUGGESTING
A SLOWER MOVEMENT OF THE FRONTAL BOUNDARY INTO TUESDAY AS IT
SUGGESTS THAT ANOTHER MID LEVEL IMPULSE WILL SHIFT OVER THE AREA
LEADING TO THE DEVELOPMENT OF A SECONDARY SURFACE LOW OVER THE AREA.
IF THIS SOLUTION WERE TO PAN OUT...IT COULD SET THE STAGE FOR SOME
VERY HEAVY RAINFALL AMOUNTS ACROSS PORTIONS OF THE AREA INTO TUESDAY
MORNING.

DURING THE MID TO LATER PORTION OF THE WEEK IT APPEARS THINGS WILL
BE ON A WARMING TREND...ESPECIALLY BY THURSDAY AS MID LEVEL HEIGHTS
BUILD SUBSTANTIALLY ACROSS THE AREA. THIS COULD LEAD TO A RUN AT
UPPER 80 TO LOWER 90 TEMPERATURES FOR THURSDAY. I CONTINUED WITH
SLIGHT CHANCE POPS DURING THE LATER PERIOD...MAINLY DUE TO
UNCERTAINTIES ON WHETHER OR NOT ANY SMALL SCALE DISTURBANCES WILL TRY
TO SPARK OFF CONVECTION OVER THE AREA. HOWEVER...WITH THE BUILDING
HEIGHTS AND WARMING TEMPERATURES ALOFT...THE AREA COULD END UP
CAPPED TO CONVECTIVE DEVELOPMENT ON WEDNESDAY AND THURSDAY.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* STILL CONCERNED ABOUT LOCAL TSRA TRENDS BUT ALSO NOT CONFIDENT
  ENOUGH IN TIMING OR LOCATION OR DURATION TO INCLUDE IN TAF.
  SHOWERS FORMING OVER WI ARE LIFTING NORTHEAST AND SO FAR ARE NOT
  PRODUCING LIGHTNING.

LENNING

//DISCUSSION...UPDATED 12Z...

SCT SHRA AND ISOLD TSRA CONTINUE THROUGH THE DAY TODAY AS THE AREA
REMAINS ENTRENCHED IN A WARM/MOIST AIRMASS. A WEAK COLD FRONT IS
EXPECTED TO MOVE ACROSS THE AREA TODAY IN ASSOCIATION WITH A
STRONGER UPPER LEVEL TROUGH. THE UPPER TROUGH AND SFC FRONT SHOULD
PROVIDE SOME FOCUS FOR MORE THUNDERSTORM ACTIVITY. HOWEVER...THE
TIMING OF THE FRONT WILL PLAY A SIGNIFICANT ROLE IN THE TS
COVERAGE AS IT SHOULD MOVE NRN IL BY LATE MORNING...AT A TIME
BEFORE MAX DIURNAL WARMING. THE HIGH RESOLUTION MODEL GUIDANCE
SUGGESTS THAT TS COVERAGE SHOULD INCREASE AS THE FRONT MOVES
THROUGH ECNTRL IL AND NWRN IN DURG THE EARLY AFTERNOON HOURS.
HAVE OPTED TO GO WITH THE TEMPO GROUP FOR TS FOR THE MOST
FAVORABLE TIME FOR CONVECTIVE ACTIVITY OVER THE AREA...BUT THIS IS
STILL A LOW CONFIDENCE FORECAST.

WINDS SHOULD BECOME MORE SWLY WITH GUSTS TO 15-20KT FOR THE LATE
MORNING INTO EARLY EVENING AS SOME BREAKS IN THE OVERCAST ALLOWS
FOR SOME MIXING DOWN OF STRONGER WINDS ALOFT. WINDS SHOULD DROP
OFF AND BECOME LGT/VRBL OVERNIGHT AS HIGH PRESSURE SPREADS ACROSS
THE AREA. WITH CLEARING SKIES...LIGHT WINDS AND AMPLE RESIDUAL LOW
LEVEL MOISTURE IN PLACE...THERE IS AN INCREASING CHANCE FOR FOG
AND STATUS TO DEVELOP DURG THE LATE NIGHT HOURS TONIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* LOW TO MEDIUM CONFIDENCE OF TSRA STAYING OUT OF TERMINALS.

* MEDIUM TO HIGH CONFIDENCE ON WIND TRENDS EXCEPT NEAR STORMS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF ACTIVE WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. A SERIES OF WEAK LOW PRESSURE SYSTEMS WILL
TRACK ACROSS THE UPPER GREAT LAKES REGION INTO CANADA DRAGGING
WEAK COLD FRONTS ACROSS THE LAKE. MODERATE SOUTH TO SOUTHWESTERLY
WINDS WILL PERSIST ACROSS THE LAKE THROUGH MUCH OF SATURDAY UNTIL
THE FIRST OF THE COLD FRONTS SWEEPS ACROSS THE LAKE LATE THIS
AFTERNOON AND THIS EVENING...TURNING WINDS TO NORTHWESTERLY
TONIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL BRIEFLY BUILD IN
BEHIND THE FRONT...ALLOWING WINDS TO DROP OFF AND BECOME MORE
VARIABLE IN DIRECTION EARLY SUNDAY. BY SUNDAY AFTERNOON...ANOTHER
DEVELOPING LOW OVER THE NORTHERN PLAINS WILL LEAD TO STRENGTHENING
SOUTHERLY WINDS FOR MONDAY AND MONDAY EVENING...UP TO 25 KT...BUT
THE NEXT FRONT WILL CROSS THE LAKE MONDAY NIGHT. THIS FRONTAL
PASSAGE WILL NOT BE AS ABRUPT AS THE FIRST WITH WINDS ONLY VEERING
SOUTHWESTERLY. WINDS SHOULD INCREASE AGAIN TO UP TO 25KT
IMMEDIATELY FOLLOWING THE FRONTAL PASSAGE MONDAY NIGHT...BUT SHOULD
THEN WEAKEN SLIGHTLY INTO MIDWEEK WHILE REMAINING GENERALLY
SOUTHWESTERLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 301552
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1052 AM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 1052 AM CDT SAT AUG 30 2014

Much of central Illinois remains convection-free this morning,
except for the far SE KILX CWA south of I-70 where showers and
thunderstorms are ongoing. 15z/10am visible satellite imagery is
beginning to show an enhanced band of Cu along the Illinois River
that will eventually become a broken line of thunderstorms this
afternoon. HRRR shows storms developing along the I-55 corridor
after 20z, so have adjusted PoPs accordingly. Have focused likely
PoPs along/east of I-55 by mid-afternoon into the early evening
hours. Further west, will only carry low chances along/west of the
Illinois River this afternoon, then dry by evening.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lift associated with an upper level shortwave trough over eastern
Iowa moving east-northeastward this morning is providing a focus for
a line of convection moving into western Illinois while a weaker
line of showers roughly along I-57 continues in eastern Illinois.
Cold front associated with the trough to our west is expected to
move to around to IA/IL border and stall out as the upper level
shortwave lifts northeastward bringing a continued focus for
precipitation for much of the next 24 hours. Rich moisture of close
to 2 inches will continue to stream into southeast Illinois to bring
the best chances for precipitation in that region. Tonight, as the
main trough shifts eastward, drier air continues to push eastward
allowing drier conditions to spread eastward into Illinois. As a
result, have pops trending downward overnight. Temperatures will be
down slightly today and tonight.

&&

.LONG TERM...(Sunday through Friday)
ISSUED AT 401 AM CDT SAT AUG 30 2014

Lingered a chance of showers and thunderstorms over southeast IL
Sunday where more clouds will be over eastern/se IL. Best chances of
convection will be southeast of Ohio river across KY where short
wave energy will be. Highs in the low to mid 80s Sunday (warmest
over western areas) and humid with dewpoints mostly in the lower
70s. Dry conditions across area Sunday evening then have chance of
showers and thunderstorms returning to areas nw of I-55 overnight
Sunday night. This due to approaching strong upper level trof over
Pacific Northwest that brings a cold front se through IL Monday
night. Quite warm and humid again on Monday with highs in the 80s
and dewpoints in the lower to middle 70s. Chances of showers and
thunderstorms increase from nw to se during the day Monday with
highest chances Monday afternoon/evening, gradually shifting chances
se overnight Monday night. SPC has much of central IL in a slight
chance of severe storms Monday afternoon/evening for damaging winds
and large hail. Surface to 6km bulk shear around 40 kts and CAPES
2-3K J/Kg supports this risk of severe storms from I-70 nw.

Upper level flow to become zonal by middle of next week and frontal
boundary likely not to get too far south of IL. Thus will continue
chances of showers and thunderstorms Tue with best chances (40-50%)
in southeast IL closer to frontal boundary while slight chances nw
of IL river. Just slight chances by Wed-Thu night and quite warm and
humid with highs in the mid to upper 80s and even approaching
lower 90s over southern areas Thu and Friday. This is due to
upper level ridge of 593 dm 500 mb high building over KY/TN. Next
frontal boundary to press se toward IL later Friday into Saturday
of next week increasing chances of showers and thunderstorms followed
by cooler weather next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 658 AM CDT SAT AUG 30 2014

Scattered showers continue this morning mainly east of KDEC and
could produce isolated MVFR cig/vsby. As daytime heating
begins...expecting intensification of thunderstorm activity.
Location/timing of thunderstorms still uncertain at this time so
have limited mention to VCTS after 16Z-18Z. After 00Z...drying
conditions expected to begin spreading eastward across Illinois.
Western TAF sites KPIA-KSPI likely to see fog formation overnight
while eastern TAF sites KDEC-KCMI could see continued showers
overnight until around 12Z and have left VCSH in forecast.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...BARNES
SHORT TERM...ONTON
LONG TERM...07
AVIATION...ONTON






000
FXUS63 KLOT 301422
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
922 AM CDT SAT AUG 30 2014

.DISCUSSION...
344 AM CDT

THE MAIN FORECAST CONCERNS WILL CENTER AROUND CONVECTIVE CHANCES AND
TIMING THROUGH THE PERIOD...ALONG WITH THE THREAT FOR STRONG TO
SEVERE CONVECTION...ESPECIALLY MONDAY.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATES TWO MID/UPPER LEVEL
DISTURBANCES OF INTEREST FOR TODAY AND TONIGHTS WEATHER. THE FIRST IS
LOCATED OVER IOWA AND INTO EXTREME NORTHERN MISSOURI...AND THIS IS
DRIVING AN AREA OF SHOWERS AND SOME EMBEDDED STORMS INTO WESTERN
ILLINOIS AT THIS HOUR. THIS WAVE IS EXPECTED TO LIFT NORTHEASTWARD
ACROSS WISCONSIN LATER THIS MORNING...AND AS IT DOES SO...A FEW
SCATTERED SHOWERS AND A THUNDERSTORM OR TWO CAN BE EXPECTED ACROSS
NORTHERN ILLINOIS. A SECOND DISTURBANCE IS CURRENTLY LOCATED ACROSS
THE EASTERN DAKOTAS SOUTHWARD INTO EASTERN NEBRASKA. THIS WAVE IS
EXPECTED TO SHIFT EASTWARD ACROSS WISCONSIN AND NORTHERN ILLINOIS
DURING THE AFTERNOON TODAY. THESE TWO DISTURBANCES WILL HELP INDUCE
A UPPER LEVEL 60+ KT SPEED MAX ACROSS THE LOWER GREAT LAKES
REGION...ESSENTIALLY SETTING UP PORTIONS OF MY AREA TO LINE UP WITHIN
THE FAVORABLE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET MAX THIS
AFTERNOON AND INTO TONIGHT. THIS SHOULD HELP TO DRIVE AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF THE AREA ALONG AND
AHEAD OF AN APPROACHING SURFACE COLD FRONT.

IT APPEARS THE BEST CHANCES FOR MORE ROBUST CONVECTIVE DEVELOPMENT
WILL BEGIN BY EARLY TO MID AFTERNOON OVER OR JUST TO THE SOUTH AND
EAST OF THE CHICAGO AREA. HIRES CONVECTIVE ALLOWING MODELS CONTINUE
TO INDICATE THE FAVORABLE LOCATIONS FOR AFTERNOON CONVECTIVE
ACTIVITY WILL PRIMARILY BE ALONG AND SOUTH OF A CHICAGO TO OTTAWA
LINE. ALTHOUGH MORNING SHOWERS AND CLOUD COVER COULD HAMPER
INSOLATION SOME ACROSS THE AREA...IT APPEARS THAT WITH DEW POINTS IN
THE LOWER 70S...MLCAPES SHOULD END UP AROUND 1500 J/KG...ESPECIALLY
ACROSS THE SOUTHEASTERN HALF OF MY AREA. THE INCREASING MID AND AN
UPPER LEVEL WIND FIELD ALSO LOOKS TO INCREASE THE DEEP LAYER SHEAR
UP TO 25 TO 30 KT...WHICH COULD SUPPORT A FEW STRONGER STORMS
CAPABLE OF STRONG WIND GUSTS. THESE STORMS WILL ALSO LIKELY PRODUCE
SOME TORRENTIAL DOWNPOURS GIVEN THE HIGH PWAT AIRMASS IN PLACE.
STORM MOTIONS OF 30 TO 40 KT SHOULD LIMIT THE RESIDENCE TIME OF
THESE STORMS OVER A GIVEN AREA...MAKING EXTREME RAINFALL AMOUNTS IN
A GIVEN AREA UNLIKELY.  THESE STORMS LOOK TO LINGER INTO THE
EVENING HOURS TONIGHT...ESPECIALLY ACROSS MY FAR SOUTHEASTERN
COUNTIES IN NORTHWESTERN INDIANA AND EAST CENTRAL ILLINOIS.

SUNDAY STILL APPEARS TO BE THE PICK DAY OF THE WEEKEND...WITH A
TEMPORARY BREAK FROM THE SHOWER AND THUNDERSTORM ACTIVITY...WHICH
WILL RETURN BY LABOR DAY. THE WEATHER PATTERN WILL BECOME ACTIVE
AGAIN EARLY NEXT WEEK AS A SIGNIFICANT UPPER LEVEL DISTURBANCE AND
ASSOCIATED SPEED MAX...EMANATING FROM THE NORTHEASTERN
PACIFIC...DIGS ACROSS THE NORTHERN CONUS. THIS LOOKS TO SUPPORT A
SURFACE LOW...WHICH SHOULD SHIFT NORTHEASTWARD ACROSS THE UPPER
MIDWEST AND INTO ONTARIO BY MONDAY. CONVECTIVE ACTIVITY...POSSIBLY
STRONG TO SEVERE WILL BE FAVORED LATE SUNDAY FROM KANSAS
NORTHEASTWARD ACROSS ACROSS IOWA AND MINNESOTA AHEAD OF AN
APPROACHING COLD FRONT. THIS COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN ILLINOIS DURING THE DAY MONDAY...AND IT APPEARS THE DIURNAL
TIMING OF THIS FRONT...AND UPPER LEVEL SYSTEM...COULD BE FAVORABLE
FOR STRONG TO SEVERE CONVECTION ACROSS THE AREA MONDAY AFTERNOON AND
EVENING...ESPECIALLY CONSIDERING THE DEEP LAYER SHEAR IS EXPECTED TO
BE MORE THAN ADEQUATE FOR ORGANIZED STRONG CONVECTION.

UNCERTAINTY INCREASES A BIT LATER MONDAY NIGHT INTO TUESDAY...AS THE
VARIOUS MODEL GUIDANCE ARE IN DISAGREEMENT IN HOW FAST THE SURFACE
COLD FRONT WILL PUSH ACROSS MY ENTIRE AREA. THE ECMWF IS SUGGESTING
A SLOWER MOVEMENT OF THE FRONTAL BOUNDARY INTO TUESDAY AS IT
SUGGESTS THAT ANOTHER MID LEVEL IMPULSE WILL SHIFT OVER THE AREA
LEADING TO THE DEVELOPMENT OF A SECONDARY SURFACE LOW OVER THE AREA.
IF THIS SOLUTION WERE TO PAN OUT...IT COULD SET THE STAGE FOR SOME
VERY HEAVY RAINFALL AMOUNTS ACROSS PORTIONS OF THE AREA INTO TUESDAY
MORNING.

DURING THE MID TO LATER PORTION OF THE WEEK IT APPEARS THINGS WILL
BE ON A WARMING TREND...ESPECIALLY BY THURSDAY AS MID LEVEL HEIGHTS
BUILD SUBSTANTIALLY ACROSS THE AREA. THIS COULD LEAD TO A RUN AT
UPPER 80 TO LOWER 90 TEMPERATURES FOR THURSDAY. I CONTINUED WITH
SLIGHT CHANCE POPS DURING THE LATER PERIOD...MAINLY DUE TO
UNCERTAINTIES ON WHETHER OR NOT ANY SMALL SCALE DISTURBANCES WILL TRY
TO SPARK OFF CONVECTION OVER THE AREA. HOWEVER...WITH THE BUILDING
HEIGHTS AND WARMING TEMPERATURES ALOFT...THE AREA COULD END UP
CAPPED TO CONVECTIVE DEVELOPMENT ON WEDNESDAY AND THURSDAY.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* TOUGH DECISIONS REGARDING TSRA TRENDS...TIMING...AND COVERAGE.
  DRY TAF AT ORD/MDW REFLECTS BELIEF THAT FOCUS WILL SHIFT JUST
  SOUTH AND EAST OF TERMINALS AS CHANCES INCREASE. BUT VCTS OR
  TEMPO TSRA MAY NEED TO BE REINTRODUCED. FELT A FULL DAY OF VCTS
  WOULD NOT BE HELPFUL.

LENNING

//DISCUSSION...UPDATED 12Z...

SCT SHRA AND ISOLD TSRA CONTINUE THROUGH THE DAY TODAY AS THE AREA
REMAINS ENTRENCHED IN A WARM/MOIST AIRMASS. A WEAK COLD FRONT IS
EXPECTED TO MOVE ACROSS THE AREA TODAY IN ASSOCIATION WITH A
STRONGER UPPER LEVEL TROUGH. THE UPPER TROUGH AND SFC FRONT SHOULD
PROVIDE SOME FOCUS FOR MORE THUNDERSTORM ACTIVITY. HOWEVER...THE
TIMING OF THE FRONT WILL PLAY A SIGNIFICANT ROLE IN THE TS
COVERAGE AS IT SHOULD MOVE NRN IL BY LATE MORNING...AT A TIME
BEFORE MAX DIURNAL WARMING. THE HIGH RESOLUTION MODEL GUIDANCE
SUGGESTS THAT TS COVERAGE SHOULD INCREASE AS THE FRONT MOVES
THROUGH ECNTRL IL AND NWRN IN DURG THE EARLY AFTERNOON HOURS.
HAVE OPTED TO GO WITH THE TEMPO GROUP FOR TS FOR THE MOST
FAVORABLE TIME FOR CONVECTIVE ACTIVITY OVER THE AREA...BUT THIS IS
STILL A LOW CONFIDENCE FORECAST.

WINDS SHOULD BECOME MORE SWLY WITH GUSTS TO 15-20KT FOR THE LATE
MORNING INTO EARLY EVENING AS SOME BREAKS IN THE OVERCAST ALLOWS
FOR SOME MIXING DOWN OF STRONGER WINDS ALOFT. WINDS SHOULD DROP
OFF AND BECOME LGT/VRBL OVERNIGHT AS HIGH PRESSURE SPREADS ACROSS
THE AREA. WITH CLEARING SKIES...LIGHT WINDS AND AMPLE RESIDUAL LOW
LEVEL MOISTURE IN PLACE...THERE IS AN INCREASING CHANCE FOR FOG
AND STATUS TO DEVELOP DURG THE LATE NIGHT HOURS TONIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW TO MEDIUM REGARDING CONVECTIVE TRENDS.

* MEDIUM TO HIGH REGARDING SOUTHWEST WINDS EXCEPT NEAR TSRA.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF ACTIVE WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. A SERIES OF WEAK LOW PRESSURE SYSTEMS WILL
TRACK ACROSS THE UPPER GREAT LAKES REGION INTO CANADA DRAGGING
WEAK COLD FRONTS ACROSS THE LAKE. MODERATE SOUTH TO SOUTHWESTERLY
WINDS WILL PERSIST ACROSS THE LAKE THROUGH MUCH OF SATURDAY UNTIL
THE FIRST OF THE COLD FRONTS SWEEPS ACROSS THE LAKE LATE THIS
AFTERNOON AND THIS EVENING...TURNING WINDS TO NORTHWESTERLY
TONIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL BRIEFLY BUILD IN
BEHIND THE FRONT...ALLOWING WINDS TO DROP OFF AND BECOME MORE
VARIABLE IN DIRECTION EARLY SUNDAY. BY SUNDAY AFTERNOON...ANOTHER
DEVELOPING LOW OVER THE NORTHERN PLAINS WILL LEAD TO STRENGTHENING
SOUTHERLY WINDS FOR MONDAY AND MONDAY EVENING...UP TO 25 KT...BUT
THE NEXT FRONT WILL CROSS THE LAKE MONDAY NIGHT. THIS FRONTAL
PASSAGE WILL NOT BE AS ABRUPT AS THE FIRST WITH WINDS ONLY VEERING
SOUTHWESTERLY. WINDS SHOULD INCREASE AGAIN TO UP TO 25KT
IMMEDIATELY FOLLOWING THE FRONTAL PASSAGE MONDAY NIGHT...BUT SHOULD
THEN WEAKEN SLIGHTLY INTO MIDWEEK WHILE REMAINING GENERALLY
SOUTHWESTERLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301422
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
922 AM CDT SAT AUG 30 2014

.DISCUSSION...
344 AM CDT

THE MAIN FORECAST CONCERNS WILL CENTER AROUND CONVECTIVE CHANCES AND
TIMING THROUGH THE PERIOD...ALONG WITH THE THREAT FOR STRONG TO
SEVERE CONVECTION...ESPECIALLY MONDAY.

WATER VAPOR IMAGERY EARLY THIS MORNING INDICATES TWO MID/UPPER LEVEL
DISTURBANCES OF INTEREST FOR TODAY AND TONIGHTS WEATHER. THE FIRST IS
LOCATED OVER IOWA AND INTO EXTREME NORTHERN MISSOURI...AND THIS IS
DRIVING AN AREA OF SHOWERS AND SOME EMBEDDED STORMS INTO WESTERN
ILLINOIS AT THIS HOUR. THIS WAVE IS EXPECTED TO LIFT NORTHEASTWARD
ACROSS WISCONSIN LATER THIS MORNING...AND AS IT DOES SO...A FEW
SCATTERED SHOWERS AND A THUNDERSTORM OR TWO CAN BE EXPECTED ACROSS
NORTHERN ILLINOIS. A SECOND DISTURBANCE IS CURRENTLY LOCATED ACROSS
THE EASTERN DAKOTAS SOUTHWARD INTO EASTERN NEBRASKA. THIS WAVE IS
EXPECTED TO SHIFT EASTWARD ACROSS WISCONSIN AND NORTHERN ILLINOIS
DURING THE AFTERNOON TODAY. THESE TWO DISTURBANCES WILL HELP INDUCE
A UPPER LEVEL 60+ KT SPEED MAX ACROSS THE LOWER GREAT LAKES
REGION...ESSENTIALLY SETTING UP PORTIONS OF MY AREA TO LINE UP WITHIN
THE FAVORABLE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET MAX THIS
AFTERNOON AND INTO TONIGHT. THIS SHOULD HELP TO DRIVE AN AREA OF
SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF THE AREA ALONG AND
AHEAD OF AN APPROACHING SURFACE COLD FRONT.

IT APPEARS THE BEST CHANCES FOR MORE ROBUST CONVECTIVE DEVELOPMENT
WILL BEGIN BY EARLY TO MID AFTERNOON OVER OR JUST TO THE SOUTH AND
EAST OF THE CHICAGO AREA. HIRES CONVECTIVE ALLOWING MODELS CONTINUE
TO INDICATE THE FAVORABLE LOCATIONS FOR AFTERNOON CONVECTIVE
ACTIVITY WILL PRIMARILY BE ALONG AND SOUTH OF A CHICAGO TO OTTAWA
LINE. ALTHOUGH MORNING SHOWERS AND CLOUD COVER COULD HAMPER
INSOLATION SOME ACROSS THE AREA...IT APPEARS THAT WITH DEW POINTS IN
THE LOWER 70S...MLCAPES SHOULD END UP AROUND 1500 J/KG...ESPECIALLY
ACROSS THE SOUTHEASTERN HALF OF MY AREA. THE INCREASING MID AND AN
UPPER LEVEL WIND FIELD ALSO LOOKS TO INCREASE THE DEEP LAYER SHEAR
UP TO 25 TO 30 KT...WHICH COULD SUPPORT A FEW STRONGER STORMS
CAPABLE OF STRONG WIND GUSTS. THESE STORMS WILL ALSO LIKELY PRODUCE
SOME TORRENTIAL DOWNPOURS GIVEN THE HIGH PWAT AIRMASS IN PLACE.
STORM MOTIONS OF 30 TO 40 KT SHOULD LIMIT THE RESIDENCE TIME OF
THESE STORMS OVER A GIVEN AREA...MAKING EXTREME RAINFALL AMOUNTS IN
A GIVEN AREA UNLIKELY.  THESE STORMS LOOK TO LINGER INTO THE
EVENING HOURS TONIGHT...ESPECIALLY ACROSS MY FAR SOUTHEASTERN
COUNTIES IN NORTHWESTERN INDIANA AND EAST CENTRAL ILLINOIS.

SUNDAY STILL APPEARS TO BE THE PICK DAY OF THE WEEKEND...WITH A
TEMPORARY BREAK FROM THE SHOWER AND THUNDERSTORM ACTIVITY...WHICH
WILL RETURN BY LABOR DAY. THE WEATHER PATTERN WILL BECOME ACTIVE
AGAIN EARLY NEXT WEEK AS A SIGNIFICANT UPPER LEVEL DISTURBANCE AND
ASSOCIATED SPEED MAX...EMANATING FROM THE NORTHEASTERN
PACIFIC...DIGS ACROSS THE NORTHERN CONUS. THIS LOOKS TO SUPPORT A
SURFACE LOW...WHICH SHOULD SHIFT NORTHEASTWARD ACROSS THE UPPER
MIDWEST AND INTO ONTARIO BY MONDAY. CONVECTIVE ACTIVITY...POSSIBLY
STRONG TO SEVERE WILL BE FAVORED LATE SUNDAY FROM KANSAS
NORTHEASTWARD ACROSS ACROSS IOWA AND MINNESOTA AHEAD OF AN
APPROACHING COLD FRONT. THIS COLD FRONT IS EXPECTED TO MOVE INTO
NORTHERN ILLINOIS DURING THE DAY MONDAY...AND IT APPEARS THE DIURNAL
TIMING OF THIS FRONT...AND UPPER LEVEL SYSTEM...COULD BE FAVORABLE
FOR STRONG TO SEVERE CONVECTION ACROSS THE AREA MONDAY AFTERNOON AND
EVENING...ESPECIALLY CONSIDERING THE DEEP LAYER SHEAR IS EXPECTED TO
BE MORE THAN ADEQUATE FOR ORGANIZED STRONG CONVECTION.

UNCERTAINTY INCREASES A BIT LATER MONDAY NIGHT INTO TUESDAY...AS THE
VARIOUS MODEL GUIDANCE ARE IN DISAGREEMENT IN HOW FAST THE SURFACE
COLD FRONT WILL PUSH ACROSS MY ENTIRE AREA. THE ECMWF IS SUGGESTING
A SLOWER MOVEMENT OF THE FRONTAL BOUNDARY INTO TUESDAY AS IT
SUGGESTS THAT ANOTHER MID LEVEL IMPULSE WILL SHIFT OVER THE AREA
LEADING TO THE DEVELOPMENT OF A SECONDARY SURFACE LOW OVER THE AREA.
IF THIS SOLUTION WERE TO PAN OUT...IT COULD SET THE STAGE FOR SOME
VERY HEAVY RAINFALL AMOUNTS ACROSS PORTIONS OF THE AREA INTO TUESDAY
MORNING.

DURING THE MID TO LATER PORTION OF THE WEEK IT APPEARS THINGS WILL
BE ON A WARMING TREND...ESPECIALLY BY THURSDAY AS MID LEVEL HEIGHTS
BUILD SUBSTANTIALLY ACROSS THE AREA. THIS COULD LEAD TO A RUN AT
UPPER 80 TO LOWER 90 TEMPERATURES FOR THURSDAY. I CONTINUED WITH
SLIGHT CHANCE POPS DURING THE LATER PERIOD...MAINLY DUE TO
UNCERTAINTIES ON WHETHER OR NOT ANY SMALL SCALE DISTURBANCES WILL TRY
TO SPARK OFF CONVECTION OVER THE AREA. HOWEVER...WITH THE BUILDING
HEIGHTS AND WARMING TEMPERATURES ALOFT...THE AREA COULD END UP
CAPPED TO CONVECTIVE DEVELOPMENT ON WEDNESDAY AND THURSDAY.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* TOUGH DECISIONS REGARDING TSRA TRENDS...TIMING...AND COVERAGE.
  DRY TAF AT ORD/MDW REFLECTS BELIEF THAT FOCUS WILL SHIFT JUST
  SOUTH AND EAST OF TERMINALS AS CHANCES INCREASE. BUT VCTS OR
  TEMPO TSRA MAY NEED TO BE REINTRODUCED. FELT A FULL DAY OF VCTS
  WOULD NOT BE HELPFUL.

LENNING

//DISCUSSION...UPDATED 12Z...

SCT SHRA AND ISOLD TSRA CONTINUE THROUGH THE DAY TODAY AS THE AREA
REMAINS ENTRENCHED IN A WARM/MOIST AIRMASS. A WEAK COLD FRONT IS
EXPECTED TO MOVE ACROSS THE AREA TODAY IN ASSOCIATION WITH A
STRONGER UPPER LEVEL TROUGH. THE UPPER TROUGH AND SFC FRONT SHOULD
PROVIDE SOME FOCUS FOR MORE THUNDERSTORM ACTIVITY. HOWEVER...THE
TIMING OF THE FRONT WILL PLAY A SIGNIFICANT ROLE IN THE TS
COVERAGE AS IT SHOULD MOVE NRN IL BY LATE MORNING...AT A TIME
BEFORE MAX DIURNAL WARMING. THE HIGH RESOLUTION MODEL GUIDANCE
SUGGESTS THAT TS COVERAGE SHOULD INCREASE AS THE FRONT MOVES
THROUGH ECNTRL IL AND NWRN IN DURG THE EARLY AFTERNOON HOURS.
HAVE OPTED TO GO WITH THE TEMPO GROUP FOR TS FOR THE MOST
FAVORABLE TIME FOR CONVECTIVE ACTIVITY OVER THE AREA...BUT THIS IS
STILL A LOW CONFIDENCE FORECAST.

WINDS SHOULD BECOME MORE SWLY WITH GUSTS TO 15-20KT FOR THE LATE
MORNING INTO EARLY EVENING AS SOME BREAKS IN THE OVERCAST ALLOWS
FOR SOME MIXING DOWN OF STRONGER WINDS ALOFT. WINDS SHOULD DROP
OFF AND BECOME LGT/VRBL OVERNIGHT AS HIGH PRESSURE SPREADS ACROSS
THE AREA. WITH CLEARING SKIES...LIGHT WINDS AND AMPLE RESIDUAL LOW
LEVEL MOISTURE IN PLACE...THERE IS AN INCREASING CHANCE FOR FOG
AND STATUS TO DEVELOP DURG THE LATE NIGHT HOURS TONIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW TO MEDIUM REGARDING CONVECTIVE TRENDS.

* MEDIUM TO HIGH REGARDING SOUTHWEST WINDS EXCEPT NEAR TSRA.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...PERIODS OF TSRA LIKELY.

TUESDAY...SLIGHT CHANCE TSRA EARLY.

WEDNESDAY...SLIGHT CHANCE TSRA OVERNIGHT.

THURSDAY AND FRIDAY...CHANCE TSRA.

KREIN

&&

.MARINE...
300 AM CDT

A PERIOD OF ACTIVE WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. A SERIES OF WEAK LOW PRESSURE SYSTEMS WILL
TRACK ACROSS THE UPPER GREAT LAKES REGION INTO CANADA DRAGGING
WEAK COLD FRONTS ACROSS THE LAKE. MODERATE SOUTH TO SOUTHWESTERLY
WINDS WILL PERSIST ACROSS THE LAKE THROUGH MUCH OF SATURDAY UNTIL
THE FIRST OF THE COLD FRONTS SWEEPS ACROSS THE LAKE LATE THIS
AFTERNOON AND THIS EVENING...TURNING WINDS TO NORTHWESTERLY
TONIGHT. A WEAK RIDGE OF HIGH PRESSURE WILL BRIEFLY BUILD IN
BEHIND THE FRONT...ALLOWING WINDS TO DROP OFF AND BECOME MORE
VARIABLE IN DIRECTION EARLY SUNDAY. BY SUNDAY AFTERNOON...ANOTHER
DEVELOPING LOW OVER THE NORTHERN PLAINS WILL LEAD TO STRENGTHENING
SOUTHERLY WINDS FOR MONDAY AND MONDAY EVENING...UP TO 25 KT...BUT
THE NEXT FRONT WILL CROSS THE LAKE MONDAY NIGHT. THIS FRONTAL
PASSAGE WILL NOT BE AS ABRUPT AS THE FIRST WITH WINDS ONLY VEERING
SOUTHWESTERLY. WINDS SHOULD INCREASE AGAIN TO UP TO 25KT
IMMEDIATELY FOLLOWING THE FRONTAL PASSAGE MONDAY NIGHT...BUT SHOULD
THEN WEAKEN SLIGHTLY INTO MIDWEEK WHILE REMAINING GENERALLY
SOUTHWESTERLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






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