Area Forecast Discussion
Issued by NWS Chicago, IL

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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.
&&

$$

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