Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240944
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
444 AM CDT THU APR 24 2014

.DISCUSSION...
351 AM CDT

MAIN FOCUS THIS MORNING IS WITH SLOWER PROGRESSION OF SURFACE LOW
AND COLD FRONT AND ASSOCIATED RAIN ESPECIALLY LATE TODAY/TONIGHT.
BREEZY/MILD DAY FRIDAY...BEFORE SECOND COLD FRONT PASSES FRIDAY
EVENING AND SETS STAGE FOR PROLONGED PERIOD OF COOL/WET WEATHER
ESPECIALLY SATURDAY NIGHT-WEDNESDAY.

BAND OF SHOWERS/GRAUPEL WITH LEAD SHORT WAVE TROUGH CONTINUES TO
LIFT NORTHEAST ACROSS NORTH/NORTHEAST PARTS OF THE CWA AT 0830Z.
DRYING EVIDENT UPSTREAM INTO WESTERN IL/MO...WITH NEAR TERM GUIDANCE
IN GOOD AGREEMENT IN SUGGESTING MOST OF FORECAST AREA WILL SEE DRY
WEATHER FOR MUCH OF THE MORNING/EARLY AFTERNOON HOURS AS INITIAL
ELEVATED WARM FRONTAL PRECIP LIFTS NORTH OF THE AREA. TREND IN MODEL
GUIDANCE OVER THE PAST 24 HOURS HAS BEEN TO SLOW EASTWARD
PROGRESSION OF COLD FRONT...WITH DEEPER SOUTHERN STREAM SHORT WAVE
ALSO RESULTING IN SURFACE LOW REFLECTION TRACKING FARTHER SOUTH
ACROSS CENTRAL IL. OVERALL...ONLY REAL CHANGE TO GOING FORECAST WAS
TO SLOW ARRIVAL AND DEPARTURE OF HIGHER POPS WITH THE FRONT THROUGH
TONIGHT.  WITH STEADIER RAINFALL TONIGHT...STILL LOOKS TO BE ABOUT A
HALF INCH AREA WIDE. FORECAST SOUNDINGS INDICATE LAPSE RATES NOT
PARTICULARLY IMPRESSIVE...AND HAVE ONLY INDICATED ISOLATED THUNDER
MAINLY WITH APPROACH OF COLD LATE TODAY/TONIGHT. FRONT CLEARS
EASTERN CWA AROUND SUNRISE FRIDAY MORNING...WITH WEAK FLAT SURFACE
RIDGE DEVELOPING ACROSS THE AREA DURING THE DAY. DEEPER MIXING AND
SUBSIDENCE INDICATE FRIDAY MAY BE THE MILDEST DAY OF THE STRETCH
WITH MID 60S-LOW 70S EXPECTED FROM FAR NORTH TO FAR SOUTH.

AS INDICATED OVER THE PAST FEW DAYS...ANOTHER COLD FRONT ASSOCIATED
WITH NORTHERN STREAM DISTURBANCE DOES SETTLE SOUTH ACROSS THE
FORECAST AREA FRIDAY EVENING. MODELS CONTINUE TO HAVE SOME
DIFFICULTY PINNING DOWN EXACT TIMING/PLACEMENT OF THE FRONT AS IT
SLOWS UP OVER CENTRAL IL/IN FRIDAY NIGHT...THOUGH MOST GUIDANCE DOES
INDICATE POTENTIAL FOR SOME SPOTTY LIGHT PRECIP AS FRONT UNDERCUTS
WEST-SOUTHWEST FLOW ALOFT. WITH CONFIDENCE IN TIMING/PLACEMENT OF
ANY LIGHT SHOWERS RATHER LOW...HAVE BROAD-BRUSHED SLIGHT CHANCE
OVERNIGHT THOUGH NOT EXPECTING RAIN TO AMOUNT TO MUCH.

BRIEF INTRUSION OF HIGH PRESSURE RIDGING FROM THE NORTH ON SATURDAY
EXPECTED TO YIELD DRY BUT COOLER WEATHER...BEFORE STATIONARY FRONTAL
BOUNDARY TO OUR SOUTH BECOMES FOCUS FOR PRECIP DEVELOPMENT SATURDAY
NIGHT THROUGH THE EXTENDED PORTION OF THE FORECAST AS CLOSED UPPER
LOW AND ITS ASSOCIATED SURFACE CIRCULATION SLOWLY WOBBLES FROM THE
PLAINS TO THE GREAT LAKES REGION THROUGH THE MIDDLE OF NEXT WEEK.
COOL AND GENERALLY WET WEATHER TO PREDOMINATE...WITH EAST-NORTHEAST
LOW LEVEL WINDS AND PERSISTENT MOIST ASCENT FROM THE SOUTH ABOVE THE
STATIONARY BAROCLINIC ZONE TO OUR SOUTH. GUIDANCE HAS TRENDED
GENERALLY WARMER ALOFT SUNDAY-TUESDAY...THOUGH AFOREMENTIONED LOW
LEVEL WINDS OFF LAKE MICHIGAN WILL LIKELY MAKE FOR A FAIRLY LARGE
GRADIENT FROM NORTH TO SOUTH FOR MUCH OF THE PERIOD...WITH HIGHS
ALONG THE LAKE IN THE 40S...WHILE 60S ARE MORE PREVALENT SOUTH OF
THE I-80 CORRIDOR.

RATZER

&&

.AVIATION...

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

* STRONG/GUSTY SOUTHEAST WINDS TODAY.

* SHRA LATER THIS EVENING W/ ISOL TSRA.

* POSSIBLE LOW END MVFR CEILINGS LATE IN THE FORECAST PERIOD.

RODRIGUEZ

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

TERMINALS REMAIN ON EASTERN FRINGE OF PERSISTENT SHOWER
DEVELOPMENT AT THIS HOUR...AND NOW EXPECT THIS TO CONTINUE OVER
THE NEXT COUPLE OF HOURS BEFORE THIS PRECIP SHIELD ALL LIFTS TO
THE NORTH OF THE TERMINALS LATER THIS MORNING. ALTHOUGH...STILL
CONFIDENT THIS WILL REMAIN LIGHT WITH VFR CONDITIONS CONTINUING.
A LULL IN THE ACTIVITY AS WELL AS CLOUD COVER WILL LIKELY OCCUR
FOR THE REMAINDER OF THE DAY BEFORE THE NEXT SYSTEM CURRENTLY WELL
WEST OF THE TERMINALS SLOWLY APPROACHES. VFR CEILINGS WILL RETURN
LATE THIS AFTERNOON INTO THE EVENING AS WELL AS
SHOWER/THUNDERSTORM CHANCES. MAINTAINED JUST SHOWERS IN THE TAFS
WITH LOW CONFIDENCE OF TSRA AT THIS TIME...WITH EVEN SOME
POSSIBILITY OF DELAYING THE ONSET OF VCSH/-SHAR WITH LATER
FORECASTS. SOUTHEAST WINDS WILL RAMP UP RATHER QUICKLY LATER THIS
MORNING WITH STRONG GUSTS TO AROUND 30 KT LIKELY BEFORE A SLOW
DOWNWARD TREND OCCURS LATER THIS AFTERNOON. WITH CONFIDENCE LOWER
WITH REGARDS TO OVERALL TIMING OF THIS SYSTEM...HAVE LEFT OUT ANY
MENTION OF WIND SHIFT TO THE NORTHWEST AND POSSIBLE LOW END MVFR
CEILINGS VERY LATE IN THE FORECAST PERIOD FOR ORD.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* HIGH CONFIDENCE WITH SHOWERS LATER THIS EVENING...WITH LOW
  MEDIUM CONFIDENCE ON EXACT TIMING AND TSRA.

* LOW CONFIDENCE WITH LOW END MVFR CEILING CHANCES.

RODRIGUEZ

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

* FRIDAY AND SATURDAY...DRY/VFR.
* SUNDAY THROUGH TUESDAY...CHANCE OF SHRA. MVFR POSSIBLE.

&&

.MARINE...
443 AM CDT

LIGHTER FLOW REMAINING OVER THE LAKE EARLY THIS MORNING WITH
WEAKER SURFACE PATTERN STILL IN PLACE. ALTHOUGH...EXPECT EAST TO
SOUTHEAST WINDS TO RAPIDLY INCREASE THROUGH MID MORNING AND THEN
ESPECIALLY INTO THE AFTERNOON WHEN TO 30 KT WINDS WILL BE
OBSERVED...IN RESPONSE TO AN APPROACHING TROUGH OF LOW PRESSURE.
EAST TO SOUTHEAST WINDS WILL STILL REMAIN TO 30 KT THIS EVENING
BUT SLOWLY DIMINISH AS THIS TROUGH OF LOW PRESSURE MOVES THROUGH
THE REGION. WINDS WILL BEGIN TURNING TO THE WEST/NORTHEAST ON THE
BACKSIDE OF THIS SYSTEM LATE TONIGHT INTO FRIDAY BEFORE TURNING
MORE NORTHERLY FRIDAY NIGHT INTO SATURDAY.

RODRIGUEZ

&&

.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.

&&

$$

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