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000
FXUS63 KLOT 282127
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
427 PM CDT SAT MAY 28 2016

.MESOSCALE DISCUSSION...
424 PM CDT

Broken line of thunderstorms moving across the Mississippi River
this hour will approach the western boundary of the forecast area
around or shortly before 600 pm CDT. Temperatures in the low to mid
80s with dewpoints into the low to mid 60s are contributing to a
corridor of around 1000 J/kg MLCAPE across northwest and north
central Illinois...however 700-500mb lapse rates are marginal around
6-6.5 C/km which will help limit the large hail threat for our area.
Deep layer shear is also on the marginal side around 30kt per latest
SPC meso-analysis. In order to see any appreciable severe weather
threat reach portions of north central Illinois would likely need to
see better cold pool development occurring within the broken line
of thunderstorms...but thus far there is no strong indication
this is occurring with upstream storms struggling due to some of
the marginal conditions. Still...DCAPE axis of 1100-1200 indicates
at least isolated microburst potential barring any better linear
organization as we head into the evening.

Deubelbeiss

&&

.SHORT TERM...
217 PM CDT

Through Sunday...

Low clouds have finally lifted Northeast of Chicago, and has
allowed for the surface to received direct light/heating. This
has pushed surface temps into the lower 80s, the abundance of low
level moisture and dewpoints in the mid 60s, will likely struggle
to allow temps to warm much more then the lower 80s. The far urban
heat island effect from the South/Southwest winds could see a few
85-86 degree values this afternoon near Chicago. Otherwise the
main concern will be on the potential for isolated severe storms
mainly along and west of interstate 39.

A decent cumulus field has developed in the wake of the lower
clouds from this morning, but vertical growth has been slow given
the weak warm layer aloft. But expect as the afternoon progresses
the vertical structure will increase allowing parcels to quickly
produce greater depth to the cumulus clouds. Further west across
Iowa is a mid-lvl wave that is helping to agitate the environment
more and producing some larger ascent and a few thunderstorms are
beginning to initiate. Most hi-resolution guidance suggests a
narrow channel of vorticity will elongate as it slips East and
become oriented from near LaCrosse WI south through West Central
IL, but as the vort lobe pushes East the depleting issue could be
the lack of direct heating and we begin to lose the diurnal
component. This could limit the severe threat further East this
evening. That being said, there is some concern that given the dew
points being anomalously high that a broken line of storms could
develop and ride East along the moist layer towards the Chicago
metro between 2-3z. The main threats/hazards for Northern Il from
any storms will likely be damaging wind gusts up to 70mph and
perhaps an isolated hail to quarter size.

Convection should quickly diminish around 4-6z, with much of the
overnight expected to be quiet and dry as a weak diffluent zone
lifts overhead. The 500mb trough axis will be steadily pivoting
East overnight, arriving overhead closer to daybreak but becoming
negatively tilted. Lapse rates will steepen by midday Sunday,
however the lack of forcing and some drier air arriving could
limit precip/convection to areas North/Northeast of Il. Have opted
to go with a dry Sunday to account for this, but could see the
need to bring back a 15-19 POP if the dry air is stubborn to
arrive. Highs will likely push back into the low 80s again Sunday.

Beachler

&&

.LONG TERM...
204 PM CDT

Sunday night through Friday...

The upper low will dampen and shift east of the region Sunday night.
Broad surface high pressure will form in its wake and bring a
generally drier start to the extended period. A subtle trough/weak
cold front will move through overnight with weak energy sliding
southeast in slightly more progressive wnw flow aloft. Most
guidance is dry with its passage but we cannot rule out an
isolated shower.

Memorial Day is shaping up to at least start off fairly nice
and stay that way for most areas in spite some increasing clouds.
After the weak trough passage, a ever so slightly cooler and less
humid airmass will remain in place. To our west warm moist
advection will resume after the gulf of Mexico is temporarily cut
off by the transient surface high. Most of the convection looks to
be tied to daytime heating. Some guidance including the GFS/GEM
attempt to bring some of this into our area. The NAM shoves the
moist airmass south suggesting a better push with the front, and
the EC keeps convection to our west. Given the mixed signals but
favoring a drier solution as is currently forecast, have trended
that direction.

Model guidance does show a diurnal weakening Monday evening, but
suggests some overnight development again to our west that will
attempt to push into our area into early Tuesday, but chances
remain tempered given the weak ridging, southeasterly drier
surface flow. Better chances for showers and thunderstorms returns
Tuesday through midweek in response to a storm system that will
move east through the Dakotas Tuesday. A warm and humid airmass
will return in the southwest flow ahead of this system with an
undisturbed feed from the gulf of Mexico. Shower and thunderstorm
chances appear highest Wednesday and Wednesday night as forcing
from the low is much closer to the region. Cooler and drier
weather will eventually take hold for the latter half of the week
as a modest cold front shifts in with dewpoints dropping back
through the 50s making it feel comfortably and seasonably cool.

KMD

&&

.AVIATION...
For the 18Z TAFs...

Sluggish low level clouds continue to show some spotty MVFR bases
across Northeast Illinois although with the surface warming the
bases have begun to lift and expect VFR conds to prevail by 20z.
Winds will continue to be breezy from the South between 10 to 15
kt with gusts between 20-25kt. To the west of the area clouds have
redeveloped with scattered showers/thunderstorms. Many of the hi-
resolution forecast guidance data suggests the earliest timing for
convection will be around 22-23z at RFD. Otherwise convection
likely will be struggling to maintain intensity or coverage as it
approaches ORD/MDW but timing for those TAF sites will be closer
to 1-2z through about 4-5z. Have opted to handle this with a VCTS
at this time as confidence remains low on coverage/intensity.

Then overnight winds will remain Southwest with a steady turn
towards West and gusty winds again for Sunday with speeds nearing
20-25kt.

Beachler

&&

.MARINE...
204 PM CDT

While fog has lifted across the lake, it is expected to return
again tonight into early Sunday, and the marine dense fog advisory
will be extended until tomorrow.

A warm front has pushed north of the lake this afternoon with
breezy southerly winds in place. The low will shift to western
Lake Superior by Sunday night, which will maintain southwest winds
to 25 kt today and to 20 kt Sunday with elevated waves on the
north half. The low will strengthen as it moves northeast to James
Bay Monday morning. A weak cold front will moves across the lake
Monday morning which will shift winds only slightly to the west
southwest, with a secondary potentially stronger cold front will
allow for a wind shift to northeast at least for the north half.
Lighter winds remain place through Tuesday before strengthening
out of the southeast in response to low pressure that will cross
the Dakotas Tuesday and move to western Lake Superior late
Wednesday.

KMD/DLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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000
FXUS63 KLOT 281931
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
231 PM CDT SAT MAY 28 2016

.SHORT TERM...
217 PM CDT

Through Sunday...

Low clouds have finally lifted Northeast of Chicago, and has
allowed for the surface to recieved direct light/heating. This has
pushed surface temps into the lower 80s, the abundance of low
level moisture and dewpoints in the mid 60s, will likely struggle
to allow temps to warm much more then the lower 80s. The far urban
heat island effect from the South/Southwest winds could see a few
85-86 degree values this afternoon near Chicago. Otherwise the
main concern will be on the potential for isolated severe storms
mainly along and west of interstate 39.

A decent cumulus field has developed in the wake of the lower
clouds from this morning, but vertical growth has been slow given
the weak warm layer aloft. But expect as the afternoon progresses
the vertical structure will increase allowing parcels to quickly
produce greater depth to the cumulus clouds. Further west across
Iowa is a mid-lvl wave that is helping to agitate the environment
more and producing some larger ascent and a few thunderstorms are
beginning to initiate. Most hi-resolution guidance suggests a
narrow channel of vorticity will elongate as it slips East and
become oriented from near LaCrosse WI south through West Central
IL, but as the vort lobe pushes East the depleting issue could be
the lack of direct heating and we begin to lose the diurnal
component. This could limit the severe threat further East this
evening. That being said, there is some concern that given the dew
points being anomalously high that a broken line of storms could
develop and ride East along the moist layer towards the Chicago
metro between 2-3z. The main threats/hazards for Northern Il from
any storms will likely be damaging wind gusts up to 70mph and
perhaps an isolated hail to quarter size.

Convection should quickly diminish around 4-6z, with much of the
overnight expected to be quiet and dry as a weak diffluent zone
lifts overhead. The 500mb trough axis will be steadily pivoting
East overnight, arriving overhead closer to daybreak but becoming
negatively tilted. Lapse rates will steepen by midday Sunday,
however the lack of forcing and some drier air arriving could
limit precip/convection to areas North/Northeast of Il. Have opted
to go with a dry Sunday to account for this, but could see the
need to bring back a 15-19 POP if the dry air is stubborn to
arrive. Highs will likely push back into the low 80s again Sunday.

Beachler

&&

.LONG TERM...
204 PM CDT

Sunday night through Friday...

The upper low will dampen and shift east of the region Sunday night.
Broad surface high pressure will form in its wake and bring a
generally drier start to the extended period. A subtle trough/weak
cold front will move through overnight with weak energy sliding
southeast in slightly more progressive wnw flow aloft. Most
guidance is dry with its passage but we cannot rule out an
isolated shower.

Memorial Day is shaping up to at least start off fairly nice
and stay that way for most areas in spite some increasing clouds.
After the weak trough passage, a ever so slightly cooler and less
humid airmass will remain in place. To our west warm moist
advection will resume after the gulf of Mexico is temporarily cut
off by the transient surface high. Most of the convection looks to
be tied to daytime heating. Some guidance including the GFS/GEM
attempt to bring some of this into our area. The NAM shoves the
moist airmass south suggesting a better push with the front, and
the EC keeps convection to our west. Given the mixed signals but
favoring a drier solution as is currently forecast, have trended
that direction.

Model guidance does show a diurnal weakening Monday evening, but
suggests some overnight development again to our west that will
attempt to push into our area into early Tuesday, but chances
remain tempered given the weak ridging, southeasterly drier
surface flow. Better chances for showers and thunderstorms returns
Tuesday through midweek in response to a storm system that will
move east through the Dakotas Tuesday. A warm and humid airmass
will return in the southwest flow ahead of this system with an
undisturbed feed from the gulf of Mexico. Shower and thunderstorm
chances appear highest Wednesday and Wednesday night as forcing
from the low is much closer to the region. Cooler and drier
weather will eventually take hold for the latter half of the week
as a modest cold front shifts in with dewpoints dropping back
through the 50s making it feel comfortably and seasonably cool.

KMD

&&

.AVIATION...
For the 18Z TAFs...

Sluggish low level clouds continue to show some spotty MVFR bases
across Northeast Illinois although with the surface warming the
bases have begun to lift and expect VFR conds to prevail by 20z.
Winds will continue to be breezy from the South between 10 to 15
kt with gusts between 20-25kt. To the west of the area clouds have
redeveloped with scattered showers/thunderstorms. Many of the hi-
resolution forecast guidance data suggests the earliest timing for
convection will be around 22-23z at RFD. Otherwise convection
likely will be struggling to maintain intensity or coverage as it
approaches ORD/MDW but timing for those TAF sites will be closer
to 1-2z through about 4-5z. Have opted to handle this with a VCTS
at this time as confidence remains low on coverage/intensity.

Then overnight winds will remain Southwest with a steady turn
towards West and gusty winds again for Sunday with speeds nearing
20-25kt.

Beachler

&&

.MARINE...
204 PM CDT

While fog has lifted across the lake, it is expected to return
again tonight into early Sunday, and the marine dense fog advisory
will be extended until tomorrow.

A warm front has pushed north of the lake this afternoon with
breezy southerly winds in place. The low will shift to western
Lake Superior by Sunday night, which will maintain southwest winds
to 25 kt today and to 20 kt Sunday with elevated waves on the
north half. The low will strengthen as it moves northeast to James
Bay Monday morning. A weak cold front will moves across the lake
monday morning which will shift winds only slightly to the west
southwest, with a secondary potentially stronger cold front will
allow for a wind shift to northeast at least for the north half.
Lighter winds remain place through Tuesday before strengthening
out of the southeast in response to low pressure that will cross
the Dakotas Tuesday and move to western Lake Superior late
Wednesday.

KMD/DLB

&&

.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/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281913
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
213 PM CDT SAT MAY 28 2016

.UPDATE...

Visible satellite imagery continues to show thick/lower clouds
lifting North across East Central Illinois towards Northeast
Illinois late this morning. Clouds have begun to thin further
West, but expect with additional heating of the surface clouds
will further erode and allow temps to quickly warm into the lower
to middle 80s. Winds will continue to be southerly to
southwesterly with speeds between 10 to 20 mph and occasional
gusts to 25 mph this afernoon. Most forecast guidance continues to
indicate minimal activity this afternoon with respect to
thunderstorms/rain coverage or development. Have held onto the
isolated coverage for this afternoon, but could easily see a dry
forecast going until closer to 7pm. The next wave will be arriving
in the western forecast area around 8 to 9 pm cdt, and will allow
for increased chances for thunderstorms in the western counties.
Although after this period and as activity works East, the
challenge will be limiting instability later this evening and
could diminish the coverage. A few of the stronger storms this
evening could be able to grow vertically enough to tap some of the
stronger winds and may be able to produce an isolated severe
storm, although this remains a very low confidence in any severe
storms. The more likelihood of storms will be a gust to 50 mph and
perhaps pea size hail.

Beachler

&&

.SHORT TERM...
306 AM CDT

Through tonight...

The main weather concerns are for the potential of some
strong thunderstorms over portions of the area...especially this
evening.

a few widely scattered showers and perhaps a thunderstorm will be
possible today. This may end up especially being the case east of I-
57 as some weak mid level disturbances shift northward over the
area. However...most areas look to be dry for much of the day...and
as a result...I have lowered POPS to just slight chances in most
areas. However...the chances of more storms will be gradually
increasing over north central and northwestern Illinois late this
afternoon...and especially this evening.

An upper level trough...currently over the Plains...will gradually
shift northeastward to the upper Mississippi Valley by this evening.
This system will likely spawn additional thunderstorms to our west
over eastern Iowa this afternoon...in close proximity to the
entrance region of an 80 KT upper level jet...and as diurnal
destabilization maximizes. This activity then looks to progress
eastward into northern Illinois into the early evening. The main
question with this activity is how far eastward will it progress
before weakening. Many of the Convective Allowing Models
(CAMs)suggest this activity will weaken quickly through the evening
as the storms shift towards northeastern Illinois. While this
certainly seems plausible given the poor diurnal timing...I still
have mentioned higher end chance POPS into the Chicago area later
this evening as I think some storms could still persist this far
east.

Some stronger storms will be possible early this
evening...especially over north central and northwestern Illinois.
Farther east...the expected weakening trend with the convection
should limit the severe threat. These storms could present a hail
risk...along with some locally strong wind gusts given the higher
DCAPE values. This activity looks to wane during the late evening
and overnight as it shifts eastward.

KJB

&&

.LONG TERM...
204 PM CDT

Sunday night through Friday...

The upper low will dampen and shift east of the region Sunday night.
Broad surface high pressure will form in its wake and bring a
generally drier start to the extended period. A subtle trough/weak
cold front will move through overnight with weak energy sliding
southeast in slightly more progressive wnw flow aloft. Most
guidance is dry with its passage but we cannot rule out an
isolated shower.

Memorial Day is shaping up to at least start off fairly nice
and stay that way for most areas in spite some increasing clouds.
After the weak trough passage, a ever so slightly cooler and less
humid airmass will remain in place. To our west warm moist
advection will resume after the gulf of Mexico is temporarily cut
off by the transient surface high. Most of the convection looks to
be tied to daytime heating. Some guidance including the GFS/GEM
attempt to bring some of this into our area. The NAM shoves the
moist airmass south suggesting a better push with the front, and
the EC keeps convection to our west. Given the mixed signals but
favoring a drier solution as is currently forecast, have trended
that direction.

Model guidance does show a diurnal weakening Monday evening, but
suggests some overnight development again to our west that will
attempt to push into our area into early Tuesday, but chances
remain tempered given the weak ridging, southeasterly drier
surface flow. Better chances for showers and thunderstorms returns
Tuesday through midweek in response to a storm system that will
move east through the Dakotas Tuesday. A warm and humid airmass
will return in the southwest flow ahead of this system with an
undisturbed feed from the gulf of Mexico. Shower and thunderstorm
chances appear highest Wednesday and Wednesday night as forcing
from the low is much closer to the region. Cooler and drier
weather will eventually take hold for the latter half of the week
as a modest cold front shifts in with dewpoints dropping back
through the 50s making it feel comfortably and seasonably cool.

KMD

&&

.AVIATION...
For the 18Z TAFs...

Sluggish low level clouds continue to show some spotty MVFR bases
across Northeast Illinois although with the surface warming the
bases have begun to lift and expect VFR conds to prevail by 20z.
Winds will continue to be breezy from the South between 10 to 15
kt with gusts between 20-25kt. To the west of the area clouds have
redeveloped with scattered showers/thunderstorms. Many of the hi-
resolution forecast guidance data suggests the earliest timing for
convection will be around 22-23z at RFD. Otherwise convection
likely will be struggling to maintain intensity or coverage as it
approaches ORD/MDW but timing for those TAF sites will be closer
to 1-2z through about 4-5z. Have opted to handle this with a VCTS
at this time as confidence remains low on coverage/intensity.

Then overnight winds will remain Southwest with a steady turn
towards West and gusty winds again for Sunday with speeds nearing
20-25kt.

Beachler

&&

.MARINE...
204 PM CDT

While fog has lifted across the lake, it is expected to return
again tonight into early Sunday, and the marine dense fog advisory
will be extended until tomorrow.

A warm front has pushed north of the lake this afternoon with
breezy southerly winds in place. The low will shift to western
Lake Superior by Sunday night, which will maintain southwest winds
to 25 kt today and to 20 kt Sunday with elevated waves on the
north half. The low will strengthen as it moves northeast to James
Bay Monday morning. A weak cold front will moves across the lake
monday morning which will shift winds only slightly to the west
southwest, with a secondary potentially stronger cold front will
allow for a wind shift to northeast at least for the north half.
Lighter winds remain place through Tuesday before strengthening
out of the southeast in response to low pressure that will cross
the Dakotas Tuesday and move to western Lake Superior late
Wednesday.

KMD/DLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Dense Fog Advisory...northern two-thirds of the open waters of
Lake Michigan through Sunday mid-afternoon.

&&

$$

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 281147
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
647 AM CDT SAT MAY 28 2016

.SHORT TERM...
306 AM CDT

Through tonight...

The main weather concerns are for the potential of some
strong thunderstorms over portions of the area...especially this
evening.

a few widely scattered showers and perhaps a thunderstorm will be
possible today. This may end up especially being the case east of I-
57 as some weak mid level disturbances shift northward over the
area. However...most areas look to be dry for much of the day...and
as a result...I have lowered POPS to just slight chances in most
areas. However...the chances of more storms will be gradually
increasing over north central and northwestern Illinois late this
afternoon...and especially this evening.

An upper level trough...currently over the Plains...will gradually
shift northeastward to the upper Mississippi Valley by this evening.
This system will likely spawn additional thunderstorms to our west
over eastern Iowa this afternoon...in close proximity to the
entrance region of an 80 KT upper level jet...and as diurnal
destabilization maximizes. This activity then looks to progress
eastward into northern Illinois into the early evening. The main
question with this activity is how far eastward will it progress
before weakening. Many of the Convective Allowing Models
(CAMs)suggest this activity will weaken quickly through the evening
as the storms shift towards northeastern Illinois. While this
certainly seems plausible given the poor diurnal timing...I still
have mentioned higher end chance POPS into the Chicago area later
this evening as I think some storms could still persist this far
east.

Some stronger storms will be possible early this
evening...especially over north central and northwestern Illinois.
Farther east...the expected weakening trend with the convection
should limit the severe threat. These storms could present a hail
risk...along with some locally strong wind gusts given the higher
DCAPE values. This activity looks to wane during the late evening
and overnight as it shifts eastward.

KJB

&&

.LONG TERM...
345 AM CDT

Sunday through Friday...

The upper trough mentioned above will shift over southern WI and
northern IL by midday Sunday. This should help drive some
scattered diurnal shower and storm development again on Sunday.
However...at this time it appears the best chance of storms may
remain to our north in WI...but we cannot rule out a few storms
getting as far south as northern Illinois. Otherwise...Sunday is
looking dry for most areas...with temperatures again getting into
the lower 80s.

Our next good chance of showers and storms looks to enter the
picture for Tuesday and Wednesday. Model guidance/ensembles are in
good agreement with the development of another storm system over the
Dakotas into the Upper Midwest by Tuesday. This storm system looks
to push a cold front across the area by Wednesday evening. A period
or two of thunderstorms will be possible over the area ahead of
this frontal boundary. However...once it passes Wednesday
night...the threat of precip will come to an end...with the rest
of the week looking to be on the dry and cooler side.

KJB

&&

.AVIATION...
For the 12Z TAFs...

Main aviation concerns continue to be timing the greatest threat
of thunderstorms across the terminals late today/this evening...in
addition to gusty south winds through the day.

Low pressure over the mid-Missouri valley will lift northeast
across the upper Midwest through tonight. Warm...moist and
conditionally unstable air will continue to feed into the region
on gusty south winds...20-25 kts through this afternoon. While
isolated to scattered shra/tsra can not be ruled out during the
day...the best organized large scale forcing for higher coverage
tsra is expected to be late this afternoon and this evening.
Trends from various convective-allowing model runs continue to
suggest that tsra will develop across parts of eastern Iowa...
southwest WI and western IL later this afternoon...spreading
eastward into north central IL by early evening and into the
Chicago area mid-late evening. Guidance trends also indicate that
storms will likely be diminishing/decaying as they move east away
from the stronger large scale forcing as well as with diminishing
instability after sunset. Thus have carried a tempo for tsra at
KRFD early in the evening...and maintained prob30 mention for
Chicago area taf sites given less confidence of storms directlyimpacting
the eastern terminals. Activity should be greatly diminished or
ending by the 06z time frame.

Otherwise...gusty southerly surface winds are expected through
the day in the region of tight surface pressure gradient east of
the low. Forecast soundings support gusts of 20-25 kt...perhaps a
bit higher at times if boundary layer mixes as deeply as some
guidance indicates.

Ratzer

&&

.MARINE...
214 AM CDT

Relatively quiet period for marine weather...with the only issues
being some lingering dense fog over northern parts of the lake and
breezy south winds today and tonight. No recent visibility
observations...though model forecasts indicate fog should become
less widespread with time this morning/today. Will maintain
current dense fog advisory into this afternoon... though would
expect it could be cancelled earlier.

A diffuse area of low pressure was over the central Plains early
this morning...with a warm front arcing across the upper Midwest
and about two thirds of the way up the lake. This low will lift
slowly to the northeast over the weekend...reaching the upper
Mississippi Valley by this evening and moving across far western
Lake Superior by early Sunday. As the low...and the warm front...
move north...winds will shift to the south across the lake. Winds
will gust into the 20-25 kt range today...and 15-20 kt later
tonight and Sunday. Winds across WI and IL will shift west-
southwest behind a cold front on Sunday with gusts 20-25 kt also
affecting the immediate western shore of the lake. Cool water and
warm air will make for a stable marine boundary layer over the
open waters resulting in lighter winds away from shore especially
on the southern part of the lake. The low will continue to pull
slowly away to the northeast of the Great Lakes early next week
with a weaker surface pressure gradient across the lakes bringing
lighter winds. Another low may lift across the upper Midwest mid-
week...with another frontal passage Wednesday or Wednesday night.

Ratzer

&&

.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/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 280846
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
346 AM CDT SAT MAY 28 2016

.SHORT TERM...
306 AM CDT

Through tonight...

The main weather concerns are for the potential of some
strong thunderstorms over portions of the area...especially this
evening.

a few widely scattered showers and perhaps a thunderstorm will be
possible today. This may end up especially being the case east of I-
57 as some weak mid level disturbances shift northward over the
area. However...most areas look to be dry for much of the day...and
as a result...I have lowered POPS to just slight chances in most
areas. However...the chances of more storms will be gradually
increasing over north central and northwestern Illinois late this
afternoon...and especially this evening.

An upper level trough...currently over the Plains...will gradually
shift northeastward to the upper Mississippi Valley by this evening.
This system will likely spawn additional thunderstorms to our west
over eastern Iowa this afternoon...in close proximity to the
entrance region of an 80 KT upper level jet...and as diurnal
destabilization maximizes. This activity then looks to progress
eastward into northern Illinois into the early evening. The main
question with this activity is how far eastward will it progress
before weakening. Many of the Convective Allowing Models
(CAMs)suggest this activity will weaken quickly through the evening
as the storms shift towards northeastern Illinois. While this
certainly seems plausible given the poor diurnal timing...I still
have mentioned higher end chance POPS into the Chicago area later
this evening as I think some storms could still persist this far
east.

Some stronger storms will be possible early this
evening...especially over north central and northwestern Illinois.
Farther east...the expected weakening trend with the convection
should limit the severe threat. These storms could present a hail
risk...along with some locally strong wind gusts given the higher
DCAPE values. This activity looks to wane during the late evening
and overnight as it shifts eastward.

KJB

&&

.LONG TERM...
345 AM CDT

Sunday through Friday...

The upper trough mentioned above will shift over southern WI and
northern IL by midday Sunday. This should help drive some
scattered diurnal shower and storm development again on Sunday.
However...at this time it appears the best chance of storms may
remain to our north in WI...but we cannot rule out a few storms
getting as far south as northern Illinois. Otherwise...Sunday is
looking dry for most areas...with temperatures again getting into
the lower 80s.

Our next good chance of showers and storms looks to enter the
picture for Tuesday and Wednesday. Model guidance/ensembles are in
good agreement with the development of another storm system over the
Dakotas into the Upper Midwest by Tuesday. This storm system looks
to push a cold front across the area by Wednesday evening. A period
or two of thunderstorms will be possible over the area ahead of
this frontal boundary. However...once it passes Wednesday
night...the threat of precip will come to an end...with the rest
of the week looking to be on the dry and cooler side.

KJB

&&

.AVIATION...
For the 06Z TAFs...

The main concern through the TAF period is with timing the
potential for thunderstorms.

Deep south-southwest flow will persist across the area through
Saturday evening...with warm...moist air mass remaining in place
across the terminals. Forecast soundings indicate this air mass
will become conditionally unstable by this afternoon...with a low
potential for isolated shra/tsra hard to rule out at any particular
time given the potential for subtle minor amplitude mid-level
disturbances to ripple northward ahead of a deeper upper trough
over the central Plains. It appears that Saturday evening will see
the greatest potential for more organized shra/tsra however...as a
stronger mid-level disturbance wraps around the base of the trough
to the west of the area and rotates northeastward into the upper
Midwest. With late afternoon and early evening peak in diurnal
instability and aforementioned forcing aloft...model guidance has
been relatively consistent in depicting thunderstorm development
to the west of the terminals across eastern IA..southwest WI and
western IL. KRFD...in closer proximity to convective development
late in the afternoon likely has a bit higher threat of tsra by
early evening. Threat for Chicago area terminals appears to be
more mid-late evening with model guidance indicating an decaying
line of tsra approaching by 03-04z. While signal for decaying
convection farther to the east is consistent with several models
and over successive runs...forecast soundings indicate sufficient
instability for tsra to continue to move east into Chicago area
should an organized outflow or MCV provide forcing for continued
eastward development. Brief MVFR cig/vis conditions would be
likely with thunderstorms.

Otherwise...south winds will likely gust 20-25 kts later this
morning through this afternoon.

Ratzer

&&

.MARINE...
214 AM CDT

Relatively quiet period for marine weather...with the only issues
being some lingering dense fog over northern parts of the lake and
breezy south winds today and tonight. No recent visibility
observations...though model forecasts indicate fog should become
less widespread with time this morning/today. Will maintain
current dense fog advisory into this afternoon... though would
expect it could be cancelled earlier.

A diffuse area of low pressure was over the central Plains early
this morning...with a warm front arcing across the upper Midwest
and about two thirds of the way up the lake. This low will lift
slowly to the northeast over the weekend...reaching the upper
Mississippi Valley by this evening and moving across far western
Lake Superior by early Sunday. As the low...and the warm front...
move north...winds will shift to the south across the lake. Winds
will gust into the 20-25 kt range today...and 15-20 kt later
tonight and Sunday. Winds across WI and IL will shift west-
southwest behind a cold front on Sunday with gusts 20-25 kt also
affecting the immediate western shore of the lake. Cool water and
warm air will make for a stable marine boundary layer over the
open waters resulting in lighter winds away from shore especially
on the southern part of the lake. The low will continue to pull
slowly away to the northeast of the Great Lakes early next week
with a weaker surface pressure gradient across the lakes bringing
lighter winds. Another low may lift across the upper Midwest mid-
week...with another frontal passage Wednesday or Wednesday night.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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000
FXUS63 KLOT 280806
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
306 AM CDT SAT MAY 28 2016


.SHORT TERM...
306 AM CDT

Through tonight...

The main weather concerns are for the potential of some
strong thunderstorms over portions of the area...especially this
evening.

a few widely scattered showers and perhaps a thunderstorm will be
possible today. This may end up especially being the case east of I-
57 as some weak mid level disturbances shift northward over the
area. However...most areas look to be dry for much of the day...and
as a result...I have lowered POPS to just slight chances in most
areas. However...the chances of more storms will be gradually
increasing over north central and northwestern Illinois late this
afternoon...and especially this evening.

An upper level trough...currently over the Plains...will gradually
shift northeastward to the upper Mississippi Valley by this evening.
This system will likely spawn additional thunderstorms to our west
over eastern Iowa this afternoon...in close proximity to the
entrance region of an 80 KT upper level jet...and as diurnal
destabilization maximizes. This activity then looks to progress
eastward into northern Illinois into the early evening. The main
question with this activity is how far eastward will it progress
before weakening. Many of the Convective Allowing Models
(CAMs)suggest this activity will weaken quickly through the evening
as the storms shift towards northeastern Illinois. While this
certainly seems plausible given the poor diurnal timing...I still
have mentioned higher end chance POPS into the Chicago area later
this evening as I think some storms could still persist this far
east.

Some stronger storms will be possible early this
evening...especially over north central and northwestern Illinois.
Farther east...the expected weakening trend with the convection
should limit the severe threat. These storms could present a hail
risk...along with some locally strong wind gusts given the higher
DCAPE values. This activity looks to wane during the late evening
and overnight as it shifts eastward.

KJB

&&

.LONG TERM...
300 PM CDT

Tomorrow through Friday...

The pattern remains active through late next week. Confidence in day
to day convection is not overly high because forcing is weak in most
cases. The atmosphere looks relatively primed for convection,
especially in the near term, but have less confidence in forcing.
Confidence decreases rapidly Thursday night through next Friday due
to model differences.  Highs will remain in the 80s through most of
next week. Lake breezes are possible next week leading to highs in
the upper 60s along the lake.

Saturday is looking very similar to today as far as precip is
concerned. A weak vort streamer lifts north through the day and
expecting convection to increase in coverage to scattered in the
afternoon. Kept PoPs in the generic chance range since the pop up
convection will be hard to catch deterministically in the grids.
Main threat will be heavy rain and perhaps a few will produce gusty
winds. CAPE values look to be less than 1000 J/kg with weak shear.
Pwat values remain high though around 1.75 inches. Storm motion
looks a little better with southwest to northeast movement at around
30-40 kt.

Convection dies off diurnally Saturday night...but left over
convection from the west shifts east through the night. Expecting
the storms to diminish as they do so. Could see some gusty winds as
the storms first breach the western CWA, as depicted by SPC`s day 2
marginal risk.  Areas along and west of I-39 are included in the
marginal risk.

Guidance differs more than I would like with the main upper level
trough Sunday. The GFS is further south than the other models and
thinking precip will be closely tied to the trough. The better storm
coverage will be over Wisconsin...but storms are possible mainly
north and along I-88. Kept a slight chance along and north of I-80
in case the GFS is right. Lifted Pops even further north Sunday
afternoon as the trough lifts northeast with a slight chance along
the IL/WI state line and east of I-55.  CAPE values are forecast to
be below 1000 J/kg again with even weaker shear so not expecting any
severe storms.  Forecast Pwat values are around an inch...but
thinking storms still may produce heavy rain.

We get a break in convection Sunday night through Monday morning!
The GFS and ECMWF bring convection associated with a shortwave into
north central IL Monday afternoon. Have medium-low confidence in the
convection making it into the CWA so capped PoPs in the low chance
range. The GFS is more aggressive than the ECMWF so also limited how
far east the precip gets.  Monday should be mainly dry for most if
not all locations.

Tuesday may be dry, but the GFS features some upper level vort
streamers that may help convection get going. Kept a chance of
thunderstorms in the forecast but have low confidence in PoPs
through the afternoon. Guidance is consistent with additional
convection proceeding an approaching cold front passing through
Wednesday night and Thursday. The GFS is still the most aggressive
with the precip since it has a stronger second upper level low
pressure trough over the plains.  Have low confidence in PoPs
Thursday night into Friday given the drastic differences in
guidance`s upper level patterns. The GFS has a cutoff low over
Kansas while the ECMWF has a closed low over Ontario and a trough
axis moving through the region late it in the week.  Moral of the
story is the pattern remains busy but exact details mid to late next
week are very fuzzy.  Temps in the 80s look solid...with a psbl cool
down into the 70s late next week.

JEE

&&

.AVIATION...
For the 06Z TAFs...

The main concern through the TAF period is with timing the
potential for thunderstorms.

Deep south-southwest flow will persist across the area through
Saturday evening...with warm...moist air mass remaining in place
across the terminals. Forecast soundings indicate this air mass
will become conditionally unstable by this afternoon...with a low
potential for isolated shra/tsra hard to rule out at any particular
time given the potential for subtle minor amplitude mid-level
disturbances to ripple northward ahead of a deeper upper trough
over the central Plains. It appears that Saturday evening will see
the greatest potential for more organized shra/tsra however...as a
stronger mid-level disturbance wraps around the base of the trough
to the west of the area and rotates northeastward into the upper
Midwest. With late afternoon and early evening peak in diurnal
instability and aforementioned forcing aloft...model guidance has
been relatively consistent in depicting thunderstorm development
to the west of the terminals across eastern IA..southwest WI and
western IL. KRFD...in closer proximity to convective development
late in the afternoon likely has a bit higher threat of tsra by
early evening. Threat for Chicago area terminals appears to be
more mid-late evening with model guidance indicating an decaying
line of tsra approaching by 03-04z. While signal for decaying
convection farther to the east is consistent with several models
and over successive runs...forecast soundings indicate sufficient
instability for tsra to continue to move east into Chicago area
should an organized outflow or MCV provide forcing for continued
eastward development. Brief MVFR cig/vis conditions would be
likely with thunderstorms.

Otherwise...south winds will likely gust 20-25 kts later this
morning through this afternoon.

Ratzer

&&

.MARINE...
214 AM CDT

Relatively quiet period for marine weather...with the only issues
being some lingering dense fog over northern parts of the lake and
breezy south winds today and tonight. No recent visibility
observations...though model forecasts indicate fog should become
less widespread with time this morning/today. Will maintain
current dense fog advisory into this afternoon... though would
expect it could be cancelled earlier.

A diffuse area of low pressure was over the central Plains early
this morning...with a warm front arcing across the upper Midwest
and about two thirds of the way up the lake. This low will lift
slowly to the northeast over the weekend...reaching the upper
Mississippi Valley by this evening and moving across far western
Lake Superior by early Sunday. As the low...and the warm front...
move north...winds will shift to the south across the lake. Winds
will gust into the 20-25 kt range today...and 15-20 kt later
tonight and Sunday. Winds across WI and IL will shift west-
southwest behind a cold front on Sunday with gusts 20-25 kt also
affecting the immediate western shore of the lake. Cool water and
warm air will make for a stable marine boundary layer over the
open waters resulting in lighter winds away from shore especially
on the southern part of the lake. The low will continue to pull
slowly away to the northeast of the Great Lakes early next week
with a weaker surface pressure gradient across the lakes bringing
lighter winds. Another low may lift across the upper Midwest mid-
week...with another frontal passage Wednesday or Wednesday night.

Ratzer

&&

.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:
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 280714
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
214 AM CDT SAT MAY 28 2016

.UPDATE...
851 PM CDT

Scattered showers and thunderstorms continue to lift north across
portions of northeast and east central Illinois...and northwest
Indiana this evening. Only anticipate an occasional rumble of
thunder as the showers have been mainly lightning free through
much of the evening...though have slightly intensified over the
Chicago metro area this past hour. Outflow associated with the
showers will also result in a period of stronger southerly winds
gusting 30 to 40 mph. No significant changes were made to the
going forecast.

BMD

&&

.SHORT TERM...
300 PM CDT

Through Tonight...

MCV from earlier morning activity in central and southern Illinois
is moving northeast through the area this afternoon. This activity
is moving into a weakly unstable environment, but is struggling to
grow into deeper convection given this weaker instability, deep
layer shear under 30 kt, and mid level lapse rates that are poor
as well. Expect shower coverage to hold at its current levels or
increase some in the coming hours, with some isolated to scattered
thunder activity as well. The severe threat today is low and
reflected in the marginal risk for severe storms focused farther
west. The concern for scattered storms this afternoon/evening will
be localized heavy downpours in the moisture laden and weak storm
motion environment...along with some gusty winds to 40 mph.
Slightly better instability is found in east central Illinois and
northwest Indiana.

There is another wave moving through the bootheel of Missouri and
southern Illinois that will rotate northeastward tonight ahead of
the negatively tilted trough in the plains, that will keep the
chance for showers and isolated thunderstorms through the evening
and we may see another uptick in activity during this time, but
likely less so overnight as the wave appears to weaken some and
the focus shifts towards the stronger forcing associated with the
upper trough itself. Confidence on coverage during this time is
medium.

KMD

&&

.LONG TERM...
300 PM CDT

Tomorrow through Friday...

The pattern remains active through late next week. Confidence in day
to day convection is not overly high because forcing is weak in most
cases. The atmosphere looks relatively primed for convection,
especially in the near term, but have less confidence in forcing.
Confidence decreases rapidly Thursday night through next Friday due
to model differences.  Highs will remain in the 80s through most of
next week. Lake breezes are possible next week leading to highs in
the upper 60s along the lake.

Saturday is looking very similar to today as far as precip is
concerned. A weak vort streamer lifts north through the day and
expecting convection to increase in coverage to scattered in the
afternoon. Kept PoPs in the generic chance range since the pop up
convection will be hard to catch deterministically in the grids.
Main threat will be heavy rain and perhaps a few will produce gusty
winds. CAPE values look to be less than 1000 J/kg with weak shear.
Pwat values remain high though around 1.75 inches. Storm motion
looks a little better with southwest to northeast movement at around
30-40 kt.

Convection dies off diurnally Saturday night...but left over
convection from the west shifts east through the night. Expecting
the storms to diminish as they do so. Could see some gusty winds as
the storms first breach the western CWA, as depicted by SPC`s day 2
marginal risk.  Areas along and west of I-39 are included in the
marginal risk.

Guidance differs more than I would like with the main upper level
trough Sunday. The GFS is further south than the other models and
thinking precip will be closely tied to the trough. The better storm
coverage will be over Wisconsin...but storms are possible mainly
north and along I-88. Kept a slight chance along and north of I-80
in case the GFS is right. Lifted Pops even further north Sunday
afternoon as the trough lifts northeast with a slight chance along
the IL/WI state line and east of I-55.  CAPE values are forecast to
be below 1000 J/kg again with even weaker shear so not expecting any
severe storms.  Forecast Pwat values are around an inch...but
thinking storms still may produce heavy rain.

We get a break in convection Sunday night through Monday morning!
The GFS and ECMWF bring convection associated with a shortwave into
north central IL Monday afternoon. Have medium-low confidence in the
convection making it into the CWA so capped PoPs in the low chance
range. The GFS is more aggressive than the ECMWF so also limited how
far east the precip gets.  Monday should be mainly dry for most if
not all locations.

Tuesday may be dry, but the GFS features some upper level vort
streamers that may help convection get going. Kept a chance of
thunderstorms in the forecast but have low confidence in PoPs
through the afternoon. Guidance is consistent with additional
convection proceeding an approaching cold front passing through
Wednesday night and Thursday. The GFS is still the most aggressive
with the precip since it has a stronger second upper level low
pressure trough over the plains.  Have low confidence in PoPs
Thursday night into Friday given the drastic differences in
guidance`s upper level patterns. The GFS has a cutoff low over
Kansas while the ECMWF has a closed low over Ontario and a trough
axis moving through the region late it in the week.  Moral of the
story is the pattern remains busy but exact details mid to late next
week are very fuzzy.  Temps in the 80s look solid...with a psbl cool
down into the 70s late next week.

JEE

&&

.AVIATION...
For the 06Z TAFs...

The main concern through the TAF period is with timing the
potential for thunderstorms.

Deep south-southwest flow will persist across the area through
Saturday evening...with warm...moist air mass remaining in place
across the terminals. Forecast soundings indicate this air mass
will become conditionally unstable by this afternoon...with a low
potential for isolated shra/tsra hard to rule out at any particular
time given the potential for subtle minor amplitude mid-level
disturbances to ripple northward ahead of a deeper upper trough
over the central Plains. It appears that Saturday evening will see
the greatest potential for more organized shra/tsra however...as a
stronger mid-level disturbance wraps around the base of the trough
to the west of the area and rotates northeastward into the upper
Midwest. With late afternoon and early evening peak in diurnal
instability and aforementioned forcing aloft...model guidance has
been relatively consistent in depicting thunderstorm development
to the west of the terminals across eastern IA..southwest WI and
western IL. KRFD...in closer proximity to convective development
late in the afternoon likely has a bit higher threat of tsra by
early evening. Threat for Chicago area terminals appears to be
more mid-late evening with model guidance indicating an decaying
line of tsra approaching by 03-04z. While signal for decaying
convection farther to the east is consistent with several models
and over successive runs...forecast soundings indicate sufficient
instability for tsra to continue to move east into Chicago area
should an organized outflow or MCV provide forcing for continued
eastward development. Brief MVFR cig/vis conditions would be
likely with thunderstorms.

Otherwise...south winds will likely gust 20-25 kts later this
morning through this afternoon.

Ratzer

&&

.MARINE...
214 AM CDT

Relatively quiet period for marine weather...with the only issues
being some lingering dense fog over northern parts of the lake and
breezy south winds today and tonight. No recent visibility
observations...though model forecasts indicate fog should become
less widespread with time this morning/today. Will maintain
current dense fog advisory into this afternoon... though would
expect it could be cancelled earlier.

A diffuse area of low pressure was over the central Plains early
this morning...with a warm front arcing across the upper Midwest
and about two thirds of the way up the lake. This low will lift
slowly to the northeast over the weekend...reaching the upper
Mississippi Valley by this evening and moving across far western
Lake Superior by early Sunday. As the low...and the warm front...
move north...winds will shift to the south across the lake. Winds
will gust into the 20-25 kt range today...and 15-20 kt later
tonight and Sunday. Winds across WI and IL will shift west-
southwest behind a cold front on Sunday with gusts 20-25 kt also
affecting the immediate western shore of the lake. Cool water and
warm air will make for a stable marine boundary layer over the
open waters resulting in lighter winds away from shore especially
on the southern part of the lake. The low will continue to pull
slowly away to the northeast of the Great Lakes early next week
with a weaker surface pressure gradient across the lakes bringing
lighter winds. Another low may lift across the upper Midwest mid-
week...with another frontal passage Wednesday or Wednesday night.

Ratzer

&&

.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/NWSCHICAGO
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 272337
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
637 PM CDT FRI MAY 27 2016

.SHORT TERM...
300 PM CDT

Through Tonight...

MCV from earlier morning activity in central and southern Illinois
is moving northeast through the area this afternoon. This activity
is moving into a weakly unstable environment, but is struggling to
grow into deeper convection given this weaker instability, deep
layer shear under 30 kt, and mid level lapse rates that are poor
as well. Expect shower coverage to hold at its current levels or
increase some in the coming hours, with some isolated to scattered
thunder activity as well. The severe threat today is low and
reflected in the marginal risk for severe storms focused farther
west. The concern for scattered storms this afternoon/evening will
be localized heavy downpours in the moisture laden and weak storm
motion environment...along with some gusty winds to 40 mph.
Slightly better instability is found in east central Illinois and
northwest Indiana.

There is another wave moving through the bootheel of Missouri and
southern Illinois that will rotate northeastward tonight ahead of
the negatively tilted trough in the plains, that will keep the
chance for showers and isolated thunderstorms through the evening
and we may see another uptick in activity during this time, but
likely less so overnight as the wave appears to weaken some and
the focus shifts towards the stronger forcing associated with the
upper trough itself. Confidence on coverage during this time is
medium.

KMD

&&

.LONG TERM...
300 PM CDT

Tomorrow through Friday...

The pattern remains active through late next week. Confidence in day
to day convection is not overly high because forcing is weak in most
cases. The atmosphere looks relatively primed for convection,
especially in the near term, but have less confidence in forcing.
Confidence decreases rapidly Thursday night through next Friday due
to model differences.  Highs will remain in the 80s through most of
next week. Lake breezes are possible next week leading to highs in
the upper 60s along the lake.

Saturday is looking very similar to today as far as precip is
concerned. A weak vort streamer lifts north through the day and
expecting convection to increase in coverage to scattered in the
afternoon. Kept PoPs in the generic chance range since the pop up
convection will be hard to catch deterministically in the grids.
Main threat will be heavy rain and perhaps a few will produce gusty
winds. CAPE values look to be less than 1000 J/kg with weak shear.
Pwat values remain high though around 1.75 inches. Storm motion
looks a little better with southwest to northeast movement at around
30-40 kt.

Convection dies off diurnally Saturday night...but left over
convection from the west shifts east through the night. Expecting
the storms to diminish as they do so. Could see some gusty winds as
the storms first breach the western CWA, as depicted by SPC`s day 2
marginal risk.  Areas along and west of I-39 are included in the
marginal risk.

Guidance differs more than I would like with the main upper level
trough Sunday. The GFS is further south than the other models and
thinking precip will be closely tied to the trough. The better storm
coverage will be over Wisconsin...but storms are possible mainly
north and along I-88. Kept a slight chance along and north of I-80
in case the GFS is right. Lifted Pops even further north Sunday
afternoon as the trough lifts northeast with a slight chance along
the IL/WI state line and east of I-55.  CAPE values are forecast to
be below 1000 J/kg again with even weaker shear so not expecting any
severe storms.  Forecast Pwat values are around an inch...but
thinking storms still may produce heavy rain.

We get a break in convection Sunday night through Monday morning!
The GFS and ECMWF bring convection associated with a shortwave into
north central IL Monday afternoon. Have medium-low confidence in the
convection making it into the CWA so capped PoPs in the low chance
range. The GFS is more aggressive than the ECMWF so also limited how
far east the precip gets.  Monday should be mainly dry for most if
not all locations.

Tuesday may be dry, but the GFS features some upper level vort
streamers that may help convection get going. Kept a chance of
thunderstorms in the forecast but have low confidence in PoPs
through the afternoon. Guidance is consistent with additional
convection proceeding an approaching cold front passing through
Wednesday night and Thursday. The GFS is still the most aggressive
with the precip since it has a stronger second upper level low
pressure trough over the plains.  Have low confidence in PoPs
Thursday night into Friday given the drastic differences in
guidance`s upper level patterns. The GFS has a cutoff low over
Kansas while the ECMWF has a closed low over Ontario and a trough
axis moving through the region late it in the week.  Moral of the
story is the pattern remains busy but exact details mid to late next
week are very fuzzy.  Temps in the 80s look solid...with a psbl cool
down into the 70s late next week.

JEE

&&

.AVIATION...
For the 00Z TAFs...

Unsettled weather expected to continue through the TAF cycle.
Isold SHRA could continue to pop up early this evening, but more
organized area of SHRA/Isold TSRA over central IL should lift
north and affect the terminals mid-late this evening. TS will
probably dissipate before this convection arrives. While
additional SHRA cannot be ruled out overnight through Sunday
morning, chances appear low with dry conditions probable. Some
potential exists for sct`d SHRA/TSRA Sunday afternoon and evening
but confidence is low, so kept TAFs dry for now.

Izzi

&&

.MARINE...
304 PM CDT

We have expanded the dense fog advisory for the northern two
thirds of the lake into Saturday as warm moist air runs over the
colder lake. It is not until midday before guidance begins to
erode the fog over the lake. Have kept a single advisory through
mid afternoon for the area for now, though it could erode a bit
sooner in the south and make take a bit longer for the north
portion of the lake. Otherwise, expect some showers and
thunderstorms through this evening, with lower coverage in the
coming days.

Otherwise low pressure will continue to slowly move toward Lake
Superior through the weekend before a weak cold front shifts winds
to light northerly with high pressure.

KMD

&&

.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:
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 270659
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
159 AM CDT FRI MAY 27 2016

.SHORT TERM...
212 PM CDT

Through Friday...

Showers and thunderstorms from this morning have moved East...with
diffluent atmosphere left in the wake this afternoon with becoming
mostly sunny skies. Clouds have been slow to erode...but expect by
late afternoon mainly just a lingering thin cirrus shield
overhead. Upstream across Northern Missouri an area of
thunderstorms was developing...however guidance does not indicate
that this will lift towards Northern Illinois this evening. Have
trended towards a dry late afternoon persisting...and likely into
the evening hours as well. Some of the hi-res forecast guidance
continues to indicate a few showers/thunderstorms developing as a
weak lobe of vorticity lifts North after 4z...however with 500mb
heights likely to hold through this evening the potential for any
organized convection looks very low through at least 6z...then
have trimmed back on pops through the remainder of the overnight
with just a slight chance increasing towards chance by daybreak.

Winds should diminish with the lack of a gradient in the near
surface environment later this evening as well...and with dew
points in the middle 60s progged to advect North/Northeast pushing
PWAT values towards 1.5 to 2 inches...it is conceivable that some
patchy fog may develop. At this time have held it out of the
current forecast as there may be just enough wind at 1000-1500ft
to keep some mixing. With the high water content in the lowest
layers of the atmosphere...temps will be slow to cool tonight and
likely remain mild. Have adjusted temps to the mid/upr 60s...but
could easily see temps not dropping below 70 closer to downtown
Chicago and perhaps a few other locations. Cloud cover tonight
will also play a role in lows.

For Friday a deep trough remains anchored across the Central
Plains with the continued Southwest to Northeast feed of moisture
towards the Western Great Lakes/Ohio Valley. There is a weakly
defined surface low that will remain near the upper level
trough...but a weak mid-lvl vort wave will lift Northeast across
the forecast area later Friday morning through the afternoon. At
this time not anticipating any severe storms for Friday with the
continued lack of shear in the lowest 0-3km along with weak
forcing...but if any storms develop Fri aftn the greater concern
will be on brief heavy downpours given the anomalous PWAT that is
progged for the area.

With anticipated considerable cloud cover for Fri...temps will
likely hold in the lower 80s with some locations nearing the mid
80s mainly in the Southeast CWFA.

Beachler

&&

.LONG TERM...
257 PM CDT

Friday night through Thursday...

The extended continues to look busy with a chance of thunderstorms
every day.  High temperatures will be in the 80s each day...but lake
side cooling develops next week.  Could see even warmer high temps
if we get more sun than forecast.

For thunderstorms...forcing will be the big question each day.
Thinking we will have leftover convection spread along and west of I-
55 Friday night and then dissipate Saturday morning.  A weak vort
streamer swings through the region Saturday while the main short
wave stays well west of the region over SD and NE.  Cannot rule out
a few thunderstorms so kept a chance of thunderstorms going in the
forecast.  Forecasted CAPE looks skinny and we are also lacking
shear. A few storms may become strong...but not expecting any severe
storms.  Pwat values will still be around 1.5 inches and storm
motion will be around 20-30 kt.  Storms will be probably produce
heavy rain but should be moving quick enough to avoid flooding.
However...a few training storms could produce localized flooding
like we saw yesterday.

The story looks similar for next week with no clear forcing but
ample CAPE and moisture.  Lingering convection weakens as it spreads
over the region Saturday night and once again expecting better
thunderstorm coverage along and west of I-55.  The big questions
Sunday will be how quickly we recover from the morning convection
and how much forcing we will get from the shortwave/vort streamer
that rotates through. Forecast soundings feature a decent cap and
little to no shear again.  If we recover...could see better
thunderstorm coverage than what is currently forecast.  Still only
expecting a few stronger storms due to the lack of shear.  Thinking
there will be better thunderstorm coverage over WI closer to the
shortwave.

Thinking Monday will be dry so backed off on precip chances. A
better chance of thunderstorms arrives ahead of a cold front Tuesday
and more likely Tuesday evening/night. Long range guidance does
differ with the exact path of the low next week so have low
confidence in timing and details of storms from Tuesday onward.

JEE

&&

.AVIATION...
For the 06Z TAFs...

The main forecast concern will be with the potential and timing
of any thunderstorms over the area today.

An atmospheric disturbance is currently driving a cluster of showers
and storms to our southwest over northeastern MO and into portions
of west central IL. This activity is expected to shift to the
northeast through the night...but will likely do so in a weakening
fashion. Remnants of this activity could move over the terminals
after daybreak today...but at this time...I only prefer to mention a
VCSH.

The convective picture looks a bit murky through this afternoon and
evening. The only real feature of interest...which could drive a
period of thunderstorms over the area later this afternoon...is an
upper level disturbance currently noted over the ARKLATEX region.
Forecast guidance suggests this disturbance will shift
northeastward over northeastern IL later in the day during peak
heating. As such...this could be enough to result in thunderstorm
development over the area after 20Z this afternoon. Overall
confidence is low to medium at best at this juncture. However...I
felt justified to include a PROB30 mention for thunder at the
terminals.

KJB

&&

.MARINE...
159 AM CDT

The main weather concerns over Lake Michigan will be the continued
dense fog today...especially over the northern half of the
lake...and also the potential for more thunderstorms.

Light winds and high a dew point air mass over Lake Michigan is
resulting in dense fog...especially over the northern half of the
lake. It appears that this fog will persist through the day
today...and possibly well into tonight as well. As a result...we
have extended the dense fog advisory through late tonight for the
north end of the lake. It appears that although some fog could
persist over the south end of the lake...that the fog advisory there
may be allowed to expire later this morning.

An area of low pressure over the plains...is expected to shift
northeastward over the upper Midwest late Saturday. This storm
system will result in the possibility of a few waves of showers and
storms over the next couple of days. Additionally...it appears that
south winds will be on the increase into the 15 to 20 KT range for
Saturday and Sunday as the low lifts into Ontario.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Dense Fog Advisory...LMZ777-LMZ779 UNTIL 9 AM Friday.

&&

$$

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000
FXUS63 KLOT 261140
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
640 AM CDT THU MAY 26 2016

.SHORT TERM...
328 AM CDT

Through Tonight...

Concerns for today and tonight are once again on thunderstorm
timing and coverage with a more unstable and moist air mass than
yesterday...however less of a forcing mechanism. Have boosted
high temperatures with fairly widespread upper 80s forecast.

Another morning with a couple MCSs to the west over IA and
northern MO. A low amplitude short wave trough has been helping
to sustain these on the nose of a 40 kt low-level jet /LLJ/ and
this feature will continue east-northeast. Recent IR trends have
indicated sustained cloud top temperatures...so expecting at least
a broken line of showers and probably some storms making it into
north central Illinois around 8 a.m. or so. These should be in a
fading state with the LLJ gradually weakening. These very well
could completely fade by Chicago/northwest Indiana later this
morning as they outrun their environmental support.

Convective debris clouds this morning...especially over parts of
northern Illinois...may initially slow the rate of warming. But
the past two days any clouds have done little to prevent readings
from reaching several degrees above guidance. The 925mb
temperatures observed last eve on soundings were 22C-23C. In late
May over the past 30 years readings of 22C or warmer correlate to
a mean high of 88 at Chicago ORD. So feel comfortable with the
upper 80s in most areas with dew points inching into the upper
60s. This will certainly give a muggy feel with apparent
temperatures in the lower 90s.

The high theta-e air warm sector spreading over the region this
afternoon will support large amounts of instability characterized
by MLCAPES in excess of 2500 J/KG...assuming T/Td forecasts are
on track. A cap...albeit weak...is expected to be in place along
with limited low-level convergence/focus or a forcing mechanism.
The exception to this may be if there is any lingering weak
forcing or elevated boundary from the morning activity...which
probably would be over the southeast forecast area this afternoon.
The experimental HRRR and a couple other convective allowing
models try to indicate some afternoon development there. In this
high CAPE/PWAT air mass feel comfortable keeping a chance for
isolated storms areawide this afternoon into the evening. Any
that do trigger will need to be monitored for brief large hail
and downbursts...but again that is a conditional threat.

In response to the upper low ejecting from the Four Corners
region tonight...strong moisture transport in the low to mid
levels will likely foster convection across IA and potentially
western IL this evening. Convection should want to grow northeast
within improving upper diffluence and some scattered mainly
elevated storms may develop into the northern IL portion of the
CWA. Confidence on this is low at this time and may depend on just
how much is developing in the Ozarks/MO that could rob our
moisture replenishment this way. Severe potential with any of
these late night storms is also marginal...and would be mainly
brief hail.

MTF

&&

.LONG TERM...
345 AM CDT

Friday through Wednesday...

The ejecting upper low as mentioned above will shift a high PWAT
air mass /AOA 1.5 inches/ over the Mississippi River valley by
midday Friday. The challenge is how quickly and how much rain will
spread east as similar upper lows over the past few weeks have
struggled to expand rain into the area within a similar semi-
blocked pattern. The difference with this is a wide open Gulf of
Mexico with a strong fetch of moisture transport. Almost all
guidance provides the western CWA with more rainfall on
Friday/Friday Night than the east and have tightened the gradient
on PoPs and rainfall amounts but feel it will probably need to be
done more so during the day Friday and possibly Friday evening.
Still expect eastern areas to get showers...just not sure how
quickly and it may not be until Friday night or even Saturday
morning. The synoptic setup gets less favorable for severe weather
and more so for heavy rainfall with PWATs approaching the 99th
percentile. The model ensemble spread for rainfall is quite large
over the area...with higher members in the two to three inch
range...so will need to monitor hydrology concerns...especially
with some localized amounts over 1.50 inches last night. The
chances for rain and some storms will continue into
Saturday...with more of an unstable air mass trying to push back
into the area...although forcing could be diminishing.

Upper ridging atop a weak surface high is expected to set up by
Sunday. As this draws near and our confidence has increased...we
are able to keep more of the area dry in the forecast for Sunday
and Memorial Day. Highs are forecast in the lower to mid 80s.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

640 am...Broken line of thunderstorms extends from southwest WI
through the Quad Cities with more widespread thunderstorms across
central IL. Short term/Hi res guidance has been showing this
activity weakening as it moves east across north central IL over
the next few hours. However...this trend has not yet emerged and
some of the activity near the Quad Cities has strengthened. With
uncertainty regarding how long this activity will persist before
weakening...opted to include a short tempo for thunder at all the
terminals this morning. Wind shift across far northeast IA and
southern WI will likely make it into rfd with a period of stronger
westerly winds.

Low confidence regarding thunderstorm chances after this morning.
Convection over the central plains later today and this evening
will likely move east tonight and possibly into northwest or
northern IL overnight or toward daybreak Friday. Despite the low
confidence opted to include prob mention at rfd toward sunrise
Friday morning.

South/southwest winds around 10kt will likely increase into the
12-15kt range this afternoon as skies are expected to clear and
low levels mix. Its possible wind speeds may be a bit higher and
gusts into the mid/upper teen range will be possible. Winds will
settle back to light southerly this evening. Some light fog will
also be possible tonight especially if skies are generally clear.
cms

&&

.MARINE...

142 am...A warm front will continue lifting north across northern
portions of Lake Michigan this morning shifting winds southerly. A
large trough of low pressure is expected to remain across the
plains into Saturday maintaining moist southerly flow across the
lake. This will lead to continued fog development and likely dense
fog today through Friday and a dense fog advisory may be needed.

A weak cold front is expected to move across the lake Saturday
night shifting winds westerly with weak high pressure settling
over the lakes region early next week resulting in winds turning
northeast Monday night or Tuesday. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...Dense Fog Advisory...LMZ777-LMZ779 UNTIL 9 AM Friday.

&&

$$

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000
FXUS63 KLOT 260315
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1015 PM CDT WED MAY 25 2016

.UPDATE...
1005 PM CDT

Lingering convection late this evening will continue to wane and
should be done over the next couple hours with primarily dry
conditions expected across the CWA after midnight. Lowered PoPs
for the overnight hours as the threat for nocturnal convection
associated with the LLJ appears less favorable across northern
Illinois than previously expected. Strong convection is occurring
across NE KS late this evening and expect coverage to increase as
a modest LLJ strengthens across the Missouri Valley. Best
moisture convergence should be in place across southern IA into
northern MO with convection spreading eastward as the LLJ veers
overnight. RAP/NAM indicate that instability will spread back to
the NE overnight however the instability gradient is progged to be
draped from northern MO into central IL. Expect convection to
build SE along the gradient overnight which should keep the local
forecast area dry. Will maintain slight chance PoPs late tonight
into early Thursday but best chances should be to our SW.

Will also have to keep an eye on some patchy fog potential
overnight. Juicy airmass in place with mid 60 dewpoints late this
evening along with recent rainfall and light flow could allow some
reduction in the visibility. We may also see some brief partial
clearing before additional mid/high clouds move in later tonight
that would support some radiational cooling with temp-dewpoints
spreads already only a couple/few degrees for the northern half of
the CWA.

Deubelbeiss

&&

.SHORT TERM...
232 PM CDT

Through Tonight...

No real significant changes with thoughts for thunderstorms this
afternoon into the evening, with scattered development likely
impact much of the area.

Latest radar imagery depicting isolated to widely scattered
storms developing just west of I39, focused along weak convergence
over northwest Indiana. Increasing instability supported by
steepening lapse rates and with diminishing CIN will continue over
the next couple of hours as large scale ascent further increases
with the approach of mid level energy. Most short term guidance
still indicating further expansion of what is occurring at this
time over the next 2-3, while likely shifting east with time and
feel fairly confident with this solution. Also feel fairly
confident with timing, once again, highlighting the 20/22z time
frame over north central Illinois and then the 21/23z period for
northeast Illinois and northwest Indiana for increasing coverage
and intensity of thunderstorm development. This also includes the
possibility for isolated strong to maybe severe storms across the
entire area, with hail/wind still the likely hazards. Overall
development should likely diminish by mid evening, however, some
guidance continues to develop additional thunderstorms beyond this
period likely owing to an increasing LLJ with large scale ascent
still overhead. Do think the guidance that is showing this
development is a bit overdone with coverage at that time, which
could be associated to boundaries that more than likely wont be in
place. Nonetheless, still maintained low chance to slight chance
pops wording overnight, but focus it more south with time as the
focus shifts south tonight.

Rodriguez/Monteleone

&&

.LONG TERM...
239 PM CDT

Thursday night through Wednesday...

Thursday through Saturday...
The pattern continues to be very summer like over the next several
days...heading into the holiday weekend. Deep trough continues to
rotate across the Southwest CONUS Thursday but will begin to drift
East Friday and weaken. However as the trough begins to approach the
Western Great Lakes/Ohio Valley Friday...the added low level
moisture and vorticity throughout the lowest layers of the
atmosphere...and a weak sfc shortwave could translate into increased
chances for precip/thunderstorms heading into Friday. The challenge
for Friday could be that several guidance members indicate some mid-
lvl height rises through the afternoon...which could hold onto the
diffluent flow in the mid-lvls longer and delay precip chances until
late afternoon/evening. Low level moisture will be present
however...with dew points pushing well into the 60s and a few near
70 degree dew points is conceivable as precipitable water values
approach 1.5 inches Friday. So the humidity will be felt throughout
the region Friday with highs warming into the lower to middle 80s
once again.

Saturday could be very similar to Friday...as the overall pattern
remains relatively un-changed. The better precip chances will be
shifting North throughout the day...with temps generally in the
lower 80s. Cloud cover and perhaps some morning convection could
linger and keep a thicker cloud shield in place which may hold temps
down a few degrees.

Sunday through middle of next week... For the second half of the
holiday weekend through the middle of next week the pattern
continues to feature weak ridging across the Great Lakes region.
There is some weakening in the longwave pattern...however the spread
amongst ensemble members in the longer term does not grow much. Thus
the confidence does remain higher that the continued warm/humid
pattern will likely persist with occasional showers/thunderstorms
throughout the extended periods.

Beachler

&&

.AVIATION...
FOR THE 00Z TAFS...

Main concern is with thunderstorm and wind trends this evening.
An upper level disturbance kicked off areas of TSRA late this
afternoon, with associated stronger winds in the first wave.
Concern has diminished for strong to severe gusts at the
terminals. However, until the disturbance departs to the east
later this evening, expecting TSRA to hang around the northeast IL
terminals, with occasional IFR to LIFR vsby in heavy rain and
ocnl cloud to ground lightning. Pushed back end time to 03z. The
wind field is disturbed by the thunderstorms and various outflow
boundaries generated by them. Confidence is low with trends.
Including temporary east winds in the ORD TAF and started MDW with
current north winds, with the potential for a temporary shift to
east winds.

After the thunderstorms this evening, cannot completely rule out
isolated SHRA or TSRA overnight, but there is no good source of
lift noted on satellite imagery. Next disturbance is expected to
move across the area toward daybreak. Confidence is low with
trends with this wave overall. Per timing of disturbance and model
guidance, pushed back timing of PROB30 for TSRA. After any
potential TSRA ends by mid morning, atmosphere will become
unstable, so isolated SHRA/TSRA are possible. However, confidence
is low and it appears more favored timing will be associated with
a stronger disturbance moving in beyond the ORD 30-hour TAF. Kept
all TAFs dry after the morning PROB30 given the low confidence.
Winds will be south-southwest on Thursday with gusts of 15-20 kt
and otherwise VFR conditions.

RC

&&

.MARINE...
306 PM CDT

Have continued the dense fog advisory for the Northern half of
Lake Michigan through this evening. With increasing low level
moisture flowing North/Northeast over the lake...dense fog will
likely persist and could result in the advisory needing to be
extended. Winds will continue to be Southerly with speeds between
10 to 20 kts...then slowly diminish overnight to around 10 to 15
kts. A frontal boundary has become stationary over the Southern
half of the lake...but will lift back North Thursday with another
frontal boundary remaining well West of the Great Lakes through
the next few days. A large area of low pressure will remain
positioned West of the lakes with continued warm Southerly flow
and the potential for areas of fog through Friday and perhaps
Saturday.

Beachler

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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000
FXUS63 KLOT 260111
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
811 PM CDT WED MAY 25 2016

.SHORT TERM...
232 PM CDT

Through Tonight...

No real significant changes with thoughts for thunderstorms this
afternoon into the evening, with scattered development likely
impact much of the area.

Latest radar imagery depicting isolated to widely scattered
storms developing just west of I39, focused along weak convergence
over northwest Indiana. Increasing instability supported by
steepening lapse rates and with diminishing CIN will continue over
the next couple of hours as large scale ascent further increases
with the approach of mid level energy. Most short term guidance
still indicating further expansion of what is occurring at this
time over the next 2-3, while likely shifting east with time and
feel fairly confident with this solution. Also feel fairly
confident with timing, once again, highlighting the 20/22z time
frame over north central Illinois and then the 21/23z period for
northeast Illinois and northwest Indiana for increasing coverage
and intensity of thunderstorm development. This also includes the
possibility for isolated strong to maybe severe storms across the
entire area, with hail/wind still the likely hazards. Overall
development should likely diminish by mid evening, however, some
guidance continues to develop additional thunderstorms beyond this
period likely owing to an increasing LLJ with large scale ascent
still overhead. Do think the guidance that is showing this
development is a bit overdone with coverage at that time, which
could be associated to boundaries that more than likely wont be in
place. Nonetheless, still maintained low chance to slight chance
pops wording overnight, but focus it more south with time as the
focus shifts south tonight.

Rodriguez/Monteleone

&&

.LONG TERM...
239 PM CDT

Thursday night through Wednesday...

Thursday through Saturday...
The pattern continues to be very summer like over the next several
days...heading into the holiday weekend. Deep trough continues to
rotate across the Southwest CONUS Thursday but will begin to drift
East Friday and weaken. However as the trough begins to approach the
Western Great Lakes/Ohio Valley Friday...the added low level
moisture and vorticity throughout the lowest layers of the
atmosphere...and a weak sfc shortwave could translate into increased
chances for precip/thunderstorms heading into Friday. The challenge
for Friday could be that several guidance members indicate some mid-
lvl height rises through the afternoon...which could hold onto the
diffluent flow in the mid-lvls longer and delay precip chances until
late afternoon/evening. Low level moisture will be present
however...with dew points pushing well into the 60s and a few near
70 degree dew points is conceivable as precipitable water values
approach 1.5 inches Friday. So the humidity will be felt throughout
the region Friday with highs warming into the lower to middle 80s
once again.

Saturday could be very similar to Friday...as the overall pattern
remains relatively un-changed. The better precip chances will be
shifting North throughout the day...with temps generally in the
lower 80s. Cloud cover and perhaps some morning convection could
linger and keep a thicker cloud shield in place which may hold temps
down a few degrees.

Sunday through middle of next week... For the second half of the
holiday weekend through the middle of next week the pattern
continues to feature weak ridging across the Great Lakes region.
There is some weakening in the longwave pattern...however the spread
amongst ensemble members in the longer term does not grow much. Thus
the confidence does remain higher that the continued warm/humid
pattern will likely persist with occasional showers/thunderstorms
throughout the extended periods.

Beachler

&&

.AVIATION...
FOR THE 00Z TAFS...

Main concern is with thunderstorm and wind trends this evening.
An upper level disturbance kicked off areas of TSRA late this
afternoon, with associated stronger winds in the first wave.
Concern has diminished for strong to severe gusts at the
terminals. However, until the disturbance departs to the east
later this evening, expecting TSRA to hang around the northeast IL
terminals, with occasional IFR to LIFR vsby in heavy rain and
ocnl cloud to ground lightning. Pushed back end time to 03z. The
wind field is disturbed by the thunderstorms and various outflow
boundaries generated by them. Confidence is low with trends.
Including temporary east winds in the ORD TAF and started MDW with
current north winds, with the potential for a temporary shift to
east winds.

After the thunderstorms this evening, cannot completely rule out
isolated SHRA or TSRA overnight, but there is no good source of
lift noted on satellite imagery. Next disturbance is expected to
move across the area toward daybreak. Confidence is low with
trends with this wave overall. Per timing of disturbance and model
guidance, pushed back timing of PROB30 for TSRA. After any
potential TSRA ends by mid morning, atmosphere will become
unstable, so isolated SHRA/TSRA are possible. However, confidence
is low and it appears more favored timing will be associated with
a stronger disturbance moving in beyond the ORD 30-hour TAF. Kept
all TAFs dry after the morning PROB30 given the low confidence.
Winds will be south-southwest on Thursday with gusts of 15-20 kt
and otherwise VFR conditions.

RC

&&

.MARINE...
306 PM CDT

Have continued the dense fog advisory for the Northern half of
Lake Michigan through this evening. With increasing low level
moisture flowing North/Northeast over the lake...dense fog will
likely persist and could result in the advisory needing to be
extended. Winds will continue to be Southerly with speeds between
10 to 20 kts...then slowly diminish overnight to around 10 to 15
kts. A frontal boundary has become stationary over the Southern
half of the lake...but will lift back North Thursday with another
frontal boundary remaining well West of the Great Lakes through
the next few days. A large area of low pressure will remain
positioned West of the lakes with continued warm Southerly flow
and the potential for areas of fog through Friday and perhaps
Saturday.

Beachler

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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