Area Forecast Discussion
Issued by NWS Chicago, IL

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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.

&&

$$

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