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000
FXUS63 KLOT 232207
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
507 PM CDT WED APR 23 2014

.DISCUSSION...
310 PM CDT

SYNOPSIS...ANOTHER PLEASANT DAY TODAY...BUT SHOWERS MOVE IN FROM THE
WEST THIS EVENING. SHOWERS AND STORMS ARE EXPECTED TOMORROW
AFTERNOON AND EVENING WITH A DRY AND WARM END TO THE WORK WEEK.
THIS WEEKEND LOOKS TO HAVE BELOW NORMAL TEMPERATURES WITH SHOWERS
AND PERHAPS SOME THUNDERSTORMS ALONG AND SOUTH OF I-80 FOR THE FIRST
HALF OF NEXT WEEK.

REST OF TODAY AND TONIGHT...
A LARGE UPPER LEVEL RIDGE IS OVER THE CENTRAL PLAINS WHILE A SURFACE
HIGH IS CENTERED OVER LAKE MICHIGAN. THE RIDGE PASSES OVERHEAD
TONIGHT WHILE THE SURFACE HIGH PUSHES EAST TO THE NORTHERN OHIO
VALLEY THROUGH EASTERN QUEBEC.

A WEAK SHORTWAVE IS OVER EASTERN NEBRASKA AND WESTERN IOWA WITH
SHOWERS OVER WESTERN IOWA.  THE SHOWERS WILL CONTINUE TO PUSH
EAST...BUT WITH DEWPOINT DEPRESSIONS AT 20+ DEGREES...THINKING THE
SHOWERS WILL DISSIPATE A BIT BEFORE MOVING INTO CENTRAL IL. AS SUCH
THINKING THE FIRST SHOWERS WILL ENTER THE FAR EASTERN CWA AFTER 5PM
CST.  USED THE LOCAL ARW...RAP...AND HRRR TO CREATE THE POPS FOR THE
REST OF TODAY AND TONIGHT. THINKING A BAND OF SCATTERED SHOWERS WILL
SLOWLY CROSS NORTHERN IL THIS EVENING IN ASSOCIATION WITH AN UPPER
LEVEL VORTICITY STREAMER. THE BEST COVERAGE WILL BE BETWEEN MIDNIGHT
AND 4 AM CST WITH A CHANCE OF LIGHT RAIN SHOWERS NORTH OF I-80. THE
BAND THEN LIFTS NORTH EARLY THURSDAY MORNING AS THE RIDGE MOVES
DIRECTLY OVERHEAD. NOT EXPECTING ANY SIGNIFICANT PRECIP
ACCUMULATIONS.

CLOUD COVER WILL INCREASE THROUGH THIS AFTERNOON AND LOOKING AT MIN
TEMPS IN THE UPPER 30S TO MID 40S ACROSS THE CWA.

TOMORROW AND TOMORROW NIGHT...
AN UPPER LEVEL TROUGH MOVES OVER THE PLAINS TOMORROW MORNING AND THE
TROUGH PASSES OVER THE REGION TOMORROW NIGHT. THE UPPER LEVEL LOW
ASSOCIATED WITH THE TROUGH PASSES FARTHER NORTH...ALONG THE
US/CANADA BORDER.  THE SURFACE LOW ALSO BEGINS OVER THE PLAINS
THURSDAY MORNING AND THEN MOVES OVER IL THURSDAY EVENING. GUIDANCE
HAS THE LOW PROGRESSING A BIT SLOWER AND MADE THE NECESSARY
ADJUSTMENTS.

RAIN AND SOME STORMS MOVE IN FROM THE WEST THROUGH THE MORNING AND
EARLY AFTERNOON.  INSTABILITY IS NOT EXTREMELY IMPRESSIVE WITH THE
SYSTEM SO KEPT ONLY A CHANCE OF THUNDER. QPF AMOUNTS ON THE OTHER
HAND COULD BE IMPRESSIVE WITH TOTALS AROUND A HALF INCH OF RAIN.

WINDS WILL ALSO BE SHIFTING FROM SOUTHEAST IN THE MORNING TO OUT OF
THE WEST OVERNIGHT BEHIND THE LOW.  LOOKING AT A BREEZY AFTERNOON
WITH SOUTH WINDS GUSTING TO 35 MPH.  THE AMPLE WAA WILL LEAD TO MAX
TEMPS FROM AROUND 60 ALONG THE IL/WI BORDER TO THE UPPER 60S IF NOT
70 IN THE SOUTHERN CWA.

FRIDAY AND SATURDAY...
THE UPPER LEVEL LOW CONTINUES TO SHIFT EAST REACHING NEW ENGLAND BY
SATURDAY AFTERNOON/EVENING.  THE SURFACE LOW SHIFTS EAST AND
EXPECTING PRECIP TO COME TO AN END EARLY FRIDAY MORNING.  WEST WINDS
WILL BE GUSTING TO ARND 30 MPH FRIDAY AND AM THINKING THERE COULD BE
SOME DRY AIR MIXING DOWN TO THE SURFACE SO LOWERED DEWPOINTS A BIT.

THE AIR BEHIND THE COLD FRONT IS NOT REALLY ALL THAT COLD SINCE MAX
TEMPS ON FRIDAY LOOK TO BE AROUND 70 DEGREES.  A BACK DOOR COLD
FRONT SLIDES DOWN FROM THE NORTH IN THE EVENING. SOME GUIDANCE
MEMBERS FEATURE A BAND OF PRECIP FORMING AHEAD OF THE FRONT OVER FAR
NORTHERN IL AND NW INDIANA. PUT IN A CHANCE OF PRECIP SINCE FORCING
LOOKS GOOD...BUT HAVE LOW CONFIDENCE IN THE BAND OF PRECIP ACTUALLY
FORMING. AS SUCH KEPT POPS IN THE CHANCE RANGE.  WINDS TURN
NORTHEAST BEHIND THE FRONT AND OVERNIGHT LOWS WILL BE IN THE UPPER
30S TO MID 40S.

SOME GUIDANCE MEMBERS KEEP A BAND OF PRECIP OVER THE REGION SATURDAY
MORNING...BUT WITH HIGH PRESSURE MOVING OVER THE REGION HAVE LOW
CONFIDENCE AND WENT WITH A DRY FORECAST SATURDAY.  SKIES WILL CLEAR
BUT THE COOLER AIR OFF THE LAKE WILL RESULT IN HIGHS IN THE UPPER
40S TO MID 50S ALONG THE LAKE...AND THEN IN THE LOW TO MID 60S IN
THE OUTLYING AREAS.

GUIDANCE FEATURES PRECIP MOVING IN AHEAD OF THE NEXT LOW SATURDAY
NIGHT. HAVE LOW CONFIDENCE IN THIS ROUND OF PRECIP AS WELL...BUT
LEFT A CHANCE OF RAIN IN THE FORECAST.  OVERNIGHT LOWS WILL RANGE
FROM THE UPPER 30S TO THE MID 40S.

EXTENDED...SUNDAY THROUGH TUESDAY...
AN UPPER LEVEL CLOSED LOW SHIFTS OVER THE GREAT PLAINS SUNDAY
EVENING/NIGHT. GUIDANCE DIFFERS ON ITS EXACT PATH EARLY NEXT WEEK
BUT DOES HAVE THE UPPER LEVEL LOW OVER THE REGION THROUGH AT LEAST
MID WEEK.  ITS ASSOCIATED SURFACE LOW MOVES OVER THE PLAINS LATE
SUNDAY NIGHT/MONDAY MORNING AND SLIDES SOUTH OF THE CWA MONDAY
NIGHT. THE 12Z GUIDANCE AGREED A BIT MORE ABOUT THE SURFACE LOWS
PATH...AND HAVE IT MOVING THROUGH SOUTHERN IL TUESDAY.

IN TWO WORDS EARLY NEXT WEEK LOOKS CHILLY AND WET.  A BOUNDARY OVER
NORTHERN IL BRINGS THE LIFT FOR THE FIRST WAVE OF PRECIP EARLY ON
SUNDAY...BUT THEN MULTIPLE VORTICITY STREAMERS PASS THROUGH THE
REGION AS THE LOW SLOWLY SHIFTS EAST. THIS WILL RESULT IN A CHANCE
OF PRECIP THROUGHOUT THE EXTENDED. WILL INCLUDE A SLIGHT CHANCE OF
THUNDER ALONG AND SOUTH OF I-80 WHERE THERE WILL BE LIMITED ELEVATED
INSTABILITY BUT ENOUGH TO PERHAPS SUPPORT A COUPLE OF THUNDERSTORMS
SUNDAY NIGHT AND MONDAY. THE UPPER LEVEL JET DIPS FAR SOUTH THROUGH
TEXAS ALLOWING COOL AIR TO SPREAD ACROSS THE REGION. AS SUCH HIGHS
WILL VARY BETWEEN THE LOW 50S NORTH TO MID 60S SOUTH WITH A COOLING
TREND THROUGH TUESDAY.  LUCKILY OVERNIGHT LOWS LOOK LIKE THEY WILL
REMAIN ABOVE FREEZING.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* VARIABILITY IN THE WINDS REST OF THIS AFTERNOON FROM NNE TO ESE.
* CHANCE FOR SHOWERS THIS EVENING...THEN BETTER CHANCES FOR
  SHOWERS LATE THURSDAY AFTERNOON.
* WINDS VEERING TO SSE BY TOMORROW...THEN BECOMING VERY GUSTY LATE
  TOMORROW MORNING INTO THE AFTERNOON.

BMD/CMS

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST AWAY FROM THE
TERMINALS THIS AFTERNOON WITH WINDS CONTINUING TO VEER FROM THE
NORTHEAST EARLY THIS AFTERNOON TO THE SOUTHEAST OVERNIGHT. SHOWERS
CURRENTLY OVER SOUTHERN MINNESOTA AND IOWA MAY SKIRT THE IL/WI STATE
LINE LATE THIS AFTERNOON THROUGH LATE EVENING BRINGING A SMALL CHANCE
FOR SHOWERS. COVERAGE IS STILL UNCERTAIN SO WILL MAINTAIN PROB30 FOR
THE CHICAGO TERMINALS AND VCSH FOR RFD. MEANWHILE...LOW PRESSURE
WILL DEVELOP OVER THE SOUTHERN PLAINS AND LIFT TO THE MID
MISSISSIPPI VALLEY BY MIDDAY THURSDAY. THE GRADIENT WILL TIGHTEN
AHEAD OF THE LOW WITH GUSTS GRADUALLY INCREASING INTO THE UPPER 20
KT RANGE OT OF THE SSE...AND CANNOT RULE OUT SOME GUSTS IN EXCESS OF
30 KT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL THEN OVERSPREAD
THE TERMINALS MID TO LATE THURSDAY AFTERNOON.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION THIS AFTERNOON...MEDIUM-HIGH
  CONFIDENCE ON WIND DIRECTION/SPEED THURSDAY.
* LOW CONFIDENCE IN PRECIP AT TERMINALS THIS EVENING...MEDIUM
  CONFIDENCE IN PRECIP TIMING THURSDAY AFTERNOON.

BMD/CMS

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
219 PM CDT

PROGRESSIVE FLOW WILL CONTINUE THROUGH FRIDAY BEFORE A MUCH MORE
AMPLIFIED AND LOCKED PATTERN WILL SET UP FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK. THE HIGH PRESSURE PRESENTLY OVER THE LAKE WILL
BE SCOOTED EASTWARD EARLY FRIDAY AS LOW PRESSURE FROM THE CENTRAL
PLAINS BOOKS EASTWARD INTO NORTHERN INDIANA. DURING THURSDAY THIS
WILL PROVIDE STRONG SOUTHERLY FLOW. A FAIRLY STOUT INVERSION SHOULD
BE PRESENT OVER THE LAKE...BUT STRONG OFFSHORE WINDS IN NEARSHORE
AREAS SHOULD LEAD TO 25 TO POSSIBLE 30 KT GUSTS. AS A DEEP TROUGH
SETS UP ACROSS THE WESTERN U.S. AND SLOWLY MOVES EAST THROUGH THE
WEEKEND AND EARLY NEXT WEEK...SURFACE HIGH PRESSURE WILL GET
LOCKED OVER THE CENTRAL GREAT LAKES. A TIGHTENING PRESSURE
GRADIENT ON ITS SOUTHERN AND WESTERN SIDES WILL PROVIDE CONTINUOUS
EAST TO NORTHEAST SURFACE WINDS. THIS LOOKS LIKE A POTENTIAL
PROLONGED PERIOD OF SMALL CRAFT ADVISORY CRITERIA.

MTF

&&

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

&&

$$

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 232010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 PM CDT WED APR 23 2014

.DISCUSSION...
310 PM CDT

SYNOPSIS...ANOTHER PLEASANT DAY TODAY...BUT SHOWERS MOVE IN FROM THE
WEST THIS EVENING. SHOWERS AND STORMS ARE EXPECTED TOMORROW
AFTERNOON AND EVENING WITH A DRY AND WARM END TO THE WORK WEEK.
THIS WEEKEND LOOKS TO HAVE BELOW NORMAL TEMPERATURES WITH SHOWERS
AND PERHAPS SOME THUNDERSTORMS ALONG AND SOUTH OF I-80 FOR THE FIRST
HALF OF NEXT WEEK.

REST OF TODAY AND TONIGHT...
A LARGE UPPER LEVEL RIDGE IS OVER THE CENTRAL PLAINS WHILE A SURFACE
HIGH IS CENTERED OVER LAKE MICHIGAN. THE RIDGE PASSES OVERHEAD
TONIGHT WHILE THE SURFACE HIGH PUSHES EAST TO THE NORTHERN OHIO
VALLEY THROUGH EASTERN QUEBEC.

A WEAK SHORTWAVE IS OVER EASTERN NEBRASKA AND WESTERN IOWA WITH
SHOWERS OVER WESTERN IOWA.  THE SHOWERS WILL CONTINUE TO PUSH
EAST...BUT WITH DEWPOINT DEPRESSIONS AT 20+ DEGREES...THINKING THE
SHOWERS WILL DISSIPATE A BIT BEFORE MOVING INTO CENTRAL IL. AS SUCH
THINKING THE FIRST SHOWERS WILL ENTER THE FAR EASTERN CWA AFTER 5PM
CST.  USED THE LOCAL ARW...RAP...AND HRRR TO CREATE THE POPS FOR THE
REST OF TODAY AND TONIGHT. THINKING A BAND OF SCATTERED SHOWERS WILL
SLOWLY CROSS NORTHERN IL THIS EVENING IN ASSOCIATION WITH AN UPPER
LEVEL VORTICITY STREAMER. THE BEST COVERAGE WILL BE BETWEEN MIDNIGHT
AND 4 AM CST WITH A CHANCE OF LIGHT RAIN SHOWERS NORTH OF I-80. THE
BAND THEN LIFTS NORTH EARLY THURSDAY MORNING AS THE RIDGE MOVES
DIRECTLY OVERHEAD. NOT EXPECTING ANY SIGNIFICANT PRECIP
ACCUMULATIONS.

CLOUD COVER WILL INCREASE THROUGH THIS AFTERNOON AND LOOKING AT MIN
TEMPS IN THE UPPER 30S TO MID 40S ACROSS THE CWA.

TOMORROW AND TOMORROW NIGHT...
AN UPPER LEVEL TROUGH MOVES OVER THE PLAINS TOMORROW MORNING AND THE
TROUGH PASSES OVER THE REGION TOMORROW NIGHT. THE UPPER LEVEL LOW
ASSOCIATED WITH THE TROUGH PASSES FARTHER NORTH...ALONG THE
US/CANADA BORDER.  THE SURFACE LOW ALSO BEGINS OVER THE PLAINS
THURSDAY MORNING AND THEN MOVES OVER IL THURSDAY EVENING. GUIDANCE
HAS THE LOW PROGRESSING A BIT SLOWER AND MADE THE NECESSARY
ADJUSTMENTS.

RAIN AND SOME STORMS MOVE IN FROM THE WEST THROUGH THE MORNING AND
EARLY AFTERNOON.  INSTABILITY IS NOT EXTREMELY IMPRESSIVE WITH THE
SYSTEM SO KEPT ONLY A CHANCE OF THUNDER. QPF AMOUNTS ON THE OTHER
HAND COULD BE IMPRESSIVE WITH TOTALS AROUND A HALF INCH OF RAIN.

WINDS WILL ALSO BE SHIFTING FROM SOUTHEAST IN THE MORNING TO OUT OF
THE WEST OVERNIGHT BEHIND THE LOW.  LOOKING AT A BREEZY AFTERNOON
WITH SOUTH WINDS GUSTING TO 35 MPH.  THE AMPLE WAA WILL LEAD TO MAX
TEMPS FROM AROUND 60 ALONG THE IL/WI BORDER TO THE UPPER 60S IF NOT
70 IN THE SOUTHERN CWA.

FRIDAY AND SATURDAY...
THE UPPER LEVEL LOW CONTINUES TO SHIFT EAST REACHING NEW ENGLAND BY
SATURDAY AFTERNOON/EVENING.  THE SURFACE LOW SHIFTS EAST AND
EXPECTING PRECIP TO COME TO AN END EARLY FRIDAY MORNING.  WEST WINDS
WILL BE GUSTING TO ARND 30 MPH FRIDAY AND AM THINKING THERE COULD BE
SOME DRY AIR MIXING DOWN TO THE SURFACE SO LOWERED DEWPOINTS A BIT.

THE AIR BEHIND THE COLD FRONT IS NOT REALLY ALL THAT COLD SINCE MAX
TEMPS ON FRIDAY LOOK TO BE AROUND 70 DEGREES.  A BACK DOOR COLD
FRONT SLIDES DOWN FROM THE NORTH IN THE EVENING. SOME GUIDANCE
MEMBERS FEATURE A BAND OF PRECIP FORMING AHEAD OF THE FRONT OVER FAR
NORTHERN IL AND NW INDIANA. PUT IN A CHANCE OF PRECIP SINCE FORCING
LOOKS GOOD...BUT HAVE LOW CONFIDENCE IN THE BAND OF PRECIP ACTUALLY
FORMING. AS SUCH KEPT POPS IN THE CHANCE RANGE.  WINDS TURN
NORTHEAST BEHIND THE FRONT AND OVERNIGHT LOWS WILL BE IN THE UPPER
30S TO MID 40S.

SOME GUIDANCE MEMBERS KEEP A BAND OF PRECIP OVER THE REGION SATURDAY
MORNING...BUT WITH HIGH PRESSURE MOVING OVER THE REGION HAVE LOW
CONFIDENCE AND WENT WITH A DRY FORECAST SATURDAY.  SKIES WILL CLEAR
BUT THE COOLER AIR OFF THE LAKE WILL RESULT IN HIGHS IN THE UPPER
40S TO MID 50S ALONG THE LAKE...AND THEN IN THE LOW TO MID 60S IN
THE OUTLYING AREAS.

GUIDANCE FEATURES PRECIP MOVING IN AHEAD OF THE NEXT LOW SATURDAY
NIGHT. HAVE LOW CONFIDENCE IN THIS ROUND OF PRECIP AS WELL...BUT
LEFT A CHANCE OF RAIN IN THE FORECAST.  OVERNIGHT LOWS WILL RANGE
FROM THE UPPER 30S TO THE MID 40S.

EXTENDED...SUNDAY THROUGH TUESDAY...
AN UPPER LEVEL CLOSED LOW SHIFTS OVER THE GREAT PLAINS SUNDAY
EVENING/NIGHT. GUIDANCE DIFFERS ON ITS EXACT PATH EARLY NEXT WEEK
BUT DOES HAVE THE UPPER LEVEL LOW OVER THE REGION THROUGH AT LEAST
MID WEEK.  ITS ASSOCIATED SURFACE LOW MOVES OVER THE PLAINS LATE
SUNDAY NIGHT/MONDAY MORNING AND SLIDES SOUTH OF THE CWA MONDAY
NIGHT. THE 12Z GUIDANCE AGREED A BIT MORE ABOUT THE SURFACE LOWS
PATH...AND HAVE IT MOVING THROUGH SOUTHERN IL TUESDAY.

IN TWO WORDS EARLY NEXT WEEK LOOKS CHILLY AND WET.  A BOUNDARY OVER
NORTHERN IL BRINGS THE LIFT FOR THE FIRST WAVE OF PRECIP EARLY ON
SUNDAY...BUT THEN MULTIPLE VORTICITY STREAMERS PASS THROUGH THE
REGION AS THE LOW SLOWLY SHIFTS EAST. THIS WILL RESULT IN A CHANCE
OF PRECIP THROUGHOUT THE EXTENDED. WILL INCLUDE A SLIGHT CHANCE OF
THUNDER ALONG AND SOUTH OF I-80 WHERE THERE WILL BE LIMITED ELEVATED
INSTABILITY BUT ENOUGH TO PERHAPS SUPPORT A COUPLE OF THUNDERSTORMS
SUNDAY NIGHT AND MONDAY. THE UPPER LEVEL JET DIPS FAR SOUTH THROUGH
TEXAS ALLOWING COOL AIR TO SPREAD ACROSS THE REGION. AS SUCH HIGHS
WILL VARY BETWEEN THE LOW 50S NORTH TO MID 60S SOUTH WITH A COOLING
TREND THROUGH TUESDAY.  LUCKILY OVERNIGHT LOWS LOOK LIKE THEY WILL
REMAIN ABOVE FREEZING.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* VARIABILITY IN THE WINDS REST OF THIS AFTERNOON FROM NNE TO ESE.
* CHANCE FOR SHOWERS THIS EVENING...THEN BETTER CHANCES FOR
  SHOWERS LATE THURSDAY AFTERNOON.
* WINDS VEERING TO SSE BY TOMORROW...THEN BECOMING VERY GUSTY LATE
  TOMORROW MORNING INTO THE AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST AWAY FROM THE
TERMINALS THIS AFTERNOON WITH WINDS CONTINUING TO VEER FROM THE
NORTHEAST EARLY THIS AFTERNOON TO THE SOUTHEAST OVERNIGHT. SHOWERS
CURRENTLY OVER SOUTHERN MINNESOTA AND IOWA MAY SKIRT THE IL/WI STATE
LINE LATE THIS AFTERNOON THROUGH LATE EVENING BRINGING A SMALL CHANCE
FOR SHOWERS. COVERAGE IS STILL UNCERTAIN SO WILL MAINTAIN PROB30 FOR
THE CHICAGO TERMINALS AND VCSH FOR RFD. MEANWHILE...LOW PRESSURE
WILL DEVELOP OVER THE SOUTHERN PLAINS AND LIFT TO THE MID
MISSISSIPPI VALLEY BY MIDDAY THURSDAY. THE GRADIENT WILL TIGHTEN
AHEAD OF THE LOW WITH GUSTS GRADUALLY INCREASING INTO THE UPPER 20
KT RANGE OT OF THE SSE...AND CANNOT RULE OUT SOME GUSTS IN EXCESS OF
30 KT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL THEN OVERSPREAD
THE TERMINALS MID TO LATE THURSDAY AFTERNOON.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION THIS AFTERNOON...MEDIUM-HIGH
  CONFIDENCE ON WIND DIRECTION/SPEED THURSDAY.
* LOW CONFIDENCE IN PRECIP AT TERMINALS THIS EVENING...MEDIUM
  CONFIDENCE IN PRECIP TIMING THURSDAY AFTERNOON.

BMD

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
219 PM CDT

PROGRESSIVE FLOW WILL CONTINUE THROUGH FRIDAY BEFORE A MUCH MORE
AMPLIFIED AND LOCKED PATTERN WILL SET UP FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK. THE HIGH PRESSURE PRESENTLY OVER THE LAKE WILL
BE SCOOTED EASTWARD EARLY FRIDAY AS LOW PRESSURE FROM THE CENTRAL
PLAINS BOOKS EASTWARD INTO NORTHERN INDIANA. DURING THURSDAY THIS
WILL PROVIDE STRONG SOUTHERLY FLOW. A FAIRLY STOUT INVERSION SHOULD
BE PRESENT OVER THE LAKE...BUT STRONG OFFSHORE WINDS IN NEARSHORE
AREAS SHOULD LEAD TO 25 TO POSSIBLE 30 KT GUSTS. AS A DEEP TROUGH
SETS UP ACROSS THE WESTERN U.S. AND SLOWLY MOVES EAST THROUGH THE
WEEKEND AND EARLY NEXT WEEK...SURFACE HIGH PRESSURE WILL GET
LOCKED OVER THE CENTRAL GREAT LAKES. A TIGHTENING PRESSURE
GRADIENT ON ITS SOUTHERN AND WESTERN SIDES WILL PROVIDE CONTINUOUS
EAST TO NORTHEAST SURFACE WINDS. THIS LOOKS LIKE A POTENTIAL
PROLONGED PERIOD OF SMALL CRAFT ADVISORY CRITERIA.

MTF

&&

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

&&

$$

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 231946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
246 PM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* VARIABILITY IN THE WINDS REST OF THIS AFTERNOON FROM NNE TO ESE.
* CHANCE FOR SHOWERS THIS EVENING...THEN BETTER CHANCES FOR
  SHOWERS LATE THURSDAY AFTERNOON.
* WINDS VEERING TO SSE BY TOMORROW...THEN BECOMING VERY GUSTY LATE
  TOMORROW MORNING INTO THE AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST AWAY FROM THE
TERMINALS THIS AFTERNOON WITH WINDS CONTINUING TO VEER FROM THE
NORTHEAST EARLY THIS AFTERNOON TO THE SOUTHEAST OVERNIGHT. SHOWERS
CURRENTLY OVER SOUTHERN MINNESOTA AND IOWA MAY SKIRT THE IL/WI STATE
LINE LATE THIS AFTERNOON THROUGH LATE EVENING BRINGING A SMALL CHANCE
FOR SHOWERS. COVERAGE IS STILL UNCERTAIN SO WILL MAINTAIN PROB30 FOR
THE CHICAGO TERMINALS AND VCSH FOR RFD. MEANWHILE...LOW PRESSURE
WILL DEVELOP OVER THE SOUTHERN PLAINS AND LIFT TO THE MID
MISSISSIPPI VALLEY BY MIDDAY THURSDAY. THE GRADIENT WILL TIGHTEN
AHEAD OF THE LOW WITH GUSTS GRADUALLY INCREASING INTO THE UPPER 20
KT RANGE OT OF THE SSE...AND CANNOT RULE OUT SOME GUSTS IN EXCESS OF
30 KT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL THEN OVERSPREAD
THE TERMINALS MID TO LATE THURSDAY AFTERNOON.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION THIS AFTERNOON...MEDIUM-HIGH
  CONFIDENCE ON WIND DIRECTION/SPEED THURSDAY.
* LOW CONFIDENCE IN PRECIP AT TERMINALS THIS EVENING...MEDIUM
  CONFIDENCE IN PRECIP TIMING THURSDAY AFTERNOON.

BMD

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
219 PM CDT

PROGRESSIVE FLOW WILL CONTINUE THROUGH FRIDAY BEFORE A MUCH MORE
AMPLIFIED AND LOCKED PATTERN WILL SET UP FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK. THE HIGH PRESSURE PRESENTLY OVER THE LAKE WILL
BE SCOOTED EASTWARD EARLY FRIDAY AS LOW PRESSURE FROM THE CENTRAL
PLAINS BOOKS EASTWARD INTO NORTHERN INDIANA. DURING THURSDAY THIS
WILL PROVIDE STRONG SOUTHERLY FLOW. A FAIRLY STOUT INVERSION SHOULD
BE PRESENT OVER THE LAKE...BUT STRONG OFFSHORE WINDS IN NEARSHORE
AREAS SHOULD LEAD TO 25 TO POSSIBLE 30 KT GUSTS. AS A DEEP TROUGH
SETS UP ACROSS THE WESTERN U.S. AND SLOWLY MOVES EAST THROUGH THE
WEEKEND AND EARLY NEXT WEEK...SURFACE HIGH PRESSURE WILL GET
LOCKED OVER THE CENTRAL GREAT LAKES. A TIGHTENING PRESSURE
GRADIENT ON ITS SOUTHERN AND WESTERN SIDES WILL PROVIDE CONTINUOUS
EAST TO NORTHEAST SURFACE WINDS. THIS LOOKS LIKE A POTENTIAL
PROLONGED PERIOD OF SMALL CRAFT ADVISORY CRITERIA.

MTF

&&

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

&&

$$

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 231919
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
219 PM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* CHANCE FOR SHOWERS THIS EVENING...THEN BETTER CHANCES FOR
  SHOWERS LATE THURSDAY AFTERNOON.
* WINDS VEERING TO SSE BY TOMORROW...THEN BECOMING VERY GUSTY LATE
  TOMORROW MORNING INTO THE AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST AWAY FROM THE
TERMINALS THIS AFTERNOON WITH WINDS CONTINUING TO VEER FROM THE
NORTHEAST EARLY THIS AFTERNOON TO THE SOUTHEAST OVERNIGHT. SHOWERS
CURRENTLY OVER SOUTHERN MINNESOTA AND IOWA MAY SKIRT THE IL/WI STATE
LINE LATE THIS AFTERNOON THROUGH LATE EVENING BRINGING A SMALL CHANCE
FOR SHOWERS. COVERAGE IS STILL UNCERTAIN SO WILL MAINTAIN PROB30 FOR
THE CHICAGO TERMINALS AND VCSH FOR RFD. MEANWHILE...LOW PRESSURE
WILL DEVELOP OVER THE SOUTHERN PLAINS AND LIFT TO THE MID
MISSISSIPPI VALLEY BY MIDDAY THURSDAY. THE GRADIENT WILL TIGHTEN
AHEAD OF THE LOW WITH GUSTS GRADUALLY INCREASING INTO THE UPPER 20
KT RANGE OT OF THE SSE...AND CANNOT RULE OUT SOME GUSTS IN EXCESS OF
30 KT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL THEN OVERSPREAD
THE TERMINALS MID TO LATE THURSDAY AFTERNOON.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION THIS AFTERNOON...MEDIUM-HIGH
  CONFIDENCE ON WIND DIRECTION/SPEED THURSDAY.
* LOW CONFIDENCE IN PRECIP AT TERMINALS THIS EVENING...MEDIUM
  CONFIDENCE IN PRECIP TIMING THURSDAY AFTERNOON.

BMD

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
219 PM CDT

PROGRESSIVE FLOW WILL CONTINUE THROUGH FRIDAY BEFORE A MUCH MORE
AMPLIFIED AND LOCKED PATTERN WILL SET UP FOR THE WEEKEND THROUGH THE
MIDDLE OF NEXT WEEK. THE HIGH PRESSURE PRESENTLY OVER THE LAKE WILL
BE SCOOTED EASTWARD EARLY FRIDAY AS LOW PRESSURE FROM THE CENTRAL
PLAINS BOOKS EASTWARD INTO NORTHERN INDIANA. DURING THURSDAY THIS
WILL PROVIDE STRONG SOUTHERLY FLOW. A FAIRLY STOUT INVERSION SHOULD
BE PRESENT OVER THE LAKE...BUT STRONG OFFSHORE WINDS IN NEARSHORE
AREAS SHOULD LEAD TO 25 TO POSSIBLE 30 KT GUSTS. AS A DEEP TROUGH
SETS UP ACROSS THE WESTERN U.S. AND SLOWLY MOVES EAST THROUGH THE
WEEKEND AND EARLY NEXT WEEK...SURFACE HIGH PRESSURE WILL GET
LOCKED OVER THE CENTRAL GREAT LAKES. A TIGHTENING PRESSURE
GRADIENT ON ITS SOUTHERN AND WESTERN SIDES WILL PROVIDE CONTINUOUS
EAST TO NORTHEAST SURFACE WINDS. THIS LOOKS LIKE A POTENTIAL
PROLONGED PERIOD OF SMALL CRAFT ADVISORY CRITERIA.

MTF

&&

.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 231737
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1237 PM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* CHANCE FOR SHOWERS THIS EVENING...THEN BETTER CHANCES FOR
  SHOWERS LATE THURSDAY AFTERNOON.
* WINDS VEERING TO SSE BY TOMORROW...THEN BECOMING VERY GUSTY LATE
  TOMORROW MORNING INTO THE AFTERNOON.

BMD

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST AWAY FROM THE
TERMINALS THIS AFTERNOON WITH WINDS CONTINUING TO VEER FROM THE
NORTHEAST EARLY THIS AFTERNOON TO THE SOUTHEAST OVERNIGHT. SHOWERS
CURRENTLY OVER SOUTHERN MINNESOTA AND IOWA MAY SKIRT THE IL/WI STATE
LINE LATE THIS AFTERNOON THROUGH LATE EVENING BRINGING A SMALL CHANCE
FOR SHOWERS. COVERAGE IS STILL UNCERTAIN SO WILL MAINTAIN PROB30 FOR
THE CHICAGO TERMINALS AND VCSH FOR RFD. MEANWHILE...LOW PRESSURE
WILL DEVELOP OVER THE SOUTHERN PLAINS AND LIFT TO THE MID
MISSISSIPPI VALLEY BY MIDDAY THURSDAY. THE GRADIENT WILL TIGHTEN
AHEAD OF THE LOW WITH GUSTS GRADUALLY INCREASING INTO THE UPPER 20
KT RANGE OT OF THE SSE...AND CANNOT RULE OUT SOME GUSTS IN EXCESS OF
30 KT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL THEN OVERSPREAD
THE TERMINALS MID TO LATE THURSDAY AFTERNOON.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION THIS AFTERNOON...MEDIUM-HIGH
  CONFIDENCE ON WIND DIRECTION/SPEED THURSDAY.
* LOW CONFIDENCE IN PRECIP AT TERMINALS THIS EVENING...MEDIUM
  CONFIDENCE IN PRECIP TIMING THURSDAY AFTERNOON.

BMD

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.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 231600
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1100 AM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* EAST-NORTHEAST WINDS WITH GUSTS TO AROUND 15 KT THROUGH
  EARLY/MID AFTERNOON.

* SCATTERED LIGHT SHOWERS POSSIBLE LATE TONIGHT.

RODRIGUEZ/DEUBELBEISS

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

WITH HIGH PRESSURE BUILDING OVERHEAD TODAY...EXPECT QUIET WEATHER
TO PERSIST. ALTHOUGH...THE TERMINALS REMAIN ON THE EASTERN FRINGE
OF THIS HIGH WITH SOME STRONGER WINDS STILL IN PLACE. NORTHEAST
WINDS WILL CONTINUE WITH GUSTS AROUND 15 KT LIKELY WITHIN THE NEXT
COUPLE OF HOURS. THESE GUSTS WILL LIKELY BE OBSERVED THROUGH MID
DAY...WITH A DIMINISHING TREND ANTICIPATED THIS AFTERNOON. WINDS
WILL TURN MORE EAST SOUTHEAST TONIGHT INTO THURSDAY WHILE
INCREASING AS THIS HIGH EXITS TO THE EAST AND A TROUGH OF LOW
PRESSURE APPROACHES FROM THE WEST. VFR CEILINGS WILL DEVELOP THIS
EVENING AND OVERNIGHT...WITH SHOWERS DEVELOPING MORE TOWARDS LATE
TONIGHT. ALTHOUGH...EXPECT THESE SHOWERS TO REMAIN RATHER LIGHT
WITH NO VIS RESTRICTION

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ/DEUBELBEISS

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.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 231400
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
900 AM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NORTHEAST WINDS WITH GUSTS TO AROUND 15 KT TODAY.

* SCATTERED LIGHT SHOWERS POSSIBLE LATE TONIGHT.

RODRIGUEZ/DEUBELBEISS

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

WITH HIGH PRESSURE BUILDING OVERHEAD TODAY...EXPECT QUIET WEATHER
TO PERSIST. ALTHOUGH...THE TERMINALS REMAIN ON THE EASTERN FRINGE
OF THIS HIGH WITH SOME STRONGER WINDS STILL IN PLACE. NORTHEAST
WINDS WILL CONTINUE WITH GUSTS AROUND 15 KT LIKELY WITHIN THE NEXT
COUPLE OF HOURS. THESE GUSTS WILL LIKELY BE OBSERVED THROUGH MID
DAY...WITH A DIMINISHING TREND ANTICIPATED THIS AFTERNOON. WINDS
WILL TURN MORE EAST SOUTHEAST TONIGHT INTO THURSDAY WHILE
INCREASING AS THIS HIGH EXITS TO THE EAST AND A TROUGH OF LOW
PRESSURE APPROACHES FROM THE WEST. VFR CEILINGS WILL DEVELOP THIS
EVENING AND OVERNIGHT...WITH SHOWERS DEVELOPING MORE TOWARDS LATE
TONIGHT. ALTHOUGH...EXPECT THESE SHOWERS TO REMAIN RATHER LIGHT
WITH NO VIS RESTRICTION

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ/DEUBELBEISS

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.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 231132
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
632 AM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

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

* NORTHEAST WINDS WITH GUSTS TO AROUND 15 KT TODAY.

* SCATTERED LIGHT SHOWERS POSSIBLE LATE TONIGHT.

RODRIGUEZ

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

WITH HIGH PRESSURE BUILDING OVERHEAD TODAY...EXPECT QUIET WEATHER
TO PERSIST. ALTHOUGH...THE TERMINALS REMAIN ON THE EASTERN FRINGE
OF THIS HIGH WITH SOME STRONGER WINDS STILL IN PLACE. NORTHEAST
WINDS WILL CONTINUE WITH GUSTS AROUND 15 KT LIKELY WITHIN THE NEXT
COUPLE OF HOURS. THESE GUSTS WILL LIKELY BE OBSERVED THROUGH MID
DAY...WITH A DIMINISHING TREND ANTICIPATED THIS AFTERNOON. WINDS
WILL TURN MORE EAST SOUTHEAST TONIGHT INTO THURSDAY WHILE
INCREASING AS THIS HIGH EXITS TO THE EAST AND A TROUGH OF LOW
PRESSURE APPROACHES FROM THE WEST. VFR CEILINGS WILL DEVELOP THIS
EVENING AND OVERNIGHT...WITH SHOWERS DEVELOPING MORE TOWARDS LATE
TONIGHT. ALTHOUGH...EXPECT THESE SHOWERS TO REMAIN RATHER LIGHT
WITH NO VIS RESTRICTION

RODRIGUEZ


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

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ

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

THURSDAY NIGHT...SHRA/MVFR LIKELY WITH A CHANCE OF TSRA.

FRIDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SATURDAY...SLIGHT CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

TUESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023 UNTIL 7 AM
     WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 7 AM
     WEDNESDAY.

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 230903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
403 AM CDT WED APR 23 2014

.DISCUSSION...
402 AM CDT

MAIN FORECAST CONCERNS THIS MORNING ARE WITH RELATIVELY LOW CHANCE
POPS FOR SHOWERS/SPRINKLES LATE THIS AFTERNOON/TONIGHT...THEN BETTER
POTENTIAL FOR RAIN AND A FEW THUNDERSTORMS THURSDAY/THURSDAY
EVENING  WITH APPROACHING SURFACE LOW PRESSURE WAVE PACIFIC COLD
FRONT. TEMPS LOOK MILD FOR FRIDAY BEHIND PACIFIC FRONT...BUT
COOLER/POTENTIALLY WET WEATHER STILL APPEARS TO DOMINATE EXTENDED
PERIODS OF FORECAST FROM THE WEEKEND INTO EARLY NEXT WEEK.

IN THE NEAR TERM...SURFACE HIGH PRESSURE RIDGE WAS OVER WISCONSIN
AND ILLINOIS EARLY THIS MORNING...PROVIDING COOL/DRY AND MAINLY
CLEAR CONDITIONS WITH LIGHT NORTH-NORTHEAST WINDS. A FEW SPOTS
DIPPING TO/BELOW THE FREEZING MARK...ESPECIALLY ACROSS THE FOX AND
ROCK RIVER VALLEY REGIONS THIS MORNING. FROST ADVISORY REMAINS IN
EFFECT THROUGH 7 AM CDT FOR MOST OF FAR NORTHERN/NORTHEAST IL AND
NORTHWEST IND. LOOKING AHEAD...EARLY MORNING GOES IMAGERY ALREADY
SHOWS HIGH CLOUDS INCREASING ACROSS THE PLAINS IN REGION OF WARM
ADVECTION IN ADVANCE OF WESTERN CONUS UPPER TROUGH. SHORT-TERM
MODELS REMAIN CONSISTENT IN BRINGING A WEAK MID-LEVEL SHORT WAVE
FROM THE CENTRAL PLAINS INTO OUR REGION THROUGH THIS EVENING...WITH
MID/UPPER LEVEL MOIST ADVECTION AND CONVERGENCE/FRONTOGENETIC
FORCING ALONG AN ELEVATED WARM FRONTAL ZONE EXPECTED TO PRODUCE SOME
HIGH BASED LIGHT SHOWERS/SPRINKLES INTO NORTH CENTRAL IL BY LATER
THIS AFTERNOON...AND ACROSS MUCH OF THE NORTH/NORTHWEST CWA TONIGHT
AS FORCING CONTINUES AHEAD OF A SECOND WEAK SHORT WAVE. HAVE
GENERALLY MAINTAINED HIGHEST POPS NORTHWEST OF I-88 CORRIDOR ACROSS
IL ALTHOUGH A FEW SHOWERS/SPRINKLES COULD OCCUR JUST ABOUT ANYWHERE
TONIGHT. PRECIP POTENTIAL INCREASES SIGNIFICANTLY THURSDAY AS MAIN
UPPER TROUGH APPROACHES FROM THE WEST...AND LOW LEVEL WINDS SHIFT
MORE SOUTHERLY AS A SURFACE LOW PRESSURE WAVE LIFTS FROM THE
MID-MISSOURI VALLEY NORTHEAST INTO WISCONSIN BY EVENING. NARROW
MOIST AXIS...COMBINED WITH INCREASING DEEP FORCING WITH APPROACH OF
SURFACE COLD FRONT AND LARGE SCALE ASCENT AHEAD OF UPPER TROUGH
SHOULD BE SUFFICIENT TO PRODUCE FAIRLY DECENT COVERAGE OF
RAIN/SHOWERS AND A FEW THUNDERSTORMS ESPECIALLY BY AFTERNOON.
OVERALL TREND OF GUIDANCE HAS BEEN TO SLOW ADVANCE OF COLD FRONT
SLIGHTLY...IN RESPONSE TO SLOWER PROGRESSION OF CLOSED LOW ALONG THE
CANADIAN BORDER. THUS HAVE HELD ONTO HIGHER POPS INTO THURSDAY
EVENING ESPECIALLY ACROSS THE EASTERN CWA...AS COLD FRONT COMPLETES
ITS TRANSIT.

TEMP WISE...EAST-NORTHEAST WINDS TODAY CONTINUE OUR COOLER THAN
NORMAL WEATHER PARTICULARLY ALONG LAKE MICHIGAN. HAVE GENERALLY GONE
WITH/SLIGHTLY ABOVE WARMER MAV NUMBERS WEST/SOUTHWEST WELL AWAY FROM
THE LAKE...THOUGH SHORE LOCATIONS WILL LIKELY NOT GET OUT OF THE 40S
AGAIN TODAY. COOL CONDITIONS CONTINUE TONIGHT ACROSS FAR NORTHEAST
IL WHERE CONTINUED EASTERLY COMPONENT AND LATER ARRIVAL OF THICKER
CLOUD COVER WILL ALLOW MINS TO DIP INTO THE MID-UPPER 30S. GRADUAL
VEERING OF LOW LEVEL WIND TO SOUTHEAST AND SLOW INCREASE IN LOW
LEVEL MOISTURE FROM THE SOUTH WILL HELP KEEP FAR SOUTHERN CWA ABOVE
40. MILDER SOUTHEAST FLOW THURSDAY WILL BE OFFSET BY CLOUDS/PRECIP
AND A CONTINUED SOUTHEAST WIND COMPONENT THROUGH THE MORNING...
THOUGH SHOULD SEE 60S ALL BUT IMMEDIATE NORTH SHORE AND LIKELY CLOSE
TO 70 SOUTH OF I-80. BREEZY/MILD BEHIND PACIFIC COLD FRONT THURSDAY
NIGHT INTO FRIDAY...WITH PERHAPS THE WARMEST TEMPS OF THIS FORECAST
PERIOD WITH GOOD MIXING AND WEST WINDS. LOW LEVEL THERMAL PROGS
SUPPORT GUIDANCE HIGHS FROM MID-UPPER 60S NORTH TO THE LOW 70S
SOUTH.

MODELS HAVE SHOWN SOME VARIATION/ADJUSTMENT WITH HANDLING OF LARGE
SCALE FLOW PATTERN AND RESULTING SYNOPTIC DETAILS FROM FRIDAY NIGHT
ONWARD. OVERALL...SLOWER CANADIAN BORDER SHORT WAVE PASSES NORTH OF
THE REGION FRIDAY...AND TRAILS A SECOND COLD FRONT SOUTH INTO THE
AREA BY EARLY EVENING. SOME POTENTIAL FOR SHOWERS ALONG THE FRONT
FRIDAY NIGHT...THOUGH GUIDANCE INCONSISTENT WITH TIMING/PLACEMENT OF
PRECIP AT THIS TIME AND FEEL SLIGHT CHANCE POPS SUFFICIENT AT THIS
TIME. COOL/DRY HIGH PRESSURE BUILDS ACROSS ONTARIO AND THE LAKES
INTO SATURDAY AS UPPER TROUGH CONTINUES OFF TO THE EAST. HIGHLY
AMPLIFIED TROUGH MOVES ACROSS WESTERN CONUS...WITH CLOSED LOW
DEVELOPING AND EVENTUALLY MOVING OUT ACROSS THE PLAINS
SUNDAY-TUESDAY. GULF MOISTURE IS EVENTUALLY DRAWN NORTH ACROSS LOW
LEVEL BAROCLINIC ZONE ASSOCIATED WITH WEST-EAST STATIONARY FRONT TO
OUR SOUTH...WITH INCREASING POTENTIAL FOR RAIN FROM THE SOUTHWEST
DURING THE PERIOD. COOL/DRY EAST-NORTHEAST FLOW FROM THE RETREATING
HIGH TO OUR NORTHEAST SHOULD SLOW THINGS A BIT...AND KEEP POPS
GRADUATED FROM LOWER NORTHEAST TO HIGHER SOUTHWEST. MODEL
DIFFERENCES IN DETAILS/TIMING OF EVOLUTION OF UPPER AND SURFACE LOWS
LATE IN THE PERIOD DIMINISH CONFIDENCE IN FINER DETAILS AT THIS
TIME.

RATZER

&&

.AVIATION...

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

* SCATTERED LIGHT SHOWERS POSSIBLE TOWARDS THE END OF THE FORECAST
  PERIOD.

RODRIGUEZ

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

LIGHT NORTHEAST WINDS WITH CLEAR SKIES IN PLACE...AND EXPECT WINDS
TO REMAIN NORTHEAST THROUGH MOST OF TODAY BEFORE TURNING MORE
EASTERLY LATER THIS EVENING AS VFR CEILINGS MOVE OVERHEAD.
SCATTERED LIGHT SHOWER DEVELOPMENT WILL MOVE ACROSS THE RFD AREA
LATE THIS AFTERNOON AND EARLY EVENING WITH THE REMAINING TERMINALS
LIKELY NOT OBSERVING THIS DEVELOPMENT UNTIL LATE IN THE EVENING.
ALTHOUGH...THESE SHOWERS WILL REMAIN RATHER LIGHT WITH NO VIS
RESTRICTION EXPECTED AT THIS TIME.

RODRIGUEZ

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

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023 UNTIL 7 AM
     WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 7 AM
     WEDNESDAY.

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 230811
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
311 AM CDT WED APR 23 2014

.DISCUSSION...
852 PM CDT

HAVE UPDATED HOURLY TEMPS TO ACCOUNT FOR A QUICKER FALL THIS
EVENING AND LOWERED MIN TEMPS A FEW DEGREES IN THE TYPICALLY
COLDER VALLEYS AND LOW LYING AREAS. ALSO...GIVEN THE CLEAR
SKIES...LIGHT WINDS...AND RECENT GREEN UP AND WARMTH...HAVE
THROWN OUT A FROST ADVISORY AWAY FROM THE URBANIZED AREAS OF
CHICAGO.

IZZI

//PREV DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

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

* SCATTERED LIGHT SHOWERS POSSIBLE TOWARDS THE END OF THE FORECAST
  PERIOD.

RODRIGUEZ

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

LIGHT NORTHEAST WINDS WITH CLEAR SKIES IN PLACE...AND EXPECT WINDS
TO REMAIN NORTHEAST THROUGH MOST OF TODAY BEFORE TURNING MORE
EASTERLY LATER THIS EVENING AS VFR CEILINGS MOVE OVERHEAD.
SCATTERED LIGHT SHOWER DEVELOPMENT WILL MOVE ACROSS THE RFD AREA
LATE THIS AFTERNOON AND EARLY EVENING WITH THE REMAINING TERMINALS
LIKELY NOT OBSERVING THIS DEVELOPMENT UNTIL LATE IN THE EVENING.
ALTHOUGH...THESE SHOWERS WILL REMAIN RATHER LIGHT WITH NO VIS
RESTRICTION EXPECTED AT THIS TIME.

RODRIGUEZ

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

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
310 AM CDT

AS THE LAKE REMAINS ON THE EASTERN FRINGE OF BUILDING HIGH
PRESSURE FROM THE WEST...NORTHWEST TO NORTH WINDS OF 10 TO 20 KT
REMAIN. ALTHOUGH...THIS HIGH WILL MOVE OVER THE LAKE TODAY WITH
SPEEDS DIMINISHING AND WITH WINDS LIKELY BECOMING MORE LIGHT AND
VARIABLE BY THE AFTERNOON. THEN AS THIS HIGH CONTINUES EAST
TONIGHT INTO THURSDAY AND A TROUGH OF LOW PRESSURE OVER THE
CENTRAL AND NORTHERN PLAINS MOVES EAST TOWARDS THE WESTERN GREAT
LAKES...EXPECT EAST TO SOUTHEAST WINDS TO INCREASE. SOUTHEAST
WINDS WILL FURTHER INCREASE ON THURSDAY BEFORE WINDS TURN TO THE
SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS THIS LOW PROGRESSES
THROUGH THE REGION.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023 UNTIL 7 AM
     WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 7 AM
     WEDNESDAY.

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 230535
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1235 AM CDT WED APR 23 2014

.DISCUSSION...
852 PM CDT

HAVE UPDATED HOURLY TEMPS TO ACCOUNT FOR A QUICKER FALL THIS
EVENING AND LOWERED MIN TEMPS A FEW DEGREES IN THE TYPICALLY
COLDER VALLEYS AND LOW LYING AREAS. ALSO...GIVEN THE CLEAR
SKIES...LIGHT WINDS...AND RECENT GREEN UP AND WARMTH...HAVE
THROWN OUT A FROST ADVISORY AWAY FROM THE URBANIZED AREAS OF
CHICAGO.

IZZI

//PREV DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

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

* SCATTERED LIGHT SHOWERS POSSIBLE TOWARDS THE END OF THE FORECAST
  PERIOD.

RODRIGUEZ

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

LIGHT NORTHEAST WINDS WITH CLEAR SKIES IN PLACE...AND EXPECT WINDS
TO REMAIN NORTHEAST THROUGH MOST OF TODAY BEFORE TURNING MORE
EASTERLY LATER THIS EVENING AS VFR CEILINGS MOVE OVERHEAD.
SCATTERED LIGHT SHOWER DEVELOPMENT WILL MOVE ACROSS THE RFD AREA
LATE THIS AFTERNOON AND EARLY EVENING WITH THE REMAINING TERMINALS
LIKELY NOT OBSERVING THIS DEVELOPMENT UNTIL LATE IN THE EVENING.
ALTHOUGH...THESE SHOWERS WILL REMAIN RATHER LIGHT WITH NO VIS
RESTRICTION EXPECTED AT THIS TIME.

RODRIGUEZ


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

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH VFR CONDITIONS.

RODRIGUEZ

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023 UNTIL 7 AM
     WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011 UNTIL 7 AM
     WEDNESDAY.

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 230259
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
959 PM CDT TUE APR 22 2014

.DISCUSSION...
852 PM CDT

HAVE UPDATED HOURLY TEMPS TO ACCOUNT FOR A QUICKER FALL THIS
EVENING AND LOWERED MIN TEMPS A FEW DEGREES IN THE TYPICALLY
COLDER VALLEYS AND LOW LYING AREAS. ALSO...GIVEN THE CLEAR
SKIES...LIGHT WINDS...AND RECENT GREEN UP AND WARMTH...HAVE
THROWN OUT A FROST ADVISORY AWAY FROM THE URBANIZED AREAS OF
CHICAGO.

IZZI

//PREV DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

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

* NONE

IZZI

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

VFR CIGS LIKELY TO DEVELOP AT OR ABOVE FL200 WEDNESDAY WITH
GRADUALLY LOWERING CIGS DURING AFTERNOON/EVENING. SOME SPOTTY
LIGHT SHRA OR VIRGA ARE POSSIBLE WEDNESDAY EVENING BUT KEPT OUT OF
TAFS SINCE CHANCES ARE LOW AND POTENTIAL IMPACT WOULD LIKELY BE
LOWER.

IZZI

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023...3 AM
     WEDNESDAY TO 7 AM WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011...3 AM WEDNESDAY TO
     7 AM WEDNESDAY.

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 230152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
852 PM CDT TUE APR 22 2014

.DISCUSSION...
852 PM CDT

HAVE UPDATED HOURLY TEMPS TO ACCOUNT FOR A QUICKER FALL THIS
EVENING AND LOWERED MIN TEMPS A FEW DEGREES IN THE TYPICALLY
COLDER VALLEYS AND LOW LYING AREAS. ALSO...GIVEN THE CLEAR
SKIES...LIGHT WINDS...AND RECENT GREEN UP AND WARMTH...HAVE
THROWN OUT A FROST ADVISORY AWAY FROM THE URBANIZED AREAS OF
CHICAGO.

IZZI

&&

.PREV DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

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

* NONE

IZZI

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

VFR CIGS LIKELY TO DEVELOP AT OR ABOVE FL200 WEDNESDAY WITH
GRADUALLY LOWERING CIGS DURING AFTERNOON/EVENING. SOME SPOTTY
LIGHT SHRA OR VIRGA ARE POSSIBLE WEDNESDAY EVENING BUT KEPT OUT OF
TAFS SINCE CHANCES ARE LOW AND POTENTIAL IMPACT WOULD LIKELY BE
LOWER.

IZZI

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ020-ILZ021-ILZ022-ILZ023...3 AM
     WEDNESDAY TO 7 AM WEDNESDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011...3 AM WEDNESDAY TO
     7 AM WEDNESDAY.

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 222301
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
601 PM CDT TUE APR 22 2014

.DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

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

* NONE

IZZI

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

VFR CIGS LIKELY TO DEVELOP AT OR ABOVE FL200 WEDNESDAY WITH
GRADUALLY LOWERING CIGS DURING AFTERNOON/EVENING. SOME SPOTTY
LIGHT SHRA OR VIRGA ARE POSSIBLE WEDNESDAY EVENING BUT KEPT OUT OF
TAFS SINCE CHANCES ARE LOW AND POTENTIAL IMPACT WOULD LIKELY BE
LOWER.

IZZI


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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

THURSDAY...SHRA/MVFR LIKELY IN EVENING WITH A CHANCE OF TSRA.

FRIDAY AND SATURDAY...GENERALLY VFR.

SUNDAY...CHANCE OF SHRA/TSRA...MAINLY AT NIGHT.

MONDAY...SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.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 222208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT TUE APR 22 2014

.DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NONE

IZZI

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE/IZZI

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.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 222031
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
331 PM CDT TUE APR 22 2014

.DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.


KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NE ARND 10 KT WITH GUSTS ARND 15 KT THIS AFTN.

* GUSTS DIMINISH THIS EVENING BUT WINDS REMAIN EAST THROUGH
  TOMORROW 5-9 KT.

JEE

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.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.TWITTER.COM/NWSCHICAGO
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000
FXUS63 KLOT 221954
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
254 PM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NE ARND 10 KT WITH GUSTS ARND 15 KT THIS AFTN.

* GUSTS DIMINISH THIS EVENING BUT WINDS REMAIN EAST THROUGH
  TOMORROW 5-9 KT.

JEE

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

.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 221942
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
242 PM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NE ARND 10 KT WITH GUSTS ARND 15 KT THIS AFTN.

* GUSTS DIMINISH THIS EVENING BUT WINDS REMAIN EAST THROUGH
  TOMORROW 5-9 KT.

JEE

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.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 221741
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 PM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE TURNS WINDS NE ARND 10 KT WITH GUSTS ARND 15 KT
  EARLY THIS AFTN.

* GUSTS DIMINISH THIS EVENING BUT WINDS REMAIN EAST THROUGH
  TOMORROW 5-9 KT.

JEE

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM HIGH CONFIDENCE FOR TIMING OF LAKE BREEZE...COULD BE
  LATER.

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 221553
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1053 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* LAKE BREEZE TURNS WINDS NE ARND 10 KT WITH GUSTS ARND 15 KT
  EARLY THIS AFTN...WITH WINDS TURNING AT MDW FIRST.

JEE

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

WITH HIGH PRESSURE BUILDING ACROSS THE TERMINALS THROUGH THE
FORECAST PERIOD...EXPECT RELATIVELY QUIET AND VFR CONDITIONS.
SURFACE WINDS HAVE TURNED BACK TO THE NORTHWEST AFTER BRIEFLY
BEING ORIENTED OUT OF THE NORTHEAST AFTER FROPA EARLIER THIS
MORNING. WITH THIS SURFACE PATTERN IN PLACE...FEEL THAT THESE
NORTHWEST/NORTH WINDS WILL NOT HAVE A PROBLEM TURNING TO THE
NORTHEAST BY MID DAY FOR ORD/MDW/GYY...WITH MDW AND GYY LIKELY
OBSERVING THIS SHIFT EARLIER. RFD/DPA WILL REMAIN NORTHWEST WITH
GUSTS INCREASING THROUGH MID TO LATE MORNING. THEN...ALL TERMINALS
WILL OBSERVE A NORTHEAST WIND BY LATER TODAY...PERSISTING THROUGH
THE REMAINDER OF THE FORECAST PERIOD.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM HIGH CONFIDENCE FOR TIMING OF LAKE BREEZE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 221359
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
859 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LAKE BREEZE TURNS WINDS NE ARND 10 KT WITH GUSTS ARND 15 KT
  EARLY THIS AFTN...WITH WINDS TURNING AT MDW FIRST.

JEE

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

WITH HIGH PRESSURE BUILDING ACROSS THE TERMINALS THROUGH THE
FORECAST PERIOD...EXPECT RELATIVELY QUIET AND VFR CONDITIONS.
SURFACE WINDS HAVE TURNED BACK TO THE NORTHWEST AFTER BRIEFLY
BEING ORIENTED OUT OF THE NORTHEAST AFTER FROPA EARLIER THIS
MORNING. WITH THIS SURFACE PATTERN IN PLACE...FEEL THAT THESE
NORTHWEST/NORTH WINDS WILL NOT HAVE A PROBLEM TURNING TO THE
NORTHEAST BY MID DAY FOR ORD/MDW/GYY...WITH MDW AND GYY LIKELY
OBSERVING THIS SHIFT EARLIER. RFD/DPA WILL REMAIN NORTHWEST WITH
GUSTS INCREASING THROUGH MID TO LATE MORNING. THEN...ALL TERMINALS
WILL OBSERVE A NORTHEAST WIND BY LATER TODAY...PERSISTING THROUGH
THE REMAINDER OF THE FORECAST PERIOD.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM HIGH CONFIDENCE FOR TIMING OF LAKE BREEZE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 221146
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
646 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

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

* NORTHWEST WINDS TURNING TO THE NORTHEAST BY MID DAY...SLIGHTLY
  EARLIER FOR MDW.

RODRIGUEZ

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

WITH HIGH PRESSURE BUILDING ACROSS THE TERMINALS THROUGH THE
FORECAST PERIOD...EXPECT RELATIVELY QUIET AND VFR CONDITIONS.
SURFACE WINDS HAVE TURNED BACK TO THE NORTHWEST AFTER BRIEFLY
BEING ORIENTED OUT OF THE NORTHEAST AFTER FROPA EARLIER THIS
MORNING. WITH THIS SURFACE PATTERN IN PLACE...FEEL THAT THESE
NORTHWEST/NORTH WINDS WILL NOT HAVE A PROBLEM TURNING TO THE
NORTHEAST BY MID DAY FOR ORD/MDW/GYY...WITH MDW AND GYY LIKELY
OBSERVING THIS SHIFT EARLIER. RFD/DPA WILL REMAIN NORTHWEST WITH
GUSTS INCREASING THROUGH MID TO LATE MORNING. THEN...ALL TERMINALS
WILL OBSERVE A NORTHEAST WIND BY LATER TODAY...PERSISTING THROUGH
THE REMAINDER OF THE FORECAST PERIOD.

RODRIGUEZ


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

* MEDIUM HIGH CONFIDENCE WITH WIND SHIFT TODAY.

RODRIGUEZ

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 220928
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
428 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

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

* NORTHEAST WINDS TURNING BACK TOWARDS THE NORTHWEST IN THE NEXT
  COUPLE OF HOURS...THEN TURNING BACK TO THE NORTHEAST BY MID DAY.

RODRIGUEZ

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

COLD FRONT CONTINUES TO SLOWLY DROP SOUTHEAST ACROSS THE AREA WITH
RFD ALREADY OBSERVING FROPA...WITH THE REMAINING TERMINALS LIKELY
OBSERVING FROPA WITHIN THE NEXT 1-2 HOURS AND THE WESTERLY WINDS
BECOMING MORE NORTHWEST/NORTH WHILE INCREASING. ALTHOUGH OUT AHEAD
OF THIS FRONT...RATHER MOIST CONDITIONS HAVE ALLOWED FOR FOG AND
LOW CEILINGS TO DEVELOP WITH VIS GENERALLY STAYING WITHIN THE
3-5SM RANGE. DO EXPECT FOG TO BE MORE OF A PREVAILING FEATURE
BEFORE FROPA AND AM NOT OVERLY CONCERNED WITH THE LOWER CEILINGS
BECOMING AN ISSUE. WITH FROPA...DRIER AIR ON THE BACKSIDE WILL
HELP SCOUR ANY FOG/LOW CLOUD COVER WITH VFR CONDITIONS THEN
EXPECTED FOR THE TERMINALS THROUGH THE REMAINING FORECAST PERIOD.
NORTHWEST WINDS WILL LIKELY INCREASE BY MID MORNING BUT WITH A
NORTHWEST/NORTH DIRECTION...WINDS SHOULD EASILY SHIFT TO THE
NORTHEAST FOR THE TERMINALS BY THE LAKE BY MID DAY AND REMAIN THIS
DIRECTION THROUGH THE END OF THE FORECAST PERIOD.

RODRIGUEZ

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

* MEDIUM CONFIDENCE WITH WINDS IN THE NEAR TERM.

RODRIGUEZ

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
427 AM CDT

AS LOW PRESSURE EXITED TO THE EAST OF THE LAKE OVERNIGHT...A FRONT
ON THE BACKSIDE PUSHED DOWN THE LAKE. THIS RESULTED IN WINDS
QUICKLY TURNING TO THE NORTHWEST/NORTH WHILE ALSO RAPIDLY
INCREASING. NORTHWEST WINDS TO 30 KT ARE STILL ONGOING AT THIS
TIME BUT EXPECT THEM TO DIMINISH THIS MORNING AND THROUGHOUT THE
DAY AS HIGH PRESSURE WELL TO THE WEST OF THE LAKE MOVES EAST TODAY
INTO WEDNESDAY. WITH THIS STRONGER NORTHERLY FLOW IN
PLACE...EXPECT BUILDING WAVES THIS MORNING TO RESULT IN HAZARDOUS
CONDITIONS FOR SMALL CRAFT IN THE NEARSHORE THROUGH THIS
AFTERNOON...BEFORE WAVES SUBSIDE INTO THE EVENING. DIMINISHING
WIND TREND WILL CONTINUE INTO WEDNESDAY AS THIS HIGH PRESSURE
MOVES OVERHEAD. A SLOW INCREASING TREND OUT OF THE SOUTHEAST WILL
ONCE AGAIN OCCUR WEDNESDAY NIGHT INTO THURSDAY AS NEW LOW PRESSURE
APPROACHES FROM THE WEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 220857
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
357 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

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

* NORTHEAST WINDS TURNING BACK TOWARDS THE NORTHWEST IN THE NEXT
  COUPLE OF HOURS...THEN TURNING BACK TO THE NORTHEAST BY MID DAY.

RODRIGUEZ

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

COLD FRONT CONTINUES TO SLOWLY DROP SOUTHEAST ACROSS THE AREA WITH
RFD ALREADY OBSERVING FROPA...WITH THE REMAINING TERMINALS LIKELY
OBSERVING FROPA WITHIN THE NEXT 1-2 HOURS AND THE WESTERLY WINDS
BECOMING MORE NORTHWEST/NORTH WHILE INCREASING. ALTHOUGH OUT AHEAD
OF THIS FRONT...RATHER MOIST CONDITIONS HAVE ALLOWED FOR FOG AND
LOW CEILINGS TO DEVELOP WITH VIS GENERALLY STAYING WITHIN THE
3-5SM RANGE. DO EXPECT FOG TO BE MORE OF A PREVAILING FEATURE
BEFORE FROPA AND AM NOT OVERLY CONCERNED WITH THE LOWER CEILINGS
BECOMING AN ISSUE. WITH FROPA...DRIER AIR ON THE BACKSIDE WILL
HELP SCOUR ANY FOG/LOW CLOUD COVER WITH VFR CONDITIONS THEN
EXPECTED FOR THE TERMINALS THROUGH THE REMAINING FORECAST PERIOD.
NORTHWEST WINDS WILL LIKELY INCREASE BY MID MORNING BUT WITH A
NORTHWEST/NORTH DIRECTION...WINDS SHOULD EASILY SHIFT TO THE
NORTHEAST FOR THE TERMINALS BY THE LAKE BY MID DAY AND REMAIN THIS
DIRECTION THROUGH THE END OF THE FORECAST PERIOD.

RODRIGUEZ

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

* MEDIUM CONFIDENCE WITH WINDS IN THE NEAR TERM.

RODRIGUEZ

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 220843
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
343 AM CDT TUE APR 22 2014

.DISCUSSION...
343 AM CDT

HIGHLIGHTS INCLUDE COOL/DRY CONDITIONS TODAY INTO WEDNESDAY...THEN
PRECIP POTENTIAL WITH NEXT LOW PRESSURE AND FRONTAL SYSTEM MOVING
THROUGH THE AREA THURSDAY. BRIEFLY MILD CONDITIONS FRIDAY...THEN
MUCH COOLER WEATHER AHEAD IN THE EXTENDED.

EARLY MORNING SURFACE ANALYSIS INDICATES COLD FRONT JUST CLEARING
FAR SOUTHEAST COUNTIES AT 08Z...WITH COOLER AND DRIER AIR PUSHING IN
ON NORTH-NORTHWEST WINDS BEHIND THE FRONT. SHOWERS HAVE MOVED EAST
OF THE CWA...WITH CLEARING SKIES FROM THE NORTHWEST PER GOES 11-3.9
MICRON IMAGERY. MOSTLY SUNNY...BREEZY AND COOLER CONDITIONS IN STORE
FOR TODAY IN POST-FRONTAL AIR MASS...WITH ONSHORE WINDS ALONG THE
LAKE KEEPING TEMPS EVEN COOLER NEAR THE LAKE. WHILE FAR
WEST/SOUTHWEST PARTS OF THE FORECAST AREA WILL LIKELY TOUCH THE 60
DEGREE MARK PER GUIDANCE...MID-40S TO MID-50S EXPECTED CLOSER TO THE
LAKE. SURFACE HIGH PRESSURE RIDGE MOVES INTO THE REGION TONIGHT AND
SETS THE STAGE FOR SOME CHILLY LATE APRIL MINS...AND HAVE MENTIONED
SOME PATCHY FROST ACROSS PARTS OF NORTHERN IL/NORTHWEST IND AWAY
FROM THE CITY. PATCHY FROST NOT AS LIKELY FAR WEST WHERE AN INCREASE
IN HIGH CLOUDS IS EXPECTED FROM THE WEST TOWARD MORNING.

SURFACE RIDGE MOVES OFF TO THE EAST ON WEDNESDAY...AS
SOUTH-SOUTHEAST WINDS INCREASE ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AHEAD OF AFOREMENTIONED TROUGH AND ASSOCIATED SURFACE LOW
PRESSURE DEVELOPING ACROSS THE PLAINS. EASTERLY COMPONENT OF LOW
LEVEL FLOW MAINTAINS DRY AIR ACROSS THE WESTERN LAKES WEDNESDAY AS
INDICATED BY DRY TIME/HEIGHT SECTIONS. SHALLOW MIXING AND EAST
SURFACE WINDS DO NOT SUPPORT MUCH WARMING OVER TODAYS TEMPS...AND
LOOKS EVEN A FEW DEGREES COOLER ACROSS PARTS OF NORTH/NORTHEAST IL.
MODELS STEADFAST IN DEVELOPING PRECIP ACROSS AREA BY WEDNESDAY
AFTERNOON...THOUGH APPEARS QPF IS OVERDONE AND SUSPECT MAINLY JUST
SOME LIGHT SHOWERS/SPRINKLES FROM MID-LEVEL CLOUD BASES WEDNESDAY
AFTERNOON INTO WEDNESDAY NIGHT WITH ELEVATED WARM FRONT. MUCH BETTER
RAIN CHANCES ARRIVE ON THURSDAY AS UPPER TROUGH APPROACHES AND LOW
LEVEL WINDS TURN SOUTHERLY AND SPREAD PRE-COLD FRONTAL MOISTURE AXIS
INTO THE FORECAST AREA. WRF/SREF ARE QUICKER TO MOVE FRONT THROUGH
THURSDAY AFTERNOON...BUT PREFER THE CONSISTENTLY SLOWER SOLUTION
FROM THE GLOBAL ECMWF/GFS/GEM WHICH BRING THE FRONT THROUGH A FEW
HOURS SLOWER. IN ANY CASE...BEST PRECIP POTENTIAL SHOULD BE
ASSOCIATED WITH LOW LEVEL MOISTURE POOL ALONG AND AHEAD OF THE FRONT
AND MAINTAINED HIGHEST POPS THURSDAY/THURSDAY EVENING WITH THE ITS
PASSAGE. MODEST LAPSE RATES 6.5-7.0 C/KM ABOVE BOUNDARY LAYER WILL
LIKELY SUPPORT AT LEAST SCATTERED THUNDERSTORMS DURING PERIOD OF
BEST FORCING AHEAD OF THE FRONT. SOUTH-SOUTHEAST WINDS DO PRODUCE
SOME WARMING IN THE TEMP DEPARTMENT...THOUGH SLIGHT EAST COMPONENT
FOR PART OF THE DAY COMBINED WITH CLOUDS/PRECIP AND FAIRLY SHALLOW
BOUNDARY LAYER PER MODEL SOUNDINGS SUGGEST A REPEAT OF THIS
WEEKEND/S 70S/80 IS UNLIKELY. THERMAL FIELDS INDICATE 65-70 FOR
HIGHS ACROSS MUCH OF THE AREA...WITH LOWER 60S CLOSER TO THE IL/WI
BORDER.

LONGER RANGE GUIDANCE SOLUTIONS IN GENERAL AGREEMENT THAT UPPER
TROUGH WILL CLOSE OFF OVER THE NORTHERN LAKES THURSDAY NIGHT INTO
FRIDAY...WITH ANOTHER STRONG VORT WRAPPING AROUND THE SOUTHERN
PERIPHERY OF THE CLOSED UPPER LOW FRIDAY. INITIAL FRONTAL PASSAGE
LATER THURSDAY IS OF PACIFIC NATURE...WITH MILD WESTERLY FLOW FRIDAY
ALLOWING TEMPS BACK INTO THE MID 60S-LOW 70S RANGE. SECONDARY VORT
BRINGS ABOUT PASSAGE OF STRONGER COLD FRONT FROM THE NORTH WITH THE
POTENTIAL FOR A FEW SHOWERS BY LATE FRIDAY HOWEVER...STARTING THE
TRANSITION TO A COOLER REGIME WHICH LOOKS TO LINGER THROUGH THE
WEEKEND AND EARLY NEXT WEEK. EXTENDED GUIDANCE IN CLOSE AGREEMENT IN
DEVELOPING SLOW-MOVING CLOSED LOW OVER THE PLAINS AND SLOWING OUR
PREVIOUSLY PROGRESSIVE FLOW. COLD FRONT BECOMES STATIONARY ACROSS
THE OHIO VALLEY TO OUR SOUTH...WITH COOL HIGH PRESSURE ANCHORED
NORTH OF THE LAKES. COOL/DRY EASTERLY FLOW PREVAILS SATURDAY THROUGH
MONDAY...THOUGH SOME POTENTIAL FOR PRECIP DOES EXIST BENEATH
ELEVATED BAROCLINIC ZONE ASSOCIATED WITH STALLED FRONT TO OUR
SOUTH...ESPECIALLY LATER IN THE PERIOD (SUN-MON). EAST-NORTHEAST LOW
LEVEL WIND REGIME SUPPORTS WELL BELOW NORMAL TEMPS WITH HIGHS IN THE
40S/50S AND LOWS IN THE 30S. REMAINDER OF WEEK LOOKS SIMILARLY COOL
AS UPPER LOW VERY SLOWLY TRANSITS THE MIDWEST.

RATZER

&&

.AVIATION...

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

* FROPA WITHIN THE NEXT 1-2 HOURS.

* PATCHY FOG BEFORE FROPA.

* NORTHWEST WINDS TURNING TO THE NORTHEAST BY MID DAY.

RODRIGUEZ

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

COLD FRONT CONTINUES TO SLOWLY DROP SOUTHEAST ACROSS THE AREA WITH
RFD ALREADY OBSERVING FROPA...WITH THE REMAINING TERMINALS LIKELY
OBSERVING FROPA WITHIN THE NEXT 1-2 HOURS AND THE WESTERLY WINDS
BECOMING MORE NORTHWEST/NORTH WHILE INCREASING. ALTHOUGH OUT AHEAD
OF THIS FRONT...RATHER MOIST CONDITIONS HAVE ALLOWED FOR FOG AND
LOW CEILINGS TO DEVELOP WITH VIS GENERALLY STAYING WITHIN THE
3-5SM RANGE. DO EXPECT FOG TO BE MORE OF A PREVAILING FEATURE
BEFORE FROPA AND AM NOT OVERLY CONCERNED WITH THE LOWER CEILINGS
BECOMING AN ISSUE. WITH FROPA...DRIER AIR ON THE BACKSIDE WILL
HELP SCOUR ANY FOG/LOW CLOUD COVER WITH VFR CONDITIONS THEN
EXPECTED FOR THE TERMINALS THROUGH THE REMAINING FORECAST PERIOD.
NORTHWEST WINDS WILL LIKELY INCREASE BY MID MORNING BUT WITH A
NORTHWEST/NORTH DIRECTION...WINDS SHOULD EASILY SHIFT TO THE
NORTHEAST FOR THE TERMINALS BY THE LAKE BY MID DAY AND REMAIN THIS
DIRECTION THROUGH THE END OF THE FORECAST PERIOD.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH FROPA...AND WIND SHIFT LATER TODAY.

* HIGH CONFIDENCE WITH FOG EARLY THIS MORNING.

RODRIGUEZ

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 220540
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1240 AM CDT TUE APR 22 2014

.DISCUSSION...
858 PM CDT

HAVE DONE SOME MAINLY COSMETIC WORK TO POP/WX TO TIME THE SHOWERS
ENDING THIS EVENING AS TROUGH AXIS SHIFTS EAST OF THE AREA. CLOUD
COVER AND WESTERLY WINDS SHOULD ALLOW TEMPS TO HOLD IN THE LOW/MID
60S UNTIL FROPA OVERNIGHT. SPEAKING OF WHICH...COLD FRONT FROM NE
WI SOUTHWEST TO KUIN WILL SWEEP ACROSS THE CWA OVERNIGHT CAUSING
WINDS TO SHIFT TO NNW. THE WIND DIRECTION AND RESEVOUR OF VERY
COLD AIR OVER THE LAKE SHOULD RESULT IN SOME LAKE ENHANCEMENT TO
THE FRONT OVER NE IL AND NW IN WITH A VERY RAPID DROP IN
TEMPERATURES OVERNIGHT AND HAVE NUDGED TEMPS DOWNWARD IN THE GRIDS
AND ATTEMPTED TO ACCOUNT FOR THIS MORE RAPID DROP IN THE HOURLY
TEMP GRIDS. THE NORTHERLY WINDS OFF THE LAKE SHOULD RESULT IN
TEMPS LAKESIDE HOLDING IN THE 40S TOMORROW.

IZZI

//PREV DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

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

* FROPA WITHIN THE NEXT 1-2 HOURS.

* PATCHY FOG BEFORE FROPA.

* NORTHWEST WINDS TURNING TO THE NORTHEAST BY MID DAY.

RODRIGUEZ

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

COLD FRONT CONTINUES TO SLOWLY DROP SOUTHEAST ACROSS THE AREA WITH
RFD ALREADY OBSERVING FROPA...WITH THE REMAINING TERMINALS LIKELY
OBSERVING FROPA WITHIN THE NEXT 1-2 HOURS AND THE WESTERLY WINDS
BECOMING MORE NORTHWEST/NORTH WHILE INCREASING. ALTHOUGH OUT AHEAD
OF THIS FRONT...RATHER MOIST CONDITIONS HAVE ALLOWED FOR FOG AND
LOW CEILINGS TO DEVELOP WITH VIS GENERALLY STAYING WITHIN THE
3-5SM RANGE. DO EXPECT FOG TO BE MORE OF A PREVAILING FEATURE
BEFORE FROPA AND AM NOT OVERLY CONCERNED WITH THE LOWER CEILINGS
BECOMING AN ISSUE. WITH FROPA...DRIER AIR ON THE BACKSIDE WILL
HELP SCOUR ANY FOG/LOW CLOUD COVER WITH VFR CONDITIONS THEN
EXPECTED FOR THE TERMINALS THROUGH THE REMAINING FORECAST PERIOD.
NORTHWEST WINDS WILL LIKELY INCREASE BY MID MORNING BUT WITH A
NORTHWEST/NORTH DIRECTION...WINDS SHOULD EASILY SHIFT TO THE
NORTHEAST FOR THE TERMINALS BY THE LAKE BY MID DAY AND REMAIN THIS
DIRECTION THROUGH THE END OF THE FORECAST PERIOD.

RODRIGUEZ


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

* MEDIUM HIGH CONFIDENCE WITH FROPA...AND WIND SHIFT LATER TODAY.

* HIGH CONFIDENCE WITH FOG EARLY THIS MORNING.

RODRIGUEZ

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 220312
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1012 PM CDT MON APR 21 2014

.DISCUSSION...
858 PM CDT

HAVE DONE SOME MAINLY COSMETIC WORK TO POP/WX TO TIME THE SHOWERS
ENDING THIS EVENING AS TROUGH AXIS SHIFTS EAST OF THE AREA. CLOUD
COVER AND WESTERLY WINDS SHOULD ALLOW TEMPS TO HOLD IN THE LOW/MID
60S UNTIL FROPA OVERNIGHT. SPEAKING OF WHICH...COLD FRONT FROM NE
WI SOUTHWEST TO KUIN WILL SWEEP ACROSS THE CWA OVERNIGHT CAUSING
WINDS TO SHIFT TO NNW. THE WIND DIRECTION AND RESEVOUR OF VERY
COLD AIR OVER THE LAKE SHOULD RESULT IN SOME LAKE ENHANCEMENT TO
THE FRONT OVER NE IL AND NW IN WITH A VERY RAPID DROP IN
TEMPERATURES OVERNIGHT AND HAVE NUDGED TEMPS DOWNWARD IN THE GRIDS
AND ATTEMPTED TO ACCOUNT FOR THIS MORE RAPID DROP IN THE HOURLY
TEMP GRIDS. THE NORTHERLY WINDS OFF THE LAKE SHOULD RESULT IN
TEMPS LAKESIDE HOLDING IN THE 40S TOMORROW.

IZZI

//PREV DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

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

* WEST TO AT TIMES SOUTHWEST WINDS UNTIL FRONTAL BOUNDARY
  ARRIVES...THEN WINDS QUICKLY SHIFT TO NORTHWEST THEN NORTH BY
  06Z. WIND SPEEDS WILL INCREASE AS WELL WITH GUSTS OVERNIGHT TO
  20KT.

* WINDS TURN NORTHEAST EARLY TUE AFTN WITH CONTINUED GUSTS TO
  20KT.

BEACHLER

//DISCUSSION...UPDATED 03Z...

PRECIP HAS ENDED ACROSS THE TAF SITES...HOWEVER THE FRONTAL
BOUNDARY HAS SLOWED IN ARRIVAL. WITH LIGHT WINDS AND VERY MOIST
CONDITIONS REMAINING AHEAD OF THE BOUNDARY...PATCHY FOG HAS
DEVELOPED. EXPECT THIS TO QUICKLY DISSIPATE BETWEEN 5-7Z ONCE THE
FRONTAL BOUNDARY ARRIVES AND USHERS IN MUCH DRIER AIR.


PREVIOUS DISCUSSION UPDATED 00Z...

ISOLATED SHOWERS AND THUNDERSTORMS HAVE STEADILY DISSIPATED THIS
EVENING AND SHOULD COME TO AN END ARND 130Z FOR ORD...AND CLOSER
TO 2Z AT MDW/GYY. THIS WILL BE ASSOCIATED WITH THE FRONTAL
BOUNDARY ARRIVAL...WHICH WILL BRING A WIND SHIFT FROM SOUTHWEST TO
NORTHWEST AND EVENTUALLY NORTH BY 05-06Z. IN ADDITION THE GRADIENT
DOES REMAIN TIGHT WITH THE BOUNDARY PASSAGE...AND EXPECT FREQUENT
GUSTS TO PERSIST THROUGH THE OVERNIGHT AND LIKELY THRU MUCH OF
TUE. GUSTS SHUD GENERALLY BE BETWEEN 18-24KT. THEN AS HIGH
PRESSURE STEADILY PUSHES SOUTHEAST INTO THE UPPER MIDWEST...WINDS
MAY BEGIN TO TURN NORTHEAST EARLY TUE AFTN...WHICH COULD PRODUCE
DIRECTIONS OVER TO 020-040 DEG.

SKIES WILL ALSO IMPROVE THIS EVENING AS THE FRONTAL BOUNDARY
SLIDES EAST ACROSS THE NORTHERN IL/NORTHWEST IN AIRFIELDS. A RUSH
OF DRIER AIR WILL QUICKLY ERODE THE CLOUDS...AND BRING VFR CONDS
WITH JUST SOME THIN CLOUDS AT 8-10KFT AGL OVERNIGHT.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR SHIFT TO NORTHWEST/NORTH...MEDIUM
  CONFIDENCE IN PRECISE TIMING OF WIND SHIFT.

* HIGH CONFIDENCE IN ALL OTHER ELEMENTS.

BEACHLER

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM TUESDAY.

&&

$$

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 220158
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
858 PM CDT MON APR 21 2014

.DISCUSSION...
858 PM CDT

HAVE DONE SOME MAINLY COSMETIC WORK TO POP/WX TO TIME THE SHOWERS
ENDING THIS EVENING AS TROUGH AXIS SHIFTS EAST OF THE AREA. CLOUD
COVER AND WESTERLY WINDS SHOULD ALLOW TEMPS TO HOLD IN THE LOW/MID
60S UNTIL FROPA OVERNIGHT. SPEAKING OF WHICH...COLD FRONT FROM NE
WI SOUTHWEST TO KUIN WILL SWEEP ACROSS THE CWA OVERNIGHT CAUSING
WINDS TO SHIFT TO NNW. THE WIND DIRECTION AND RESEVOUR OF VERY
COLD AIR OVER THE LAKE SHOULD RESULT IN SOME LAKE ENHANCEMENT TO
THE FRONT OVER NE IL AND NW IN WITH A VERY RAPID DROP IN
TEMPERATURES OVERNIGHT AND HAVE NUDGED TEMPS DOWNWARD IN THE GRIDS
AND ATTEMPTED TO ACCOUNT FOR THIS MORE RAPID DROP IN THE HOURLY
TEMP GRIDS. THE NORTHERLY WINDS OFF THE LAKE SHOULD RESULT IN
TEMPS LAKESIDE HOLDING IN THE 40S TOMORROW.

IZZI

&&

.PREV DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

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

* ISOLATED THUNDERSTORMS QUICKLY DISSIPATING BY 0045Z AT
  MDW...WITH JUST A LINGERING SHRA THRU 2Z.

* ORD WILL SEE AN ISOLATED SHRA THRU 0130Z.

* WEST TO AT TIMES SOUTHWEST WINDS UNTIL FRONTAL BOUNDARY
  ARRIVES...THEN WINDS QUICKLY SHIFT TO NORTHWEST THEN NORTH BY
  06Z. WIND SPEEDS WILL INCREASE AS WELL WITH GUSTS OVERNIGHT TO
  20KT.

* WINDS TURN NORTHEAST EARLY TUE AFTN WITH CONTINUED GUSTS TO
  20KT.

BEACHLER

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

ISOLATED SHOWERS AND THUNDERSTORMS HAVE STEADILY DISSIPATED THIS
EVENING AND SHOULD COME TO AN END ARND 130Z FOR ORD...AND CLOSER
TO 2Z AT MDW/GYY. THIS WILL BE ASSOCIATED WITH THE FRONTAL
BOUNDARY ARRIVAL...WHICH WILL BRING A WIND SHIFT FROM SOUTHWEST TO
NORTHWEST AND EVENTUALLY NORTH BY 05-06Z. IN ADDITION THE GRADIENT
DOES REMAIN TIGHT WITH THE BOUNDARY PASSAGE...AND EXPECT FREQUENT
GUSTS TO PERSIST THROUGH THE OVERNIGHT AND LIKELY THRU MUCH OF
TUE. GUSTS SHUD GENERALLY BE BETWEEN 18-24KT. THEN AS HIGH
PRESSURE STEADILY PUSHES SOUTHEAST INTO THE UPPER MIDWEST...WINDS
MAY BEGIN TO TURN NORTHEAST EARLY TUE AFTN...WHICH COULD PRODUCE
DIRECTIONS OVER TO 020-040 DEG.

SKIES WILL ALSO IMPROVE THIS EVENING AS THE FRONTAL BOUNDARY
SLIDES EAST ACROSS THE NORTHERN IL/NORTHWEST IN AIRFIELDS. A RUSH
OF DRIER AIR WILL QUICKLY ERODE THE CLOUDS...AND BRING VFR CONDS
WITH JUST SOME THIN CLOUDS AT 8-10KFT AGL OVERNIGHT.

BEACHLER

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

* HIGH CONFIDENCE IN PRECIP/THUNDER ENDING BY 2Z AT TAF SITES.

* HIGH CONFIDENCE IN WIND DIR SHIFT TO NORTHWEST/NORTH...MEDIUM
  CONFIDENCE IN PRECISE TIMING OF WIND SHIFT.

* HIGH CONFIDENCE IN ALL OTHER ELEMENTS.

BEACHLER

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM TUESDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 AM TUESDAY.

&&

$$

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 220008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
708 PM CDT MON APR 21 2014

.DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

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

* ISOLATED THUNDERSTORMS QUICKLY DISSIPATING BY 0045Z AT
  MDW...WITH JUST A LINGERING SHRA THRU 2Z.

* ORD WILL SEE AN ISOLATED SHRA THRU 0130Z.

* WEST TO AT TIMES SOUTHWEST WINDS UNTIL FRONTAL BOUNDARY
  ARRIVES...THEN WINDS QUICKLY SHIFT TO NORTHWEST THEN NORTH BY
  06Z. WIND SPEEDS WILL INCREASE AS WELL WITH GUSTS OVERNIGHT TO
  20KT.

* WINDS TURN NORTHEAST EARLY TUE AFTN WITH CONTINUED GUSTS TO
  20KT.

BEACHLER

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

ISOLATED SHOWERS AND THUNDERSTORMS HAVE STEADILY DISSIPATED THIS
EVENING AND SHOULD COME TO AN END ARND 130Z FOR ORD...AND CLOSER
TO 2Z AT MDW/GYY. THIS WILL BE ASSOCIATED WITH THE FRONTAL
BOUNDARY ARRIVAL...WHICH WILL BRING A WIND SHIFT FROM SOUTHWEST TO
NORTHWEST AND EVENTUALLY NORTH BY 05-06Z. IN ADDITION THE GRADIENT
DOES REMAIN TIGHT WITH THE BOUNDARY PASSAGE...AND EXPECT FREQUENT
GUSTS TO PERSIST THROUGH THE OVERNIGHT AND LIKELY THRU MUCH OF
TUE. GUSTS SHUD GENERALLY BE BETWEEN 18-24KT. THEN AS HIGH
PRESSURE STEADILY PUSHES SOUTHEAST INTO THE UPPER MIDWEST...WINDS
MAY BEGIN TO TURN NORTHEAST EARLY TUE AFTN...WHICH COULD PRODUCE
DIRECTIONS OVER TO 020-040 DEG.

SKIES WILL ALSO IMPROVE THIS EVENING AS THE FRONTAL BOUNDARY
SLIDES EAST ACROSS THE NORTHERN IL/NORTHWEST IN AIRFIELDS. A RUSH
OF DRIER AIR WILL QUICKLY ERODE THE CLOUDS...AND BRING VFR CONDS
WITH JUST SOME THIN CLOUDS AT 8-10KFT AGL OVERNIGHT.

BEACHLER


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

* HIGH CONFIDENCE IN PRECIP/THUNDER ENDING BY 2Z AT TAF SITES.

* HIGH CONFIDENCE IN WIND DIR SHIFT TO NORTHWEST/NORTH...MEDIUM
  CONFIDENCE IN PRECISE TIMING OF WIND SHIFT.

* HIGH CONFIDENCE IN ALL OTHER ELEMENTS.

BEACHLER

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

WEDNESDAY...CHC OF SHOWERS. OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHC OF SHOWERS EARLY. MAINLY VFR.

SATURDAY THROUGH SUNDAY...SLIGHT CHANCE OF SHOWERS. MAINLY VFR.

BEACHLER

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 PM MONDAY TO 3
     PM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 PM MONDAY TO 10
     AM TUESDAY.

&&

$$

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 212216
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
516 PM CDT MON APR 21 2014

.DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* SHRA WITH ISOLATED/SCATTERED TSRA THROUGH MID-EVE.
* CHANCE FOR A BRIEF PERIOD OF MVFR CIGS EARLY THIS EVE.
* WEST/SOUTHWEST WINDS THIS AFTERNOON BECOMING NORTHWEST BY
  EARLY-MID EVE
* WINDS BECOMING NORTHEAST TUESDAY AFTERNOON.

//DISCUSSION...UPDATED 18Z...

BROAD LOW PRESSURE ACROSS WI/U.P. OF MICHIGAN WILL CONSOLIDATE
GOING INTO THIS EVE AND STEER A COLD FRONT ACROSS THE AREA EARLY
THIS EVE. AHEAD OF THIS...FORCING AND MOISTURE WILL BE ENOUGH TO
CONTINUE AREAS OF SHOWERS. THERE LIKELY WILL BE AN UPTICK IN
COVERAGE DURING THE MID-LATE AFTERNOON ACROSS NORTHERN/CENTRAL
IL. HOW MUCH THUNDER IS EMBEDDED IN THAT REMAINS SOMEWHAT
UNCERTAIN...BUT IT LIKELY TO BE ON THE ORDER OF 30-50 PERCENT.
HAVE TRENDED TO A VCTS FOR THAT REASON. IN SOME OF THE MORE MODEST
SHOWERS NEAR THE FRONT THERE HAVE BEEN OBSERVATIONS OF BRIEF IFR
VISIBILITY TO THE WEST AND FEEL THAT COVERAGE OF AT LEAST SHOWERS
AHEAD OF THE FRONT WILL BE HIGH ENOUGH HERE TO MAINTAIN THAT 3SM
MENTION IN THE TAFS. MVFR CIGS ARE LESS COMMON SO HAVE NOT
INCLUDED IN TAFS. WITH FROPA THIS EVE WILL COME DRYING ALONG WITH
NORTHWEST GUSTS WHICH ARE FAVORED TO LAST INTO THE DAY TUESDAY.
GIVEN THE NNW TRAJECTORY OF SYNOPTIC SURFACE WINDS AND THE
DIMINISHING SPEEDS BY MIDDAY TUE...CLIMATOLOGY WILL LIKELY TAKE
OVER FOR A NORTHEAST WIND TO DEVELOP OFF THE LAKE AT ORD AND MDW.

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH IN SHRA OCCURRING AND WINDS REMAINING BETWEEN 260 AND 300
  THROUGH EARLY EVE INCLUDING UNDER AND NEAR SHRA.
* LOW IN TSRA OCCURRING AT THE AIRFIELDS THEMSELVES. HIGH IN
  TIMING IF THEY DO OCCUR BETWEEN BETWEEN 22Z-01Z.
* LOW IN WHETHER MVFR CIGS CAN DEVELOP.
* HIGH IN WIND SHIFT TO NORTHEAST TUESDAY AFTERNOON BUT LOW IN
  TIMING.

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MTF/RODRIGUEZ

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 PM MONDAY TO 3
     PM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 PM MONDAY TO 10
     AM TUESDAY.

&&

$$

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 212013
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
313 PM CDT MON APR 21 2014

.DISCUSSION...
313 PM CDT

FOR THE REST OF THIS AFTERNOON AND TONIGHT...THE MAIN FOCUS WILL
CONTINUE TO BE THE DEVELOPING CONVECTION IN THE WARM SECTOR AHEAD OF
A COLD FRONT.  AT 2PM...THE COLD FRONT EXTENDS FROM CENTRAL
WISCONSIN THROUGH EASTERN IOWA.  A PRE-FRONTAL TROUGH HAS FORMED IN
THE WARM SECTOR AHEAD OF THE MAIN COLD FRONT...WHICH IS MOVING
THROUGH NORTHEASTERN ILLINOIS.  THE BULK OF THE THUNDERSTORM
ACTIVITY HAS FORMED EITHER ALONG THE  OR IN THE
BROAD AREA OF ISENTROPIC LIFT ACROSS NRN IL/NWRN IN IN THE WARM
SECTOR.  SFC DEWPOINTS ARE FINALLY RISING INTO THE LOWER TO MIDDLE
50S BEHIND THE PRE-FRONTAL TROUGH...WHICH WILL SUPPORT INCREASING
SHRA COVERAGE THROUGH THE REMAINDER OF THE AFTERNOON AND INTO THE
EVENING.  MID LEVEL DYNAMICS ARE COMPLICATED WITH  SEVERAL WEAK VORT
MAXIMA INDICATED IN RADAR AND SATELLITE IMAGERY...WHICH WILL
COMPLICATE THE THUNDER FORECAST.  ANTICIPATE THAT CONVECTIVE WILL
REMAIN RELATIVELY SCATTERED WITH SOME SHORT LINES OR SMALL CLUSTERS
POSSIBLY DEVELOPING.  AS DEEP LAYER SHEAR REMAINS RELATIVELY
WEAK...DO NOT EXPECT STORMS TO REACH SEVERE LEVELS...BUT WITH PWATS
OF AROUND 1 INCH PER THE 12Z SOUNDINGS FROM ILX/DVN...OCCASIONAL
HEAVY DOWNPOURS ARE LIKELY AND SOME SMALL HAIL IS NOT OUT OF THE
QUESTION.

THE COLD FRONT SHOULD PUSH THROUGH THE ROCKFORD METRO AREA BY EARLY
EVENING AND THEN PUSH THROUGH THE CHICAGO METRO AREA  SHORTLY BEFORE
MIDNIGHT WHILE CLEARING THE FAR SERN PORTIONS OF THE CWA DURG THE
EARLY MORNING HOURS...AND ALL PCPN SHOULD MOVE OUT OF THE CWA DURG
THE PRE-DAWN HOURS.  COOLER...DRIER AIR WILL QUICKLY FILTER IN
BEHIND THE FRONT AS HIGH PRESSURE BUILDS ACROSS THE NORTHERN PLAINS
AND INTO THE MIDDLE AND UPPER MISSISSIPPI VALLEYS.  TEMPERATURES
WILL BE NEARLY 20 DEGREES LOWER THAN THOSE SEEN THIS AFTERNOON.
AFTER A FEW DAYS OF VERY PLEASANT WEATHER WITH HIGHS IN THE 70S TO
AROUND 80F...COLD ADVECTION UNDER DEEP LAYER NWLY FLOW WILL DROP
TEMPERATURES INTO THE UPPER 50S TO AROUND 60F FOR MUCH OF THE REGION
TOMORROW.  AS THE CENTER OF THE HIGH PRESSURE MOVES ACROSS WISCONSIN
TOMORROW...SFC WINDS WILL GRADUALLY VEER FROM NWLY...THROUGH NLY TO
ENELY BY TOMORROW AFTERNOON.  THIS WILL SET UP FLOW OFF OF THE
RELATIVELY COLD LAKE MICHIGAN WATERS AND THE ILLINOIS AND INDIANA
LAKE FRONTS...INCLUDING DOWNTOWN CHICAGO/WAUKEGAN/GARY WILL LIKELY
SEE HIGHS ONLY IN THE MIDDLE 40S.

FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...LATE TUESDAY
INTO WEDNESDAY...THE UPPER LEVEL PATTERN IS EXPECTED TO
BECOME MORE HIGHLY AMPLIFIED...WITH SLOWING EASTWARD PROGRESSION TO
THE UPPER LEVEL AND SFC PATTERN.  IN PARTICULAR...THE SFC HIGH IS
EXPECTED TO SLOWLY MOVE ACROSS THE CENTRAL GREAT LAKES REGION WITH
SFC RIDGING EXTENDING SOUTH INTO THE OHIO VALLEY.  THIS WILL KEEP
COOL CONDITIONS OVER THE REGION. WITH GENERALLY NORTHERLY SFC WINDS
IN PLACE...THE LAKEFRONT LOCATIONS WILL...AGAIN...BE SIGNIFICANTLY
COOLER THAN FARTHER INLAND...WITH HIGH WEDNESDAY REMAINING IN THE
MIDDLE 40S ALONG THE LAKE.  BY LATE WEDNESDAY AFTERNOON...THE SFC
RIDGE AXIS SHOULD MOVE EAST OF THE AREA AND A RETURN FLOW OR WARMER
AIR SHOULD BRING TO DEVELOP LATE IN THE DAY AND WITH SELY WINDS
SETTING UP IN THE AFTERNOON...INLAND LOCATIONS COULD REBOUND INTO
THE UPPER 50S TO LOWER 60S.

FOR THE LONGER TERM FORECAST PERIOD...THURSDAY THROUGH SUNDAY...THE
THE MODEL GUIDANCE IS SETTLING INTO MUCH BETTER AGREEMENT ON THE
LONG-WAVE PATTERN...AT LEAST INTO SATURDAY.  THE MODELS ARE
ADVERTISING THAT THE UPPER LEVEL PATTERN SHOULD REMAIN HIGHLY
AMPLIFIED...BUT STEADILY PROGRESSIVE.  BY THURSDAY...A NRN STREAM
PACIFIC SYSTEM WILL TOP AN UPPER RIDGE OVER THE ROCKIES AND MOVE OUT
INTO THE NRN PLAINS.  A MIDDLE STREAM SHORTWAVE IS EXPECTED TO MOVE
THROUGH THE FOUR CORNERS REGION AND INTO THE CENTRAL PLAINS.  THE
12Z RUNS OF THE GFS AND ECMWF BOTH SHOW SOME DEGREE OF PHASING OF THE
TWO SHORTWAVES...INTO A FULL LATITUDE OPEN TROUGH ALOFT AND A
COMPLEX SYSTEM AT THE SFC WITH A STRENGTHENING TRIPLE POINT LOW OVER
THE CENTRAL PLAINS WITH AN OCCLUSION TO A WEAKENING SFC LOW OVER THE
NRN PLAINS AND A STRONG COLD FRONT EXTENDING SWWD INTO TEXAS.  BY
THURSDAY AFTERNOON/EVENING...THE TRIPLE POINT LOW WILL BECOME THE
DOMINANT LOW...AND THE OCCLUSION EVOLVING INTO MORE OF AN INVERTED
TROUGH.  THE AIRMASS OUT AHEAD OF THE SYSTEM SHOULD BECOME
INCREASINGLY WARM/MOISTER/MORE UNSTABLE WITH LOW LEVEL FLOW OFF OF
AN OPEN GULF OF MEXICO.  GIVEN THE BETTER MODEL CONSENSUS FOR
THURSDAY INTO FRIDAY...WILL CARRY CATEGORICAL POPS WITH THE PASSAGE
OF THE SYSTEM.  THE MODEL GUIDANCE IS EVEN INDICATING SOME SURFACE
BASED INSTABILITY IN THE WARM SECTOR...LEADING HIGHER CONFIDENCE IN
THUNDERSTORM ACTIVITY AS WELL...WITH THE BEST CHANCE FOR
THUNDERSTORMS THURSDAY INTO THURSDAY EVENING.  THE 12Z GFS IS
INDICATING PWATS OF 1.0 TO 1.5 INCHES IN THE AIRMASS AHEAD OF THE
FRONT...SO HEAVY RAINFALL WILL ALSO BE A POSSIBILITY WITH THIS
SYSTEM.

WHILE THE MODELS ARE CONSISTENT IN PUSHING THE SYSTEM EAST  OF THE
AREA BY FRIDAY MORNING...THE MODEL SOLUTIONS BEGIN TO DIVERGE
SIGNIFICANTLY BY FRIDAY NIGHT AND SATURDAY...WITH THE GFS BECOMING
MUCH MORE AMPLIFIED WITH DEEPER TROUGHING OVER THE WEST AND EAST
COAST AND STRONGER RIDGING OVER THE CENTRAL CONUS.  THE GFS
CONTINUES THE TREND OF AMPLIFICATION THROUGH THE WEEKEND WITH CLOSED
UPPER LOWS DEVELOPING OVER THE SRN ROCKIES AND NEW ENGLAND AND A
VERY HIGH AMPLITUDE RIDGE OVER THE CNTRL CONUS.  THE ECMWF DEVELOPS
A SIMILAR...BUT WEAKER UPPER LOW OVER NEW ENGLAND AND ONLY AN OPEN
WAVE OVER THE WRN CONUS.  GIVEN THE LARGE UNCERTAINTY IN THE LATTER
PORTIONS OF THE LONG TERM FORECAST PERIOD...HAVE OPTED TO MAKE
LITTLE CHANGE TO THE GOING FORECAST.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SHRA WITH ISOLATED/SCATTERED TSRA THROUGH MID-EVE.
* CHANCE FOR A BRIEF PERIOD OF MVFR CIGS EARLY THIS EVE.
* WEST/SOUTHWEST WINDS THIS AFTERNOON BECOMING NORTHWEST BY
  EARLY-MID EVE
* WINDS BECOMING NORTHEAST TUESDAY AFTERNOON.

//DISCUSSION...UPDATED 18Z...

BROAD LOW PRESSURE ACROSS WI/U.P. OF MICHIGAN WILL CONSOLIDATE
GOING INTO THIS EVE AND STEER A COLD FRONT ACROSS THE AREA EARLY
THIS EVE. AHEAD OF THIS...FORCING AND MOISTURE WILL BE ENOUGH TO
CONTINUE AREAS OF SHOWERS. THERE LIKELY WILL BE AN UPTICK IN
COVERAGE DURING THE MID-LATE AFTERNOON ACROSS NORTHERN/CENTRAL
IL. HOW MUCH THUNDER IS EMBEDDED IN THAT REMAINS SOMEWHAT
UNCERTAIN...BUT IT LIKELY TO BE ON THE ORDER OF 30-50 PERCENT.
HAVE TRENDED TO A VCTS FOR THAT REASON. IN SOME OF THE MORE MODEST
SHOWERS NEAR THE FRONT THERE HAVE BEEN OBSERVATIONS OF BRIEF IFR
VISIBILITY TO THE WEST AND FEEL THAT COVERAGE OF AT LEAST SHOWERS
AHEAD OF THE FRONT WILL BE HIGH ENOUGH HERE TO MAINTAIN THAT 3SM
MENTION IN THE TAFS. MVFR CIGS ARE LESS COMMON SO HAVE NOT
INCLUDED IN TAFS. WITH FROPA THIS EVE WILL COME DRYING ALONG WITH
NORTHWEST GUSTS WHICH ARE FAVORED TO LAST INTO THE DAY TUESDAY.
GIVEN THE NNW TRAJECTORY OF SYNOPTIC SURFACE WINDS AND THE
DIMINISHING SPEEDS BY MIDDAY TUE...CLIMATOLOGY WILL LIKELY TAKE
OVER FOR A NORTHEAST WIND TO DEVELOP OFF THE LAKE AT ORD AND MDW.

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH IN SHRA OCCURRING AND WINDS REMAINING BETWEEN 190 AND 300
  THROUGH EARLY EVE INCLUDING UNDER AND NEAR SHRA.
* LOW IN TSRA OCCURRING AT THE AIRFIELDS THEMSELVES. HIGH IN
  TIMING IF THEY DO OCCUR BETWEEN BETWEEN 22Z-01Z.
* LOW IN WHETHER MVFR CIGS CAN DEVELOP.
* HIGH IN WIND SHIFT TO NORTHEAST TUESDAY AFTERNOON BUT LOW IN
  TIMING.

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MTF/RODRIGUEZ

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 PM MONDAY TO 3
     PM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 PM MONDAY TO 10
     AM TUESDAY.

&&

$$

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 211959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT MON APR 21 2014

.DISCUSSION...
1051 AM CDT

SOME HIGHER TEMPORAL RESOLUTION HAS BEEN MADE TO THE RAIN
LIKELIHOOD ALONG WITH THE CHANCES FOR THUNDER FOR THE REST OF
TODAY AND TONIGHT...BUT ALL IN ALL MAIN THEME OF THE FORECAST
CONTINUES. THERE WERE TEMPERATURE ADJUSTMENTS TO BUMP FORECAST
HIGHS DOWN SEVERAL DEGREES ACROSS MANY COMMUNITIES...ESPECIALLY
NORTH.

THE LONG WAVE TROUGH WITH TWO MAIN SHORT WAVE CENTERS IS MOVING
EASTWARD INTO THE MISSISSIPPI VALLEY LATE THIS MORNING. WHILE THE
TWO MAIN CENTERS WILL SPLIT THE FORECAST AREA...SEVERAL MINOR
IMPULSES EMBEDDED WITHIN THE TROUGH AND JUST OVERALL BROAD ASCENT
AND DEEPER MOISTURE CONTINUE TO HAVE RAIN ENCROACHING ON THE
AREA. ONE LEAD VORT CENTER NEAR ST LOUIS IS MOVING NORTHEAST AND
THIS WILL LIKELY CONTINUE TO SPREAD SHOWERS ACROSS CENTRAL IL AND
INTO THE SOUTHERN FORECAST AREA EARLY THIS AFTERNOON. THIS HAS
OUTPACED THE INSTABILITY SO NOT EXPECTING MUCH THUNDER WITH THAT.
THIS STILL MAY BE ENOUGH TO DROP TEMPERATURES IN SOUTHERN
LOCATIONS A COUPLE DEGREES AS WELL...BUT WITH TEMPERATURES ALREADY
AT OR ABOVE 70 AT SEVERAL SITES IN THE SOUTHERN CWA HAVE NOT
ADJUSTED FORECAST HIGHS AT THIS TIME. FOR THE NORTHERN FORECAST
AREA...THICKENING CLOUDS AND NEARBY SHOWER ACTIVITY HAVE ALREADY
STUNTED TEMPERATURES WITH FREEPORT AND STERLING HAVING HELD STEADY
IN THE PAST HOUR. HAVE LOWERED TEMPERATURES BY SEVERAL DEGREES
OVER NORTH CENTRAL IL AND THERE LIKELY WILL BE SOME FLUCTUATIONS
AS RAIN MOVES IN.

THE MAIN PRECIP COVERAGE AXIS AS WELL AS THUNDER CHANCES WILL COME
WITH THE DEEPER CONVERGENCE/FORCING AHEAD OF THE TROUGH AS IT
SHIFTS WEST-TO-EAST OVER THE AREA FROM MID AFTERNOON THROUGH MID-
EVE. IN GENERAL THAT WAS GOING IN THE FORECAST AND HAVE JUST
INCREASED MAGNITUDE OF POPS AND REFINED TIMING. A SOMEWHAT DIFFUSE
RIBBON OF INSTABILITY ASSOCIATED WITH MID-UPPER 50S LOW-LEVEL DEW
POINTS IS FAVORED TO SUPPORT ISOLATED TO SCATTERED EMBEDDED
THUNDER WITHIN THIS AXIS. PRECIP MAY LINGER AFTER FROPA A
BIT...BUT SHOULD BE EAST OF ROCKFORD BY SUNSET AND EAST OF CHICAGO
BY 10 PM OR SO.

MTF/KREIN

//PREV DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SHRA WITH ISOLATED/SCATTERED TSRA THROUGH MID-EVE.
* CHANCE FOR A BRIEF PERIOD OF MVFR CIGS EARLY THIS EVE.
* WEST/SOUTHWEST WINDS THIS AFTERNOON BECOMING NORTHWEST BY
  EARLY-MID EVE
* WINDS BECOMING NORTHEAST TUESDAY AFTERNOON.

//DISCUSSION...UPDATED 18Z...

BROAD LOW PRESSURE ACROSS WI/U.P. OF MICHIGAN WILL CONSOLIDATE
GOING INTO THIS EVE AND STEER A COLD FRONT ACROSS THE AREA EARLY
THIS EVE. AHEAD OF THIS...FORCING AND MOISTURE WILL BE ENOUGH TO
CONTINUE AREAS OF SHOWERS. THERE LIKELY WILL BE AN UPTICK IN
COVERAGE DURING THE MID-LATE AFTERNOON ACROSS NORTHERN/CENTRAL
IL. HOW MUCH THUNDER IS EMBEDDED IN THAT REMAINS SOMEWHAT
UNCERTAIN...BUT IT LIKELY TO BE ON THE ORDER OF 30-50 PERCENT.
HAVE TRENDED TO A VCTS FOR THAT REASON. IN SOME OF THE MORE MODEST
SHOWERS NEAR THE FRONT THERE HAVE BEEN OBSERVATIONS OF BRIEF IFR
VISIBILITY TO THE WEST AND FEEL THAT COVERAGE OF AT LEAST SHOWERS
AHEAD OF THE FRONT WILL BE HIGH ENOUGH HERE TO MAINTAIN THAT 3SM
MENTION IN THE TAFS. MVFR CIGS ARE LESS COMMON SO HAVE NOT
INCLUDED IN TAFS. WITH FROPA THIS EVE WILL COME DRYING ALONG WITH
NORTHWEST GUSTS WHICH ARE FAVORED TO LAST INTO THE DAY TUESDAY.
GIVEN THE NNW TRAJECTORY OF SYNOPTIC SURFACE WINDS AND THE
DIMINISHING SPEEDS BY MIDDAY TUE...CLIMATOLOGY WILL LIKELY TAKE
OVER FOR A NORTHEAST WIND TO DEVELOP OFF THE LAKE AT ORD AND MDW.

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH IN SHRA OCCURRING AND WINDS REMAINING BETWEEN 190 AND 300
  THROUGH EARLY EVE INCLUDING UNDER AND NEAR SHRA.
* LOW IN TSRA OCCURRING AT THE AIRFIELDS THEMSELVES. HIGH IN
  TIMING IF THEY DO OCCUR BETWEEN BETWEEN 22Z-01Z.
* LOW IN WHETHER MVFR CIGS CAN DEVELOP.
* HIGH IN WIND SHIFT TO NORTHEAST TUESDAY AFTERNOON BUT LOW IN
  TIMING.

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MTF/RODRIGUEZ

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

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

&&

$$

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 211956
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
256 PM CDT MON APR 21 2014

.DISCUSSION...
1051 AM CDT

SOME HIGHER TEMPORAL RESOLUTION HAS BEEN MADE TO THE RAIN
LIKELIHOOD ALONG WITH THE CHANCES FOR THUNDER FOR THE REST OF
TODAY AND TONIGHT...BUT ALL IN ALL MAIN THEME OF THE FORECAST
CONTINUES. THERE WERE TEMPERATURE ADJUSTMENTS TO BUMP FORECAST
HIGHS DOWN SEVERAL DEGREES ACROSS MANY COMMUNITIES...ESPECIALLY
NORTH.

THE LONG WAVE TROUGH WITH TWO MAIN SHORT WAVE CENTERS IS MOVING
EASTWARD INTO THE MISSISSIPPI VALLEY LATE THIS MORNING. WHILE THE
TWO MAIN CENTERS WILL SPLIT THE FORECAST AREA...SEVERAL MINOR
IMPULSES EMBEDDED WITHIN THE TROUGH AND JUST OVERALL BROAD ASCENT
AND DEEPER MOISTURE CONTINUE TO HAVE RAIN ENCROACHING ON THE
AREA. ONE LEAD VORT CENTER NEAR ST LOUIS IS MOVING NORTHEAST AND
THIS WILL LIKELY CONTINUE TO SPREAD SHOWERS ACROSS CENTRAL IL AND
INTO THE SOUTHERN FORECAST AREA EARLY THIS AFTERNOON. THIS HAS
OUTPACED THE INSTABILITY SO NOT EXPECTING MUCH THUNDER WITH THAT.
THIS STILL MAY BE ENOUGH TO DROP TEMPERATURES IN SOUTHERN
LOCATIONS A COUPLE DEGREES AS WELL...BUT WITH TEMPERATURES ALREADY
AT OR ABOVE 70 AT SEVERAL SITES IN THE SOUTHERN CWA HAVE NOT
ADJUSTED FORECAST HIGHS AT THIS TIME. FOR THE NORTHERN FORECAST
AREA...THICKENING CLOUDS AND NEARBY SHOWER ACTIVITY HAVE ALREADY
STUNTED TEMPERATURES WITH FREEPORT AND STERLING HAVING HELD STEADY
IN THE PAST HOUR. HAVE LOWERED TEMPERATURES BY SEVERAL DEGREES
OVER NORTH CENTRAL IL AND THERE LIKELY WILL BE SOME FLUCTUATIONS
AS RAIN MOVES IN.

THE MAIN PRECIP COVERAGE AXIS AS WELL AS THUNDER CHANCES WILL COME
WITH THE DEEPER CONVERGENCE/FORCING AHEAD OF THE TROUGH AS IT
SHIFTS WEST-TO-EAST OVER THE AREA FROM MID AFTERNOON THROUGH MID-
EVE. IN GENERAL THAT WAS GOING IN THE FORECAST AND HAVE JUST
INCREASED MAGNITUDE OF POPS AND REFINED TIMING. A SOMEWHAT DIFFUSE
RIBBON OF INSTABILITY ASSOCIATED WITH MID-UPPER 50S LOW-LEVEL DEW
POINTS IS FAVORED TO SUPPORT ISOLATED TO SCATTERED EMBEDDED
THUNDER WITHIN THIS AXIS. PRECIP MAY LINGER AFTER FROPA A
BIT...BUT SHOULD BE EAST OF ROCKFORD BY SUNSET AND EAST OF CHICAGO
BY 10 PM OR SO.

MTF/KREIN

//PREV DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* SHRA WITH ISOLATED/SCATTERED TSRA DURING THE MID-AFTERNOON
  THROUGH MID-EVE.
* CHANCE FOR A BRIEF PERIOD OF MVFR CIGS EARLY THIS EVE.
* SOUTHWEST TO NORTHWEST WINDS THIS AFTERNOON BECOMING NORTHWEST
  BY EARLY-MID EVE
* WINDS BECOMING NORTHEAST TUESDAY AFTERNOON.

//DISCUSSION...UPDATED 18Z...

BROAD LOW PRESSURE ACROSS WI/U.P. OF MICHIGAN WILL CONSOLIDATE
GOING INTO THIS EVE AND STEER A COLD FRONT ACROSS THE AREA EARLY
THIS EVE. AHEAD OF THIS...FORCING AND MOISTURE WILL BE ENOUGH TO
CONTINUE AREAS OF SHOWERS. THERE LIKELY WILL BE AN UPTICK IN
COVERAGE DURING THE MID-LATE AFTERNOON ACROSS NORTHERN/CENTRAL
IL. HOW MUCH THUNDER IS EMBEDDED IN THAT REMAINS SOMEWHAT
UNCERTAIN...BUT IT LIKELY TO BE ON THE ORDER OF 30-50 PERCENT.
HAVE TRENDED TO A VCTS FOR THAT REASON. IN SOME OF THE MORE MODEST
SHOWERS NEAR THE FRONT THERE HAVE BEEN OBSERVATIONS OF BRIEF IFR
VISIBILITY TO THE WEST AND FEEL THAT COVERAGE OF AT LEAST SHOWERS
AHEAD OF THE FRONT WILL BE HIGH ENOUGH HERE TO MAINTAIN THAT 3SM
MENTION IN THE TAFS. MVFR CIGS ARE LESS COMMON SO HAVE NOT
INCLUDED IN TAFS. WITH FROPA THIS EVE WILL COME DRYING ALONG WITH
NORTHWEST GUSTS WHICH ARE FAVORED TO LAST INTO THE DAY TUESDAY.
GIVEN THE NNW TRAJECTORY OF SYNOPTIC SURFACE WINDS AND THE
DIMINISHING SPEEDS BY MIDDAY TUE...CLIMATOLOGY WILL LIKELY TAKE
OVER FOR A NORTHEAST WIND TO DEVELOP OFF THE LAKE AT ORD AND MDW.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH IN SHRA OCCURRING AND WINDS REMAINING BETWEEN 190 AND 320
  THIS AFTERNOON AND EARLY EVE INCLUDING UNDER AND NEAR SHRA.
* LOW IN TSRA OCCURRING. MEDIUM THAT IF THEY DO OCCUR IT WOULD BE
  BETWEEN 22Z-01Z.
* LOW IN WHETHER MVFR CIGS CAN DEVELOP.
* HIGH IN WIND SHIFT TO NORTHEAST TUESDAY AFTERNOON BUT LOW IN
  TIMING.

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MTF/RODRIGUEZ

&&

.MARINE...
253 PM CDT

A BROAD LOW PRESSURE SYSTEM WILL MOVE ACROSS THE GREAT LAKES THIS
EVENING AND TONIGHT DRAGGING A COLD FRONT DOWN LAKE MICHIGAN FROM
MID TO LATE THIS EVENING. NNW WINDS WILL PICK UP BEHIND THE FRONT
WITH A WINDOW OF 30 KT GUSTS POSSIBLE. A SMALL CRAFT ADVISORY
REMAINS IN EFFECT FROM MID EVENING THROUGH TOMORROW MORNING THOUGH
WILL BE PARTICULARLY MARGINAL FOR THE ILLINOIS SHORES. EXTENDED
THE ADVISORY INTO THE AFTERNOON FOR INDIANA THOUGH WHICH WILL HAVE
HIGHER WAVES FOR A FEW MORE HOURS INTO THE AFTERNOON. HIGH
PRESSURE WILL ALLOW WINDS TO DIMINISH SOME TUESDAY ALLOWING LAKE
BREEZES TO DEVELOP...ESPECIALLY ON THE WESTERN SIDE OF THE LAKE
WHERE THE GRADIENT IS MORE RELAXED. THE HIGH WILL MOVE OVERHEAD
WEDNESDAY WITH WINDS BECOMING LIGHT AND VARIABLE FOR A
PERIOD...AND AGAIN ALLOWING LAKE BREEZES TO DEVELOP IN THE
AFTERNOON. SOUTHEASTERLY FLOW BEGINS TO RAMP UP WEDNESDAY NIGHT
INTO THURSDAY AS LOW PRESSURE TAKES SHAPE OVER THE CENTRAL PLAINS
AND LIFTS INTO THE UPPER MIDWEST. SOUTHEAST SUSTAINED WINDS TO
AROUND 25 KT ARE EXPECTED...THOUGH GUSTS SHOULD STAY IN CHECK AS A
STABLE MARINE LAYER DEVELOPS. BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 PM MONDAY TO 3
     PM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 PM MONDAY TO 10
     AM TUESDAY.

&&

$$

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 211737
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1237 PM CDT MON APR 21 2014

.DISCUSSION...
1051 AM CDT

SOME HIGHER TEMPORAL RESOLUTION HAS BEEN MADE TO THE RAIN
LIKELIHOOD ALONG WITH THE CHANCES FOR THUNDER FOR THE REST OF
TODAY AND TONIGHT...BUT ALL IN ALL MAIN THEME OF THE FORECAST
CONTINUES. THERE WERE TEMPERATURE ADJUSTMENTS TO BUMP FORECAST
HIGHS DOWN SEVERAL DEGREES ACROSS MANY COMMUNITIES...ESPECIALLY
NORTH.

THE LONG WAVE TROUGH WITH TWO MAIN SHORT WAVE CENTERS IS MOVING
EASTWARD INTO THE MISSISSIPPI VALLEY LATE THIS MORNING. WHILE THE
TWO MAIN CENTERS WILL SPLIT THE FORECAST AREA...SEVERAL MINOR
IMPULSES EMBEDDED WITHIN THE TROUGH AND JUST OVERALL BROAD ASCENT
AND DEEPER MOISTURE CONTINUE TO HAVE RAIN ENCROACHING ON THE
AREA. ONE LEAD VORT CENTER NEAR ST LOUIS IS MOVING NORTHEAST AND
THIS WILL LIKELY CONTINUE TO SPREAD SHOWERS ACROSS CENTRAL IL AND
INTO THE SOUTHERN FORECAST AREA EARLY THIS AFTERNOON. THIS HAS
OUTPACED THE INSTABILITY SO NOT EXPECTING MUCH THUNDER WITH THAT.
THIS STILL MAY BE ENOUGH TO DROP TEMPERATURES IN SOUTHERN
LOCATIONS A COUPLE DEGREES AS WELL...BUT WITH TEMPERATURES ALREADY
AT OR ABOVE 70 AT SEVERAL SITES IN THE SOUTHERN CWA HAVE NOT
ADJUSTED FORECAST HIGHS AT THIS TIME. FOR THE NORTHERN FORECAST
AREA...THICKENING CLOUDS AND NEARBY SHOWER ACTIVITY HAVE ALREADY
STUNTED TEMPERATURES WITH FREEPORT AND STERLING HAVING HELD STEADY
IN THE PAST HOUR. HAVE LOWERED TEMPERATURES BY SEVERAL DEGREES
OVER NORTH CENTRAL IL AND THERE LIKELY WILL BE SOME FLUCTUATIONS
AS RAIN MOVES IN.

THE MAIN PRECIP COVERAGE AXIS AS WELL AS THUNDER CHANCES WILL COME
WITH THE DEEPER CONVERGENCE/FORCING AHEAD OF THE TROUGH AS IT
SHIFTS WEST-TO-EAST OVER THE AREA FROM MID AFTERNOON THROUGH MID-
EVE. IN GENERAL THAT WAS GOING IN THE FORECAST AND HAVE JUST
INCREASED MAGNITUDE OF POPS AND REFINED TIMING. A SOMEWHAT DIFFUSE
RIBBON OF INSTABILITY ASSOCIATED WITH MID-UPPER 50S LOW-LEVEL DEW
POINTS IS FAVORED TO SUPPORT ISOLATED TO SCATTERED EMBEDDED
THUNDER WITHIN THIS AXIS. PRECIP MAY LINGER AFTER FROPA A
BIT...BUT SHOULD BE EAST OF ROCKFORD BY SUNSET AND EAST OF CHICAGO
BY 10 PM OR SO.

MTF/KREIN

//PREV DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* SHRA WITH ISOLATED/SCATTERED TSRA DURING THE MID-AFTERNOON
  THROUGH MID-EVE.
* CHANCE FOR A BRIEF PERIOD OF MVFR CIGS EARLY THIS EVE.
* SOUTHWEST TO NORTHWEST WINDS THIS AFTERNOON BECOMING NORTHWEST
  BY EARLY-MID EVE
* WINDS BECOMING NORTHEAST TUESDAY AFTERNOON.


//DISCUSSION...UPDATED 18Z...

BROAD LOW PRESSURE ACROSS WI/U.P. OF MICHIGAN WILL CONSOLIDATE
GOING INTO THIS EVE AND STEER A COLD FRONT ACROSS THE AREA EARLY
THIS EVE. AHEAD OF THIS...FORCING AND MOISTURE WILL BE ENOUGH TO
CONTINUE AREAS OF SHOWERS. THERE LIKELY WILL BE AN UPTICK IN
COVERAGE DURING THE MID-LATE AFTERNOON ACROSS NORTHERN/CENTRAL
IL. HOW MUCH THUNDER IS EMBEDDED IN THAT REMAINS SOMEWHAT
UNCERTAIN...BUT IT LIKELY TO BE ON THE ORDER OF 30-50 PERCENT.
HAVE TRENDED TO A VCTS FOR THAT REASON. IN SOME OF THE MORE MODEST
SHOWERS NEAR THE FRONT THERE HAVE BEEN OBSERVATIONS OF BRIEF IFR
VISIBILITY TO THE WEST AND FEEL THAT COVERAGE OF AT LEAST SHOWERS
AHEAD OF THE FRONT WILL BE HIGH ENOUGH HERE TO MAINTAIN THAT 3SM
MENTION IN THE TAFS. MVFR CIGS ARE LESS COMMON SO HAVE NOT
INCLUDED IN TAFS. WITH FROPA THIS EVE WILL COME DRYING ALONG WITH
NORTHWEST GUSTS WHICH ARE FAVORED TO LAST INTO THE DAY TUESDAY.
GIVEN THE NNW TRAJECTORY OF SYNOPTIC SURFACE WINDS AND THE
DIMINISHING SPEEDS BY MIDDAY TUE...CLIMATOLOGY WILL LIKELY TAKE
OVER FOR A NORTHEAST WIND TO DEVELOP OFF THE LAKE AT ORD AND MDW.


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH IN SHRA OCCURRING AND WINDS REMAINING BETWEEN 190 AND 320
  THIS AFTERNOON AND EARLY EVE INCLUDING UNDER AND NEAR SHRA.
* LOW IN TSRA OCCURRING. MEDIUM THAT IF THEY DO OCCUR IT WOULD BE
  BETWEEN 22Z-01Z.
* LOW IN WHETHER MVFR CIGS CAN DEVELOP.
* HIGH IN WIND SHIFT TO NORTHEAST TUESDAY AFTERNOON BUT LOW IN
  TIMING.


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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MTF/RODRIGUEZ

&&

.MARINE...
433 AM CDT

AS A RIDGE OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES CONTINUES
TO SHIFT TO THE EAST THIS MORNING...A TROUGH OF LOW PRESSURE OVER
THE CENTRAL AND NORTHERN PLAINS WILL SHIFT EAST TO THE CENTRAL
GREAT LAKES TODAY. WITH THESE FEATURES IN PLACE...EXPECT GENERALLY
SOUTHERLY FLOW ACROSS THE LAKE FOR MOST OF TODAY. ALTHOUGH...THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT WILL SLOWLY APPROACH THE
LAKE LATER IN THE DAY AND EVENING...WITH WINDS TURNING TO THE
SOUTHWEST AND WEST BEFORE TURNING TO THE NORTHWEST ON THE BACKSIDE
OF THIS FRONT. WINDS WILL RAMP UP QUICKLY BEHIND THE FRONT WITH TO
30 KT WINDS EXPECTED TONIGHT AND INTO TUESDAY MORNING. THEN AS
THIS LOW DEPARTS AND HIGH PRESSURE BEGINS SHIFTING TOWARDS THE
LAKE TUESDAY...WINDS WILL DIMINISH THROUGHOUT THE DAY. A PERIOD OF
LIGHTER FLOW OVER THE LAKE IS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY AS THIS HIGH BUILDS OVERHEAD. EXPECT THE NEXT SYSTEM TO
AFFECT THE REGION TO BEGIN SHIFTING EAST TOWARDS THE LAKE
WEDNESDAY NIGHT INTO THURSDAY...WITH SOUTHEAST WINDS INCREASING
DURING THIS PERIOD.

RODRIGUEZ

&&

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

&&

$$

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 211551
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1051 AM CDT MON APR 21 2014

.DISCUSSION...
1051 AM CDT

SOME HIGHER TEMPORAL RESOLUTION HAS BEEN MADE TO THE RAIN
LIKELIHOOD ALONG WITH THE CHANCES FOR THUNDER FOR THE REST OF
TODAY AND TONIGHT...BUT ALL IN ALL MAIN THEME OF THE FORECAST
CONTINUES. THERE WERE TEMPERATURE ADJUSTMENTS TO BUMP FORECAST
HIGHS DOWN SEVERAL DEGREES ACROSS MANY COMMUNITIES...ESPECIALLY
NORTH.

THE LONG WAVE TROUGH WITH TWO MAIN SHORT WAVE CENTERS IS MOVING
EASTWARD INTO THE MISSISSIPPI VALLEY LATE THIS MORNING. WHILE THE
TWO MAIN CENTERS WILL SPLIT THE FORECAST AREA...SEVERAL MINOR
IMPULSES EMBEDDED WITHIN THE TROUGH AND JUST OVERALL BROAD ASCENT
AND DEEPER MOISTURE CONTINUE TO HAVE RAIN ENCROACHING ON THE
AREA. ONE LEAD VORT CENTER NEAR ST LOUIS IS MOVING NORTHEAST AND
THIS WILL LIKELY CONTINUE TO SPREAD SHOWERS ACROSS CENTRAL IL AND
INTO THE SOUTHERN FORECAST AREA EARLY THIS AFTERNOON. THIS HAS
OUTPACED THE INSTABILITY SO NOT EXPECTING MUCH THUNDER WITH THAT.
THIS STILL MAY BE ENOUGH TO DROP TEMPERATURES IN SOUTHERN
LOCATIONS A COUPLE DEGREES AS WELL...BUT WITH TEMPERATURES ALREADY
AT OR ABOVE 70 AT SEVERAL SITES IN THE SOUTHERN CWA HAVE NOT
ADJUSTED FORECAST HIGHS AT THIS TIME. FOR THE NORTHERN FORECAST
AREA...THICKENING CLOUDS AND NEARBY SHOWER ACTIVITY HAVE ALREADY
STUNTED TEMPERATURES WITH FREEPORT AND STERLING HAVING HELD STEADY
IN THE PAST HOUR. HAVE LOWERED TEMPERATURES BY SEVERAL DEGREES
OVER NORTH CENTRAL IL AND THERE LIKELY WILL BE SOME FLUCTUATIONS
AS RAIN MOVES IN.

THE MAIN PRECIP COVERAGE AXIS AS WELL AS THUNDER CHANCES WILL COME
WITH THE DEEPER CONVERGENCE/FORCING AHEAD OF THE TROUGH AS IT
SHIFTS WEST-TO-EAST OVER THE AREA FROM MID AFTERNOON THROUGH MID-
EVE. IN GENERAL THAT WAS GOING IN THE FORECAST AND HAVE JUST
INCREASED MAGNITUDE OF POPS AND REFINED TIMING. A SOMEWHAT DIFFUSE
RIBBON OF INSTABILITY ASSOCIATED WITH MID-UPPER 50S LOW-LEVEL DEW
POINTS IS FAVORED TO SUPPORT ISOLATED TO SCATTERED EMBEDDED
THUNDER WITHIN THIS AXIS. PRECIP MAY LINGER AFTER FROPA A
BIT...BUT SHOULD BE EAST OF ROCKFORD BY SUNSET AND EAST OF CHICAGO
BY 10 PM OR SO.

MTF/KREIN

&&

.PREV DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* SHRA WITH SCATTERED TSRA MID-AFTERNOON THROUGH MID-EVE.
* CHANCE FOR MVFR CIGS EARLY THIS EVE.
* FROPA EARLY TO MID EVE.

MTF/RODRIGUEZ

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

RELATIVELY LIGHTER SOUTH TO SOUTHWEST WINDS IN PLACE THIS MORNING
AS SURFACE TROUGH REMAINS WELL WEST OF THE TERMINALS...AS MID/HIGH
LEVEL CLOUD COVER CONTINUE TO MOVE OVERHEAD. A TREND TOWARDS A
MORE SOUTHWEST TO WEST DIRECTION WILL OCCUR TODAY OUT AHEAD OF
THIS APPROACHING TROUGH AND FRONTAL BOUNDARY...WITH VFR CEILINGS
SLOWLY LOWERING. THIS MORNING WILL REMAIN DRY WITH LATEST RADAR
IMAGERY DEPICTING WIDELY SCATTERED SHOWERS/THUNDERSTORMS STILL
WELL WEST IN IOWA. ALTHOUGH...EXPECT SCATTERED SHOWERS TO BEGIN
MOVING ACROSS THE TERMINALS BY EARLY AFTERNOON WITH THIS
DEVELOPMENT PERSISTING INTO THE AFTERNOON. IT STILL APPEARS AS IF
MORE WIDESPREAD SHOWERS AND THUNDERSTORMS WILL BE TIED CLOSER TO
THE FRONT...AFFECTING THE TERMINALS DURING THE MID TO LATE
AFTERNOON TIME FRAME POSSIBLY LINGERING INTO THE EARLY EVENING.
EXPECT FROPA BY THIS EVENING...WITH WINDS TURNING TO THE NORTHWEST
WHILE PRECIP AND CLOUD COVER SHIFT TO THE SOUTHEAST.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH IN SHRA OCCURRING...MEDIUM IN TSRA OCCURRING. LOW/MEDIUM IN
  TIMING.
* LOW IN WEATHER MVFR CIGS CAN DEVELOP.
* MEDIUM IN WIND SHIFT TIMING TO NORTHWEST.

MTF/RODRIGUEZ

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
433 AM CDT

AS A RIDGE OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES CONTINUES
TO SHIFT TO THE EAST THIS MORNING...A TROUGH OF LOW PRESSURE OVER
THE CENTRAL AND NORTHERN PLAINS WILL SHIFT EAST TO THE CENTRAL
GREAT LAKES TODAY. WITH THESE FEATURES IN PLACE...EXPECT GENERALLY
SOUTHERLY FLOW ACROSS THE LAKE FOR MOST OF TODAY. ALTHOUGH...THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT WILL SLOWLY APPROACH THE
LAKE LATER IN THE DAY AND EVENING...WITH WINDS TURNING TO THE
SOUTHWEST AND WEST BEFORE TURNING TO THE NORTHWEST ON THE BACKSIDE
OF THIS FRONT. WINDS WILL RAMP UP QUICKLY BEHIND THE FRONT WITH TO
30 KT WINDS EXPECTED TONIGHT AND INTO TUESDAY MORNING. THEN AS
THIS LOW DEPARTS AND HIGH PRESSURE BEGINS SHIFTING TOWARDS THE
LAKE TUESDAY...WINDS WILL DIMINISH THROUGHOUT THE DAY. A PERIOD OF
LIGHTER FLOW OVER THE LAKE IS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY AS THIS HIGH BUILDS OVERHEAD. EXPECT THE NEXT SYSTEM TO
AFFECT THE REGION TO BEGIN SHIFTING EAST TOWARDS THE LAKE
WEDNESDAY NIGHT INTO THURSDAY...WITH SOUTHEAST WINDS INCREASING
DURING THIS PERIOD.

RODRIGUEZ

&&

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

&&

$$

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 211402
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
902 AM CDT MON APR 21 2014

.DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* SHRA WITH SCATTERED TSRA MID-AFTERNOON THROUGH MID-EVE.
* FROPA EARLY TO MID EVE.

MTF/RODRIGUEZ

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

RELATIVELY LIGHTER SOUTH TO SOUTHWEST WINDS IN PLACE THIS MORNING
AS SURFACE TROUGH REMAINS WELL WEST OF THE TERMINALS...AS MID/HIGH
LEVEL CLOUD COVER CONTINUE TO MOVE OVERHEAD. A TREND TOWARDS A
MORE SOUTHWEST TO WEST DIRECTION WILL OCCUR TODAY OUT AHEAD OF
THIS APPROACHING TROUGH AND FRONTAL BOUNDARY...WITH VFR CEILINGS
SLOWLY LOWERING. THIS MORNING WILL REMAIN DRY WITH LATEST RADAR
IMAGERY DEPICTING WIDELY SCATTERED SHOWERS/THUNDERSTORMS STILL
WELL WEST IN IOWA. ALTHOUGH...EXPECT SCATTERED SHOWERS TO BEGIN
MOVING ACROSS THE TERMINALS BY EARLY AFTERNOON WITH THIS
DEVELOPMENT PERSISTING INTO THE AFTERNOON. IT STILL APPEARS AS IF
MORE WIDESPREAD SHOWERS AND THUNDERSTORMS WILL BE TIED CLOSER TO
THE FRONT...AFFECTING THE TERMINALS DURING THE MID TO LATE
AFTERNOON TIME FRAME POSSIBLY LINGERING INTO THE EARLY EVENING.
EXPECT FROPA BY THIS EVENING...WITH WINDS TURNING TO THE NORTHWEST
WHILE PRECIP AND CLOUD COVER SHIFT TO THE SOUTHEAST.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN SHRA OCCURRING...MEDIUM IN TSRA OCCURRING. LOW/MEDIUM IN
  TIMING. MAY END UP BEING MORE OF 22Z-01Z FOR ORD LIKE MDW.
* MEDIUM IN WIND SHIFT TIMING TO NORTHWEST.

MTF/RODRIGUEZ

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
433 AM CDT

AS A RIDGE OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES CONTINUES
TO SHIFT TO THE EAST THIS MORNING...A TROUGH OF LOW PRESSURE OVER
THE CENTRAL AND NORTHERN PLAINS WILL SHIFT EAST TO THE CENTRAL
GREAT LAKES TODAY. WITH THESE FEATURES IN PLACE...EXPECT GENERALLY
SOUTHERLY FLOW ACROSS THE LAKE FOR MOST OF TODAY. ALTHOUGH...THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT WILL SLOWLY APPROACH THE
LAKE LATER IN THE DAY AND EVENING...WITH WINDS TURNING TO THE
SOUTHWEST AND WEST BEFORE TURNING TO THE NORTHWEST ON THE BACKSIDE
OF THIS FRONT. WINDS WILL RAMP UP QUICKLY BEHIND THE FRONT WITH TO
30 KT WINDS EXPECTED TONIGHT AND INTO TUESDAY MORNING. THEN AS
THIS LOW DEPARTS AND HIGH PRESSURE BEGINS SHIFTING TOWARDS THE
LAKE TUESDAY...WINDS WILL DIMINISH THROUGHOUT THE DAY. A PERIOD OF
LIGHTER FLOW OVER THE LAKE IS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY AS THIS HIGH BUILDS OVERHEAD. EXPECT THE NEXT SYSTEM TO
AFFECT THE REGION TO BEGIN SHIFTING EAST TOWARDS THE LAKE
WEDNESDAY NIGHT INTO THURSDAY...WITH SOUTHEAST WINDS INCREASING
DURING THIS PERIOD.

RODRIGUEZ

&&

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

&&

$$

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 211157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
657 AM CDT MON APR 21 2014

.DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

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

* FROPA THIS EVENING.

* SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING THIS AFTERNOON.

RODRIGUEZ

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

RELATIVELY LIGHTER SOUTH TO SOUTHWEST WINDS IN PLACE THIS MORNING
AS SURFACE TROUGH REMAINS WELL WEST OF THE TERMINALS...AS MID/HIGH
LEVEL CLOUD COVER CONTINUE TO MOVE OVERHEAD. A TREND TOWARDS A
MORE SOUTHWEST TO WEST DIRECTION WILL OCCUR TODAY OUT AHEAD OF
THIS APPROACHING TROUGH AND FRONTAL BOUNDARY...WITH VFR CEILINGS
SLOWLY LOWERING. THIS MORNING WILL REMAIN DRY WITH LATEST RADAR
IMAGERY DEPICTING WIDELY SCATTERED SHOWERS/THUNDERSTORMS STILL
WELL WEST IN IOWA. ALTHOUGH...EXPECT SCATTERED SHOWERS TO BEGIN
MOVING ACROSS THE TERMINALS BY EARLY AFTERNOON WITH THIS
DEVELOPMENT PERSISTING INTO THE AFTERNOON. IT STILL APPEARS AS IF
MORE WIDESPREAD SHOWERS AND THUNDERSTORMS WILL BE TIED CLOSER TO
THE FRONT...AFFECTING THE TERMINALS DURING THE MID TO LATE
AFTERNOON TIME FRAME POSSIBLY LINGERING INTO THE EARLY EVENING.
EXPECT FROPA BY THIS EVENING...WITH WINDS TURNING TO THE NORTHWEST
WHILE PRECIP AND CLOUD COVER SHIFT TO THE SOUTHEAST.

RODRIGUEZ


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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM HIGH CONFIDENCE WITH SHOWER/THUNDERSTORM
  POTENTIAL...MEDIUM CONFIDENCE OF TIMING/DURATION.

RODRIGUEZ

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...A PERIOD OF SHRA/TSRA LIKELY.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
433 AM CDT

AS A RIDGE OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES CONTINUES
TO SHIFT TO THE EAST THIS MORNING...A TROUGH OF LOW PRESSURE OVER
THE CENTRAL AND NORTHERN PLAINS WILL SHIFT EAST TO THE CENTRAL
GREAT LAKES TODAY. WITH THESE FEATURES IN PLACE...EXPECT GENERALLY
SOUTHERLY FLOW ACROSS THE LAKE FOR MOST OF TODAY. ALTHOUGH...THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT WILL SLOWLY APPROACH THE
LAKE LATER IN THE DAY AND EVENING...WITH WINDS TURNING TO THE
SOUTHWEST AND WEST BEFORE TURNING TO THE NORTHWEST ON THE BACKSIDE
OF THIS FRONT. WINDS WILL RAMP UP QUICKLY BEHIND THE FRONT WITH TO
30 KT WINDS EXPECTED TONIGHT AND INTO TUESDAY MORNING. THEN AS
THIS LOW DEPARTS AND HIGH PRESSURE BEGINS SHIFTING TOWARDS THE
LAKE TUESDAY...WINDS WILL DIMINISH THROUGHOUT THE DAY. A PERIOD OF
LIGHTER FLOW OVER THE LAKE IS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY AS THIS HIGH BUILDS OVERHEAD. EXPECT THE NEXT SYSTEM TO
AFFECT THE REGION TO BEGIN SHIFTING EAST TOWARDS THE LAKE
WEDNESDAY NIGHT INTO THURSDAY...WITH SOUTHEAST WINDS INCREASING
DURING THIS PERIOD.

RODRIGUEZ

&&

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

&&

$$

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 210934
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
434 AM CDT MON APR 21 2014

.DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

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

* SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING THIS AFTERNOON.

RODRIGUEZ

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

QUIET CONDITIONS TONIGHT/EARLY MONDAY MORNING...WITH MID/HIGH
LEVEL CLOUD COVER CONTINUING TO STREAM OVERHEAD AND SOUTH TO
SOUTHWEST WINDS REMAINING IN PLACE. EXPECT WINDS TO BECOME MORE
SOUTHWEST BY MID MORNING MONDAY WHILE SPEEDS INCREASE THROUGH MID
DAY AND THE AFTERNOON. EXPECT CLOUD COVER TO INCREASE WITH VFR
CEILINGS LIKELY BY MID DAY...AS SCATTERED SHOWERS BEGIN MOVING
ACROSS THE TERMINALS. THIS SCATTERED DEVELOPMENT WILL LIKELY
PERSIST IN THE AFTERNOON UNTIL BETTER DEVELOPMENT ARRIVES OUT
AHEAD OF APPROACHING FRONT LATE IN THE AFTERNOON AND EARLY
EVENING. ITS DURING THIS TIME THAT BEST THUNDER POTENTIAL WILL BE
BEFORE PRECIP QUICKLY EXITS TO THE EAST WITH FROPA...AND WITH
SOUTHWEST TO WEST WINDS TURNING TO THE NORTHWEST.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM HIGH CONFIDENCE WITH SHOWER/THUNDERSTORM
  POTENTIAL...MEDIUM CONFIDENCE OF TIMING/DURATION.

RODRIGUEZ

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
433 AM CDT

AS A RIDGE OF HIGH PRESSURE OVER THE EASTERN GREAT LAKES CONTINUES
TO SHIFT TO THE EAST THIS MORNING...A TROUGH OF LOW PRESSURE OVER
THE CENTRAL AND NORTHERN PLAINS WILL SHIFT EAST TO THE CENTRAL
GREAT LAKES TODAY. WITH THESE FEATURES IN PLACE...EXPECT GENERALLY
SOUTHERLY FLOW ACROSS THE LAKE FOR MOST OF TODAY. ALTHOUGH...THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT WILL SLOWLY APPROACH THE
LAKE LATER IN THE DAY AND EVENING...WITH WINDS TURNING TO THE
SOUTHWEST AND WEST BEFORE TURNING TO THE NORTHWEST ON THE BACKSIDE
OF THIS FRONT. WINDS WILL RAMP UP QUICKLY BEHIND THE FRONT WITH TO
30 KT WINDS EXPECTED TONIGHT AND INTO TUESDAY MORNING. THEN AS
THIS LOW DEPARTS AND HIGH PRESSURE BEGINS SHIFTING TOWARDS THE
LAKE TUESDAY...WINDS WILL DIMINISH THROUGHOUT THE DAY. A PERIOD OF
LIGHTER FLOW OVER THE LAKE IS EXPECTED TUESDAY NIGHT INTO
WEDNESDAY AS THIS HIGH BUILDS OVERHEAD. EXPECT THE NEXT SYSTEM TO
AFFECT THE REGION TO BEGIN SHIFTING EAST TOWARDS THE LAKE
WEDNESDAY NIGHT INTO THURSDAY...WITH SOUTHEAST WINDS INCREASING
DURING THIS PERIOD.

RODRIGUEZ

&&

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

&&

$$

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 210901
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 AM CDT MON APR 21 2014

.DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

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

* SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING THIS AFTERNOON.

RODRIGUEZ

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

QUIET CONDITIONS TONIGHT/EARLY MONDAY MORNING...WITH MID/HIGH
LEVEL CLOUD COVER CONTINUING TO STREAM OVERHEAD AND SOUTH TO
SOUTHWEST WINDS REMAINING IN PLACE. EXPECT WINDS TO BECOME MORE
SOUTHWEST BY MID MORNING MONDAY WHILE SPEEDS INCREASE THROUGH MID
DAY AND THE AFTERNOON. EXPECT CLOUD COVER TO INCREASE WITH VFR
CEILINGS LIKELY BY MID DAY...AS SCATTERED SHOWERS BEGIN MOVING
ACROSS THE TERMINALS. THIS SCATTERED DEVELOPMENT WILL LIKELY
PERSIST IN THE AFTERNOON UNTIL BETTER DEVELOPMENT ARRIVES OUT
AHEAD OF APPROACHING FRONT LATE IN THE AFTERNOON AND EARLY
EVENING. ITS DURING THIS TIME THAT BEST THUNDER POTENTIAL WILL BE
BEFORE PRECIP QUICKLY EXITS TO THE EAST WITH FROPA...AND WITH
SOUTHWEST TO WEST WINDS TURNING TO THE NORTHWEST.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM HIGH CONFIDENCE WITH SHOWER/THUNDERSTORM
  POTENTIAL...MEDIUM CONFIDENCE OF TIMING/DURATION.

RODRIGUEZ

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
125 PM CDT

LOW PRESSURE TRACKING ACROSS NORTHERN ONTARIO...WILL PUSH A
FRONTAL BOUNDARY ACROSS THE NORTHERN PORTION OF THE LAKE TONIGHT
INTO MONDAY. THIS WILL SET UP A PERIOD OF LIGHT AND VARIABLE
WINDS THERE THROUGH MONDAY. A SECOND AREA OF LOW PRESSURE WILL
MOVE ALONG THIS FRONT LATE MONDAY...AND ONCE THIS LOW MOVES EAST
OF THE LAKE...A PERIOD OF STRONGER NORTHERLY WINDS WILL SET UP
ACROSS THE LAKE MONDAY NIGHT INTO TUESDAY...BEFORE HIGH PRESSURE
BUILDS OVER THE LAKE WEDNESDAY NIGHT. THESE STRONGER NORTHERLY
WINDS COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS WITH HIGH
WAVES INTO THE NEAR SHORE WATERS FOR TUESDAY.

THE LATER PORTION OF THE WEEK APPEARS TO REMAIN ACTIVE
ACROSS THE GREAT LAKES REGION. IT APPEARS THAT ANOTHER SIGNIFICANT
AREA OF LOW PRESSURE WILL IMPACT THE UPPER MIDWEST AND THE GREAT
LAKES REGION LATE IN THE WEEK AND INTO EARLY NEXT WEEKEND. THIS
SYSTEM COULD PRODUCE PERIODS OF THUNDERSTORMS ACROSS THE LAKE AND
ALSO ADDITIONAL PERIODS OF SIGNIFICANT WINDS.

KJB

&&

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

&&

$$

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 210805
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
305 AM CDT MON APR 21 2014

.DISCUSSION...
305 AM CDT

MAIN FORECAST CONCERN IS WITH RAIN/THUNDER CHANCES AND TRENDS TODAY
WITH COLD FRONT MOVING THROUGH THE FORECAST AREA THIS AFTERNOON AND
EARLY THIS EVENING. PATTERN REMAINS AMPLIFIED AND PROGRESSIVE
THROUGH THE WEEK...WITH ANOTHER ORGANIZED CHANCE OF PRECIP AND A
FRONTAL PASSAGE THURSDAY AND YET ANOTHER LATER NEXT WEEKEND.

EARLY MORNING SURFACE MAP DEPICTS A TROUGH OF LOW PRESSURE EXTENDING
FROM NORTHWEST MINNESOTA SOUTHWEST THROUGH THE SIOUX FALLS AREA AND
INTO THE CENTRAL PLAINS. A COMPLEX UPPER TROUGH WAS OVER CENTRAL
NORTH AMERICA WITH AT LEAST THREE DISTINCT SHORT WAVE DISTURBANCES
FROM NORTH TO SOUTH PER 00Z RAOB AND CURRENT GOES VAPOR IMAGERY. THE
UPPER TROUGH IS PROGGED TO CONTINUE TO PROPAGATE EAST ACROSS THE
AREA TODAY...WITH SURFACE LOW PRESSURE LIFTING NORTH OF THE CWA AND
DEEPENING ACROSS THE NORTHERN GREAT LAKES IN RESPONSE TO THE
STRONGER NORTHERN STREAM SHORT WAVE DIGGING ALONG THE US/CANADIAN
BORDER. LOW LEVEL MOISTURE PLUME FROM TEXAS TO THE UPPER MISSISSIPPI
VALLEY HAS BEEN LIMITED SOMEWHAT BY PIECEMEAL NATURE OF UPPER
FORCING ALONG UPPER TROUGH AND BLOCKING OF CENTRAL/EASTERN GULF BY
EXPANSIVE SURFACE HIGH PRESSURE RIDGE WHICH EXTENDS FROM THE LOWER
MISSISSIPPI VALLEY TO OFF THE NEW ENGLAND COAST. HOWEVER...STARTING
TO SEE DEVELOPMENT OF ISOLATED SHRA/TSRA INTO FAR NORTHERN
IL/SOUTHERN WI EARLY THIS MORNING IN ADVANCE OF APPROACHING SHORT
WAVE AND ABOVE SUBTLE ELEVATED WARM FRONTAL ZONE WHICH STRETCHES
EAST/SOUTHEAST FROM SIOUX FALLS LOW. GUIDANCE RUNS IN GENERAL
AGREEMENT THAT PRECIP CHANCES WILL SLOWLY EXPAND ACROSS THE REGION
BY THIS AFTERNOON AS SURFACE COLD FRONT TRACKS EAST INTO THE AREA AS
SURFACE LOW DEEPENS TO OUR NORTH. COMBINATION OF LARGE SCALE ASCENT
ASSOCIATED WITH MID-LEVEL TROUGH AND LOW LEVEL FRONTAL CONVERGENCE
RESULTS IN STEEPENING LAPSE RATES BY AFTERNOON...WITH FORECAST
SOUNDINGS DEPICTING ABOUT 300-700 J/KG MLCAPE IN PRE-COLD FRONTAL
ENVIRONMENT. THIS IS EXPECTED TO BE SUFFICIENT TO PRODUCE INCREASING
COVERAGE OF SHRA/TSRA AS THE FRONT MOVES EAST ACROSS THE REGION THIS
AFTERNOON AND EARLY THIS EVENING...THOUGH DEEP SHEAR REMAINS
RELATIVELY WEAK WITH MAIN UPPER JET CORE WELL TO OUR NORTH. PRECIP
CHANCES THEN DIMINISH RAPIDLY FROM THE WEST/NORTHWEST THIS EVENING
AS FRONT PULLS AWAY TO THE EAST AND DRIER AIR PUSHES IN FROM THE
NORTHWEST. LOW LEVEL THERMAL RIDGE AHEAD OF COLD FRONT SHOULD EASILY
SUPPORT TEMPS IN THE 70S AGAIN TODAY...WITH SOUTHWEST BOUNDARY LAYER
FLOW 10-15 KT ENOUGH TO PREVENT ANY SIGNIFICANT LAKE BREEZE
DEVELOPMENT.

STRONG SHORT WAVE DIGS SOUTHEAST ACROSS THE GREAT LAKES REGION
TONIGHT...WITH COOL/DRY LOW LEVEL ADVECTION IN THE WAKE OF
ASSOCIATED SURFACE LOW AND COLD FRONT RESULTING IN COOLER TEMPS
TONIGHT AND TUESDAY...WITH NORTHERLY WINDS AHEAD OF SURFACE HIGH
PRESSURE WHICH BUILDS INTO THE AREA TUESDAY NIGHT AND WEDNESDAY.
WHILE IT WILL BE SUNNY...AFTER A COUPLE OF DAYS WELL INTO THE
70S...LOWER 60S APPEARS TO BE ABOUT THE WARMEST ACROSS OUR FAR
WESTERN/SOUTHERN COUNTIES ON TUESDAY AND WEDNESDAY WHILE NORTHEAST
WINDS OFF LAKE MICHIGAN LIMIT CHICAGO METRO AREA TO MID-UPPER
50S...WITH SOME 40S RIGHT ALONG THE LAKE. LOWS MAY DIP INTO THE LOW
30S IN SOME SPOTS TUESDAY NIGHT AS WINDS DIMINISH WITH THE APPROACH
OF THE RIDGE AXIS.

MEDIUM RANGE FORECASTS REMAIN CONSISTENT IN BRINGING ANOTHER RATHER
AMPLIFIED UPPER TROUGH EAST OF THE ROCKIES ON WEDNESDAY...WITH
SURFACE LOW PRESSURE DEVELOPING ACROSS THE PLAINS. MOISTURE RETURN
LOOKS TO BE A LITTLE MORE ROBUST WITH THIS FEATURE...WITH MOISTENING
AND SATURATION IN ISENTROPIC WARM AIR ADVECTION POTENTIALLY YIELDING
SOME SHOWERS ACROSS PARTS OF NORTHWEST IL BY WEDNESDAY AFTERNOON...
AND ACROSS MUCH OF THE FORECAST AREA WEDNESDAY NIGHT. THE GREATEST
CHANCE FOR PRECIP IS THURSDAY...AS OCCLUDING COLD FRONT PLOWS EAST
ACROSS THE CWA. WHILE TEMPS WARM...POSITION OF TRIPLE POINT IN
OCCLUSION REMAINS ACROSS/SOUTH OF OUR AREA AND DOES NOT PORTENT
TEMPS AS WARM AS THIS PAST WEEKEND WITH GENERALLY 60S ANTICIPATED
AND PERHAPS ONLY 50S ALONG NORTH SHORE IN SOUTHEAST FLOW. MODELS
DEPICT SECOND DISTURBANCE ROTATING AROUND UPPER LOW TO OUR NORTH
THURSDAY NIGHT INTO FRIDAY...WRAPPING A SECONDARY COLD FRONT
SOUTHEAST ACROSS THE AREA AND MAINTAINING SOME POTENTIAL FOR SHOWERS
ACROSS ESPECIALLY NORTHERN/EASTERN PARTS OF THE FORECAST AREA. SOME
DIFFERENCES ARISE WITH ORIENTATION OF EASTERN NORTH AMERICAN TROUGH
WHICH RESULTS BY NEXT WEEKEND... THOUGH LOOKS TO BE ANOTHER COOLER
THAN NORMAL PERIOD WITH NORTH/NORTHEAST FLOW FOR US TO THE WEST OF
THE UPPER TROUGH.
WHILE RUN TO RUN CONSISTENCY EXISTS IN GFS AND ECMWF LONG RANGE
SOLUTIONS...ECMWF REMAINS FASTER WITH DEPARTING EAST COAST LONG WAVE
TROUGH AND BRINGS ANOTHER LOW/WARM FRONT INTO THE REGION (BUT TO OUR
SOUTH) LATE SATURDAY AND SUNDAY. HAVE GENERALLY FOLLOWED THE ECMWF
TREND WHICH BRINGS PRECIP CHANCE BACK IN NORTH OF THE WARM FRONT
SATURDAY NIGHT/SUNDAY.

RATZER

&&

.AVIATION...

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

* SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING MONDAY AFTERNOON.

RODRIGUEZ

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

QUIET CONDITIONS TONIGHT/EARLY MONDAY MORNING...WITH MID/HIGH
LEVEL CLOUD COVER CONTINUING TO STREAM OVERHEAD AND SOUTH TO
SOUTHWEST WINDS REMAINING IN PLACE. EXPECT WINDS TO BECOME MORE
SOUTHWEST BY MID MORNING MONDAY WHILE SPEEDS INCREASE THROUGH MID
DAY AND THE AFTERNOON. EXPECT CLOUD COVER TO INCREASE WITH VFR
CEILINGS LIKELY BY MID DAY...AS SCATTERED SHOWERS BEGIN MOVING
ACROSS THE TERMINALS. THIS SCATTERED DEVELOPMENT WILL LIKELY
PERSIST IN THE AFTERNOON UNTIL BETTER DEVELOPMENT ARRIVES OUT
AHEAD OF APPROACHING FRONT LATE IN THE AFTERNOON AND EARLY
EVENING. ITS DURING THIS TIME THAT BEST THUNDER POTENTIAL WILL BE
BEFORE PRECIP QUICKLY EXITS TO THE EAST WITH FROPA...AND WITH
SOUTHWEST TO WEST WINDS TURNING TO THE NORTHWEST.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM HIGH CONFIDENCE WITH SHOWER/THUNDERSTORM POTENTIAL...WITH
  MEDIUM CONFIDENCE OF TIMING/DURATION.

RODRIGUEZ

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
125 PM CDT

LOW PRESSURE TRACKING ACROSS NORTHERN ONTARIO...WILL PUSH A
FRONTAL BOUNDARY ACROSS THE NORTHERN PORTION OF THE LAKE TONIGHT
INTO MONDAY. THIS WILL SET UP A PERIOD OF LIGHT AND VARIABLE
WINDS THERE THROUGH MONDAY. A SECOND AREA OF LOW PRESSURE WILL
MOVE ALONG THIS FRONT LATE MONDAY...AND ONCE THIS LOW MOVES EAST
OF THE LAKE...A PERIOD OF STRONGER NORTHERLY WINDS WILL SET UP
ACROSS THE LAKE MONDAY NIGHT INTO TUESDAY...BEFORE HIGH PRESSURE
BUILDS OVER THE LAKE WEDNESDAY NIGHT. THESE STRONGER NORTHERLY
WINDS COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS WITH HIGH
WAVES INTO THE NEAR SHORE WATERS FOR TUESDAY.

THE LATER PORTION OF THE WEEK APPEARS TO REMAIN ACTIVE
ACROSS THE GREAT LAKES REGION. IT APPEARS THAT ANOTHER SIGNIFICANT
AREA OF LOW PRESSURE WILL IMPACT THE UPPER MIDWEST AND THE GREAT
LAKES REGION LATE IN THE WEEK AND INTO EARLY NEXT WEEKEND. THIS
SYSTEM COULD PRODUCE PERIODS OF THUNDERSTORMS ACROSS THE LAKE AND
ALSO ADDITIONAL PERIODS OF SIGNIFICANT WINDS.

KJB

&&

.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 210544
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1244 AM CDT MON APR 21 2014

.DISCUSSION...
259 PM CDT

THIS AFTERNOON THROUGH TONIGHT...
SKIES HAVE REMAINED MOSTLY SUNNY THIS AFTERNOON...AND WITH
SOUTHERLY FLOW HAS ALLOWED SFC TEMPS TO QUICKLY PUSH WELL INTO THE
70S ACROSS THE BULK OF THE FORECAST AREA WITH A HANDFUL OF POINTS
AT 80 DEGREES. DEW POINTS WERE ABLE TO RISE TO ARND 40...HOWEVER
WITH FULL SUNSHINE THE MIXING HAS BEEN EFFECTIVE AT PRODUCING SOME
SUBSIDENCE AND PUSHED DEW POINTS BACK INTO THE UPR 30S. WHILE THE
ANTI-CYCLONIC FEATURE HAS BECOME CENTERED WELL EAST OF THE
REGION...ENOUGH OF AN INFLUENCE REMAINS ACROSS THE WESTERN OHIO
VALLEY AND THE FORECAST AREA THAT DRY WEATHER WILL PREVAIL THROUGH
THE EVENING AND LIKELY THRU THE OVERNIGHT.

THERE IS SOME CONCERN THAT THE ISOLATED SHOWERS/THUNDERSTORMS THAT
DEVELOPED THIS AFTERNOON ACROSS NORTHERN IOWA MAY CREEP
EAST...HOWEVER FEEL THAT WITH THE SOUTHERLY FLOW THIS AREA OF PRECIP
SHUD BE ABLE TO LIFT NORTHEAST AND REMAIN WEST/NORTHWEST OF THE CWFA
THIS EVENING/OVERNIGHT. TONIGHT WILL REMAIN MILD WITH TEMPS HOLDING
IN THE LOW/MID 50S. THE COOLEST LOCATIONS WILL LIKELY BE FOCUSED
NEAR LAKE MICHIGAN.

CONFIDENCE IN DRY WEATHER THRU OVERNIGHT...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

MONDAY THROUGH TUESDAY...
MID-LVL HEIGHTS BEGIN TO LOWER EARLY MON...HOWEVER LOW/MID LEVELS
REMAIN MOISTURE STARVED. THE MID-LVL WEAK VORT IS PROGGED TO SLIDE
EAST INTO THE OZARKS EARLY MON MORNING...AND WITH THE SOUTHERLY FLOW
OUT AHEAD OF THIS FEATURE...LLVLS SHOULD SLOWLY MOISTEN. GUIDANCE
HAS BEEN STEADILY BACKING OFF ON PRECIP CHANCES ARRIVING ACROSS THE
FORECAST AREA...AND HAVE TRIMMED BACK POPS ACCORDINGLY. INSTABILITY
DOES BUMP UP CLOSER TO MIDDAY MON...HOWEVER THE PEAK INSTABILITY
TIMEFRAME APPEARS TO BE FOCUSED BETWEEN 21-00Z.

NORTHERN STREAM MID-LVL VORT PIVOTS EAST ACROSS NORTHERN WISC MON
AFTN...WHICH MAY PROVIDE SOME ADDED FORCING AS THE FRONTAL BOUNDARY
NEARS THE CWFA. EXPECT PRECIP COVERAGE TO REMAIN LOW. GIVEN THE
INSTABILITY PROGGED TO BE NEARING 400-600J/KG BASED OFF OF LOCAL
WRF...THIS CONTINUES TO SUPPORT THINKING OF CHC THUNDER. SPC
CONTINUES TO HAVE THE AREA HIGHLIGHTED FOR GENERAL THUNDER. TEMPS
WILL ONCE AGAIN STEADILY WARM INTO THE MID/UPR 70S. COULD SEE A FEW
POINTS STILL TOUCH 80 DEGREES...ALTHOUGH WITH SLIGHTLY HIGHER LLVL
MOISTURE THE RATE OF CLIMB MAY BE DIMINISHED AND TEMPS COULD HOLD
GENERALLY IN THE MID 70S.

THE FRONTAL BOUNDARY SHUD NEAR THE NORTHWEST CWFA ARND 00Z...AND
WILL STEADILY BRING DRIER AIR IN AND SHUT-OFF PRECIP FROM NORTHWEST
TO SOUTHEAST. HAVE PUSHED UP THE ENDING TIME OF POPS CLOSER TO 6Z
TUE...AS WINDS TURN NORTHWEST.

MID-LVL TROUGH PIVOTS OVERHEAD MIDDAY TUE. THE SFC RIDGE CENTER WILL
BE CENTERED NORTHWEST OF THE CWFA TUE...THIS WILL KEEP TEMPS HELD
DOWN IN THE MID/UPR 50S AND LIKELY UPR 40S FOR LOCATIONS ADJACENT TO
LAKE MICHIGAN. THE FAR SOUTH/SOUTHWEST CWFA SHOULD BE ABLE TO WARM
BACK TO ARND 60.

CONFIDENCE IN PRECIP MON...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

WEDNESDAY THROUGH SUNDAY...
ANTI-CYCLONIC FLOW WILL SETUP SHOP ACROSS THE REGION WED. WITH LIGHT
EAST/NORTHEAST FLOW OFF OF LAKE MICHIGAN...TEMPS WILL STRUGGLE TO
WARM BEYOND THE UPR 40S/LOW 50S FOR AREAS ADJACENT TO THE LAKE.
INLAND AREAS WILL WARM INTO THE UPR 50S TO LOW 60S WED.

THEN THE FOCUS TURNS TOWARDS THE NEXT WEATHER SYSTEM POISED TO TAKE
SHAPE ACROSS THE CENTRAL PLAINS WED NGT. GUIDANCE HAS BEEN RATHER
CONSISTENT WITH THE SFC RIDGE SLIDING EAST OF THE FORECAST AREA LATE
WED NGT...WITH A WARM FRONTAL BOUNDARY LIFTING NORTH FROM THE SFC
LOW AND BRINGING PRECIP CHCS BACK TO THE AREA. GUIDANCE PROGS THE
TRACK OF THE SFC LOW TO BE LIFTING NORTHEAST INTO THE UPPER MIDWEST
THUR MORNING. INSTABILITY DOES APPEAR LIKELY TO DEVELOP AND INCREASE
FOR THUR...THUS HAVE HELD ONTO THE MENTION OF THUNDER. FRONTAL
BOUNDARY SHUD ARRIVE OVER THE AREA FRI...WHICH WILL BRING AN END TO
THE CONVECTIVE CHANCES. GUIDANCE INDICATES A DRY WEDGE LIFTING
NORTHEAST INTO THE FORECAST AREA FRI.

DEPENDING ON CLOUD COVER FRI...TEMPS MAY BE ABLE TO WARM BACK INTO
THE MID/UPR 60S OR POSSIBLY LOW 70S ACROSS THE SOUTHERN CWFA. THEN
FOR THE UPCOMING WEEKEND TEMPS ARE BACK INTO THE MID/UPR 50S.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

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

* SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING MONDAY AFTERNOON.

RODRIGUEZ

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

QUIET CONDITIONS TONIGHT/EARLY MONDAY MORNING...WITH MID/HIGH
LEVEL CLOUD COVER CONTINUING TO STREAM OVERHEAD AND SOUTH TO
SOUTHWEST WINDS REMAINING IN PLACE. EXPECT WINDS TO BECOME MORE
SOUTHWEST BY MID MORNING MONDAY WHILE SPEEDS INCREASE THROUGH MID
DAY AND THE AFTERNOON. EXPECT CLOUD COVER TO INCREASE WITH VFR
CEILINGS LIKELY BY MID DAY...AS SCATTERED SHOWERS BEGIN MOVING
ACROSS THE TERMINALS. THIS SCATTERED DEVELOPMENT WILL LIKELY
PERSIST IN THE AFTERNOON UNTIL BETTER DEVELOPMENT ARRIVES OUT
AHEAD OF APPROACHING FRONT LATE IN THE AFTERNOON AND EARLY
EVENING. ITS DURING THIS TIME THAT BEST THUNDER POTENTIAL WILL BE
BEFORE PRECIP QUICKLY EXITS TO THE EAST WITH FROPA...AND WITH
SOUTHWEST TO WEST WINDS TURNING TO THE NORTHWEST.

RODRIGUEZ


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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* MEDIUM HIGH CONFIDENCE WITH SHOWER/THUNDERSTORM POTENTIAL...WITH
  MEDIUM CONFIDENCE OF TIMING/DURATION.

RODRIGUEZ

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
125 PM CDT

LOW PRESSURE TRACKING ACROSS NORTHERN ONTARIO...WILL PUSH A
FRONTAL BOUNDARY ACROSS THE NORTHERN PORTION OF THE LAKE TONIGHT
INTO MONDAY. THIS WILL SET UP A PERIOD OF LIGHT AND VARIABLE
WINDS THERE THROUGH MONDAY. A SECOND AREA OF LOW PRESSURE WILL
MOVE ALONG THIS FRONT LATE MONDAY...AND ONCE THIS LOW MOVES EAST
OF THE LAKE...A PERIOD OF STRONGER NORTHERLY WINDS WILL SET UP
ACROSS THE LAKE MONDAY NIGHT INTO TUESDAY...BEFORE HIGH PRESSURE
BUILDS OVER THE LAKE WEDNESDAY NIGHT. THESE STRONGER NORTHERLY
WINDS COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS WITH HIGH
WAVES INTO THE NEAR SHORE WATERS FOR TUESDAY.

THE LATER PORTION OF THE WEEK APPEARS TO REMAIN ACTIVE
ACROSS THE GREAT LAKES REGION. IT APPEARS THAT ANOTHER SIGNIFICANT
AREA OF LOW PRESSURE WILL IMPACT THE UPPER MIDWEST AND THE GREAT
LAKES REGION LATE IN THE WEEK AND INTO EARLY NEXT WEEKEND. THIS
SYSTEM COULD PRODUCE PERIODS OF THUNDERSTORMS ACROSS THE LAKE AND
ALSO ADDITIONAL PERIODS OF SIGNIFICANT WINDS.

KJB

&&

.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 210255
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
955 PM CDT SUN APR 20 2014

.DISCUSSION...
259 PM CDT

THIS AFTERNOON THROUGH TONIGHT...
SKIES HAVE REMAINED MOSTLY SUNNY THIS AFTERNOON...AND WITH
SOUTHERLY FLOW HAS ALLOWED SFC TEMPS TO QUICKLY PUSH WELL INTO THE
70S ACROSS THE BULK OF THE FORECAST AREA WITH A HANDFUL OF POINTS
AT 80 DEGREES. DEW POINTS WERE ABLE TO RISE TO ARND 40...HOWEVER
WITH FULL SUNSHINE THE MIXING HAS BEEN EFFECTIVE AT PRODUCING SOME
SUBSIDENCE AND PUSHED DEW POINTS BACK INTO THE UPR 30S. WHILE THE
ANTI-CYCLONIC FEATURE HAS BECOME CENTERED WELL EAST OF THE
REGION...ENOUGH OF AN INFLUENCE REMAINS ACROSS THE WESTERN OHIO
VALLEY AND THE FORECAST AREA THAT DRY WEATHER WILL PREVAIL THROUGH
THE EVENING AND LIKELY THRU THE OVERNIGHT.

THERE IS SOME CONCERN THAT THE ISOLATED SHOWERS/THUNDERSTORMS THAT
DEVELOPED THIS AFTERNOON ACROSS NORTHERN IOWA MAY CREEP
EAST...HOWEVER FEEL THAT WITH THE SOUTHERLY FLOW THIS AREA OF PRECIP
SHUD BE ABLE TO LIFT NORTHEAST AND REMAIN WEST/NORTHWEST OF THE CWFA
THIS EVENING/OVERNIGHT. TONIGHT WILL REMAIN MILD WITH TEMPS HOLDING
IN THE LOW/MID 50S. THE COOLEST LOCATIONS WILL LIKELY BE FOCUSED
NEAR LAKE MICHIGAN.

CONFIDENCE IN DRY WEATHER THRU OVERNIGHT...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

MONDAY THROUGH TUESDAY...
MID-LVL HEIGHTS BEGIN TO LOWER EARLY MON...HOWEVER LOW/MID LEVELS
REMAIN MOISTURE STARVED. THE MID-LVL WEAK VORT IS PROGGED TO SLIDE
EAST INTO THE OZARKS EARLY MON MORNING...AND WITH THE SOUTHERLY FLOW
OUT AHEAD OF THIS FEATURE...LLVLS SHOULD SLOWLY MOISTEN. GUIDANCE
HAS BEEN STEADILY BACKING OFF ON PRECIP CHANCES ARRIVING ACROSS THE
FORECAST AREA...AND HAVE TRIMMED BACK POPS ACCORDINGLY. INSTABILITY
DOES BUMP UP CLOSER TO MIDDAY MON...HOWEVER THE PEAK INSTABILITY
TIMEFRAME APPEARS TO BE FOCUSED BETWEEN 21-00Z.

NORTHERN STREAM MID-LVL VORT PIVOTS EAST ACROSS NORTHERN WISC MON
AFTN...WHICH MAY PROVIDE SOME ADDED FORCING AS THE FRONTAL BOUNDARY
NEARS THE CWFA. EXPECT PRECIP COVERAGE TO REMAIN LOW. GIVEN THE
INSTABILITY PROGGED TO BE NEARING 400-600J/KG BASED OFF OF LOCAL
WRF...THIS CONTINUES TO SUPPORT THINKING OF CHC THUNDER. SPC
CONTINUES TO HAVE THE AREA HIGHLIGHTED FOR GENERAL THUNDER. TEMPS
WILL ONCE AGAIN STEADILY WARM INTO THE MID/UPR 70S. COULD SEE A FEW
POINTS STILL TOUCH 80 DEGREES...ALTHOUGH WITH SLIGHTLY HIGHER LLVL
MOISTURE THE RATE OF CLIMB MAY BE DIMINISHED AND TEMPS COULD HOLD
GENERALLY IN THE MID 70S.

THE FRONTAL BOUNDARY SHUD NEAR THE NORTHWEST CWFA ARND 00Z...AND
WILL STEADILY BRING DRIER AIR IN AND SHUT-OFF PRECIP FROM NORTHWEST
TO SOUTHEAST. HAVE PUSHED UP THE ENDING TIME OF POPS CLOSER TO 6Z
TUE...AS WINDS TURN NORTHWEST.

MID-LVL TROUGH PIVOTS OVERHEAD MIDDAY TUE. THE SFC RIDGE CENTER WILL
BE CENTERED NORTHWEST OF THE CWFA TUE...THIS WILL KEEP TEMPS HELD
DOWN IN THE MID/UPR 50S AND LIKELY UPR 40S FOR LOCATIONS ADJACENT TO
LAKE MICHIGAN. THE FAR SOUTH/SOUTHWEST CWFA SHOULD BE ABLE TO WARM
BACK TO ARND 60.

CONFIDENCE IN PRECIP MON...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

WEDNESDAY THROUGH SUNDAY...
ANTI-CYCLONIC FLOW WILL SETUP SHOP ACROSS THE REGION WED. WITH LIGHT
EAST/NORTHEAST FLOW OFF OF LAKE MICHIGAN...TEMPS WILL STRUGGLE TO
WARM BEYOND THE UPR 40S/LOW 50S FOR AREAS ADJACENT TO THE LAKE.
INLAND AREAS WILL WARM INTO THE UPR 50S TO LOW 60S WED.

THEN THE FOCUS TURNS TOWARDS THE NEXT WEATHER SYSTEM POISED TO TAKE
SHAPE ACROSS THE CENTRAL PLAINS WED NGT. GUIDANCE HAS BEEN RATHER
CONSISTENT WITH THE SFC RIDGE SLIDING EAST OF THE FORECAST AREA LATE
WED NGT...WITH A WARM FRONTAL BOUNDARY LIFTING NORTH FROM THE SFC
LOW AND BRINGING PRECIP CHCS BACK TO THE AREA. GUIDANCE PROGS THE
TRACK OF THE SFC LOW TO BE LIFTING NORTHEAST INTO THE UPPER MIDWEST
THUR MORNING. INSTABILITY DOES APPEAR LIKELY TO DEVELOP AND INCREASE
FOR THUR...THUS HAVE HELD ONTO THE MENTION OF THUNDER. FRONTAL
BOUNDARY SHUD ARRIVE OVER THE AREA FRI...WHICH WILL BRING AN END TO
THE CONVECTIVE CHANCES. GUIDANCE INDICATES A DRY WEDGE LIFTING
NORTHEAST INTO THE FORECAST AREA FRI.

DEPENDING ON CLOUD COVER FRI...TEMPS MAY BE ABLE TO WARM BACK INTO
THE MID/UPR 60S OR POSSIBLY LOW 70S ACROSS THE SOUTHERN CWFA. THEN
FOR THE UPCOMING WEEKEND TEMPS ARE BACK INTO THE MID/UPR 50S.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

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

* SCT`D SHRA/TSRA LIKELY DEVELOPING MONDAY AFTERNOON

IZZI

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

NO SIGNIFICANT WEATHER EXPECTED UNTIL MONDAY AFTERNOON WHEN SCT`D
SHRA AND TSRA EXPECTED TO DEVELOP OVER NORTHERN ILLINOIS. AT THIS
POINT IT IS NOT LOOKING LIKE A HIGH COVERAGE/LONG DURATION EVENT
BUT PROBABILITY OF A BRIEF PERIOD OR TWO OF SHRA/TSRA LOOKS FAIRLY
HIGH. WINDS SHIFT TO NORTHWEST MONDAY EVENING...PRECIP SHOULD MOVE
OUT AROUND SUNSET AND THEN VFR CONDITIONS EXPECTED AGAIN.

IZZI

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

* MEDIUM CONFIDENCE IN COVERAGE/TIMING OF SHRA/TSRA MONDAY
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
125 PM CDT

LOW PRESSURE TRACKING ACROSS NORTHERN ONTARIO...WILL PUSH A
FRONTAL BOUNDARY ACROSS THE NORTHERN PORTION OF THE LAKE TONIGHT
INTO MONDAY. THIS WILL SET UP A PERIOD OF LIGHT AND VARIABLE
WINDS THERE THROUGH MONDAY. A SECOND AREA OF LOW PRESSURE WILL
MOVE ALONG THIS FRONT LATE MONDAY...AND ONCE THIS LOW MOVES EAST
OF THE LAKE...A PERIOD OF STRONGER NORTHERLY WINDS WILL SET UP
ACROSS THE LAKE MONDAY NIGHT INTO TUESDAY...BEFORE HIGH PRESSURE
BUILDS OVER THE LAKE WEDNESDAY NIGHT. THESE STRONGER NORTHERLY
WINDS COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS WITH HIGH
WAVES INTO THE NEAR SHORE WATERS FOR TUESDAY.

THE LATER PORTION OF THE WEEK APPEARS TO REMAIN ACTIVE
ACROSS THE GREAT LAKES REGION. IT APPEARS THAT ANOTHER SIGNIFICANT
AREA OF LOW PRESSURE WILL IMPACT THE UPPER MIDWEST AND THE GREAT
LAKES REGION LATE IN THE WEEK AND INTO EARLY NEXT WEEKEND. THIS
SYSTEM COULD PRODUCE PERIODS OF THUNDERSTORMS ACROSS THE LAKE AND
ALSO ADDITIONAL PERIODS OF SIGNIFICANT WINDS.

KJB

&&

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

$$

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000
FXUS63 KLOT 202338
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 PM CDT SUN APR 20 2014

.DISCUSSION...
259 PM CDT

THIS AFTERNOON THROUGH TONIGHT...
SKIES HAVE REMAINED MOSTLY SUNNY THIS AFTERNOON...AND WITH
SOUTHERLY FLOW HAS ALLOWED SFC TEMPS TO QUICKLY PUSH WELL INTO THE
70S ACROSS THE BULK OF THE FORECAST AREA WITH A HANDFUL OF POINTS
AT 80 DEGREES. DEW POINTS WERE ABLE TO RISE TO ARND 40...HOWEVER
WITH FULL SUNSHINE THE MIXING HAS BEEN EFFECTIVE AT PRODUCING SOME
SUBSIDENCE AND PUSHED DEW POINTS BACK INTO THE UPR 30S. WHILE THE
ANTI-CYCLONIC FEATURE HAS BECOME CENTERED WELL EAST OF THE
REGION...ENOUGH OF AN INFLUENCE REMAINS ACROSS THE WESTERN OHIO
VALLEY AND THE FORECAST AREA THAT DRY WEATHER WILL PREVAIL THROUGH
THE EVENING AND LIKELY THRU THE OVERNIGHT.

THERE IS SOME CONCERN THAT THE ISOLATED SHOWERS/THUNDERSTORMS THAT
DEVELOPED THIS AFTERNOON ACROSS NORTHERN IOWA MAY CREEP
EAST...HOWEVER FEEL THAT WITH THE SOUTHERLY FLOW THIS AREA OF PRECIP
SHUD BE ABLE TO LIFT NORTHEAST AND REMAIN WEST/NORTHWEST OF THE CWFA
THIS EVENING/OVERNIGHT. TONIGHT WILL REMAIN MILD WITH TEMPS HOLDING
IN THE LOW/MID 50S. THE COOLEST LOCATIONS WILL LIKELY BE FOCUSED
NEAR LAKE MICHIGAN.

CONFIDENCE IN DRY WEATHER THRU OVERNIGHT...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

MONDAY THROUGH TUESDAY...
MID-LVL HEIGHTS BEGIN TO LOWER EARLY MON...HOWEVER LOW/MID LEVELS
REMAIN MOISTURE STARVED. THE MID-LVL WEAK VORT IS PROGGED TO SLIDE
EAST INTO THE OZARKS EARLY MON MORNING...AND WITH THE SOUTHERLY FLOW
OUT AHEAD OF THIS FEATURE...LLVLS SHOULD SLOWLY MOISTEN. GUIDANCE
HAS BEEN STEADILY BACKING OFF ON PRECIP CHANCES ARRIVING ACROSS THE
FORECAST AREA...AND HAVE TRIMMED BACK POPS ACCORDINGLY. INSTABILITY
DOES BUMP UP CLOSER TO MIDDAY MON...HOWEVER THE PEAK INSTABILITY
TIMEFRAME APPEARS TO BE FOCUSED BETWEEN 21-00Z.

NORTHERN STREAM MID-LVL VORT PIVOTS EAST ACROSS NORTHERN WISC MON
AFTN...WHICH MAY PROVIDE SOME ADDED FORCING AS THE FRONTAL BOUNDARY
NEARS THE CWFA. EXPECT PRECIP COVERAGE TO REMAIN LOW. GIVEN THE
INSTABILITY PROGGED TO BE NEARING 400-600J/KG BASED OFF OF LOCAL
WRF...THIS CONTINUES TO SUPPORT THINKING OF CHC THUNDER. SPC
CONTINUES TO HAVE THE AREA HIGHLIGHTED FOR GENERAL THUNDER. TEMPS
WILL ONCE AGAIN STEADILY WARM INTO THE MID/UPR 70S. COULD SEE A FEW
POINTS STILL TOUCH 80 DEGREES...ALTHOUGH WITH SLIGHTLY HIGHER LLVL
MOISTURE THE RATE OF CLIMB MAY BE DIMINISHED AND TEMPS COULD HOLD
GENERALLY IN THE MID 70S.

THE FRONTAL BOUNDARY SHUD NEAR THE NORTHWEST CWFA ARND 00Z...AND
WILL STEADILY BRING DRIER AIR IN AND SHUT-OFF PRECIP FROM NORTHWEST
TO SOUTHEAST. HAVE PUSHED UP THE ENDING TIME OF POPS CLOSER TO 6Z
TUE...AS WINDS TURN NORTHWEST.

MID-LVL TROUGH PIVOTS OVERHEAD MIDDAY TUE. THE SFC RIDGE CENTER WILL
BE CENTERED NORTHWEST OF THE CWFA TUE...THIS WILL KEEP TEMPS HELD
DOWN IN THE MID/UPR 50S AND LIKELY UPR 40S FOR LOCATIONS ADJACENT TO
LAKE MICHIGAN. THE FAR SOUTH/SOUTHWEST CWFA SHOULD BE ABLE TO WARM
BACK TO ARND 60.

CONFIDENCE IN PRECIP MON...MEDIUM/HIGH.
CONFIDENCE IN TEMPS...HIGH.

WEDNESDAY THROUGH SUNDAY...
ANTI-CYCLONIC FLOW WILL SETUP SHOP ACROSS THE REGION WED. WITH LIGHT
EAST/NORTHEAST FLOW OFF OF LAKE MICHIGAN...TEMPS WILL STRUGGLE TO
WARM BEYOND THE UPR 40S/LOW 50S FOR AREAS ADJACENT TO THE LAKE.
INLAND AREAS WILL WARM INTO THE UPR 50S TO LOW 60S WED.

THEN THE FOCUS TURNS TOWARDS THE NEXT WEATHER SYSTEM POISED TO TAKE
SHAPE ACROSS THE CENTRAL PLAINS WED NGT. GUIDANCE HAS BEEN RATHER
CONSISTENT WITH THE SFC RIDGE SLIDING EAST OF THE FORECAST AREA LATE
WED NGT...WITH A WARM FRONTAL BOUNDARY LIFTING NORTH FROM THE SFC
LOW AND BRINGING PRECIP CHCS BACK TO THE AREA. GUIDANCE PROGS THE
TRACK OF THE SFC LOW TO BE LIFTING NORTHEAST INTO THE UPPER MIDWEST
THUR MORNING. INSTABILITY DOES APPEAR LIKELY TO DEVELOP AND INCREASE
FOR THUR...THUS HAVE HELD ONTO THE MENTION OF THUNDER. FRONTAL
BOUNDARY SHUD ARRIVE OVER THE AREA FRI...WHICH WILL BRING AN END TO
THE CONVECTIVE CHANCES. GUIDANCE INDICATES A DRY WEDGE LIFTING
NORTHEAST INTO THE FORECAST AREA FRI.

DEPENDING ON CLOUD COVER FRI...TEMPS MAY BE ABLE TO WARM BACK INTO
THE MID/UPR 60S OR POSSIBLY LOW 70S ACROSS THE SOUTHERN CWFA. THEN
FOR THE UPCOMING WEEKEND TEMPS ARE BACK INTO THE MID/UPR 50S.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

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

* SCT`D SHRA/TSRA LIKELY MONDAY AFTERNOON

IZZI

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

NO SIGNIFICANT WEATHER EXPECTED UNTIL MONDAY AFTERNOON WHEN SCT`D
SHRA AND TSRA EXPECTED TO DEVELOP OVER NORTHERN ILLINOIS. AT THIS
POINT IT IS NOT LOOKING LIKE A HIGH COVERAGE/LONG DURATION EVENT
BUT PROBABILITY OF A BRIEF PERIOD OR TWO OF SHRA/TSRA LOOKS FAIRLY
HIGH. WINDS SHIFT TO NORTHWEST MONDAY EVENING...PRECIP SHOULD MOVE
OUT AROUND SUNSET AND THEN VFR CONDITIONS EXPECTED AGAIN.

IZZI


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

* MEDIUM CONFIDENCE IN COVERAGE/TIMING OF SHRA/TSRA MONDAY
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

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

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...VFR EARLY...THEN A PERIOD OF SHRA/TSRA LIKELY LATE.

FRIDAY AND SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

.MARINE...
125 PM CDT

LOW PRESSURE TRACKING ACROSS NORTHERN ONTARIO...WILL PUSH A
FRONTAL BOUNDARY ACROSS THE NORTHERN PORTION OF THE LAKE TONIGHT
INTO MONDAY. THIS WILL SET UP A PERIOD OF LIGHT AND VARIABLE
WINDS THERE THROUGH MONDAY. A SECOND AREA OF LOW PRESSURE WILL
MOVE ALONG THIS FRONT LATE MONDAY...AND ONCE THIS LOW MOVES EAST
OF THE LAKE...A PERIOD OF STRONGER NORTHERLY WINDS WILL SET UP
ACROSS THE LAKE MONDAY NIGHT INTO TUESDAY...BEFORE HIGH PRESSURE
BUILDS OVER THE LAKE WEDNESDAY NIGHT. THESE STRONGER NORTHERLY
WINDS COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS WITH HIGH
WAVES INTO THE NEAR SHORE WATERS FOR TUESDAY.

THE LATER PORTION OF THE WEEK APPEARS TO REMAIN ACTIVE
ACROSS THE GREAT LAKES REGION. IT APPEARS THAT ANOTHER SIGNIFICANT
AREA OF LOW PRESSURE WILL IMPACT THE UPPER MIDWEST AND THE GREAT
LAKES REGION LATE IN THE WEEK AND INTO EARLY NEXT WEEKEND. THIS
SYSTEM COULD PRODUCE PERIODS OF THUNDERSTORMS ACROSS THE LAKE AND
ALSO ADDITIONAL PERIODS OF SIGNIFICANT WINDS.

KJB

&&

.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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