Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 201826
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
126 PM CDT SUN APR 20 2014

.DISCUSSION...
319 AM CDT

MAIN FORECAST CHALLENGES/CONCERNS ARE WITH MAX TEMPS TODAY WITH A
POSSIBILITY OF LAKE COOLING...AND THEN WITH INCREASING CHANCES FOR
SHOWERS AND THUNDERSTORMS ON MONDAY.

QUIET CONDITIONS CONTINUE THIS MORNING AS HIGH PRESSURE REMAINS
SITUATED ACROSS THE REGION...WHILE SURFACE TROUGH/BOUNDARY ARE
SITUATED WELL NORTHWEST OF THE CWA. MID/UPPER LEVEL PATTERN IS
FAIRLY ACTIVE ACROSS THE CONUS THIS MORNING WITH EXITING VORT MAX
TO THE NORTH AND APPROACHING WEAKER/LOW AMPLITUDE UPPER LEVEL
TROUGH LIFTING NORTHEAST TO THE SOUTHERN PLAINS...AND WITH ANOTHER
VORTICITY MAXIMA SHIFTING EAST THROUGH THE NORTHWEST CONUS. THESE
FEATURES HAVE PROVIDED A FAIR AMOUNT OF MID AND HIGH LEVEL
MOISTURE OVER THE CENTRAL CONUS...BUT WITH THE MAJORITY OF THIS
MOISTURE STAYING WEST OF THE CWA. WITH THE FRONTAL BOUNDARY HELD
UP TO THE NORTHWEST TODAY...EXPECT DRY CONDITIONS ONCE AGAIN TODAY
AND FOR MOST OF TONIGHT BUT WITH A SLOW INCREASE IN CLOUD COVER
THROUGHOUT THE DAY. LATEST SATELLITE IMAGERY DEPICTING MID/HIGH
LEVEL CLOUD COVER TRYING TO INCH ITS WAY CLOSER TO THE WEST AND
NORTHWEST CWA AND ALTHOUGH I DO ANTICIPATE A PORTION OF THIS CLOUD
COVER TO CLIP THE FAR NORTHWEST AND NORTHERN CWA...BULK OF THIS
CLOUD COVER SHOULD REMAIN OUTSIDE OF THE CWA THROUGH EARLY
AFTERNOON. COULD SEE SOME OF THIS CLOUD COVER SPILL FURTHER EAST
FOR SOME PERIODS TODAY...BUT STILL THINK IT WONT BE ENOUGH TO
PROVIDE ANYTHING MORE THAN PARTLY CLOUDY SKIES. EVEN WITH
POTENTIAL FOR CLOUDS TO PUSH ACROSS A PORTION OF THE CWA...FEEL
THAT TODAY WILL BE A RATHER WARM DAY WITH WELL ABOVE NORMAL TEMPS
IN THE MID TO UPPER 70S ACROSS THE CWA. AS WAA STEERS THERMAL AXIS
OVERHEAD TODAY...DID RAISE TEMPS A COUPLE OF DEGREES WITH MOST
LOCATIONS OBSERVING THESE MID/UPPER 70 DEGREE TEMPS WITH LOCATIONS
ACROSS THE EASTERN CWA LIKELY MORE IN THE LOW 70 RANGE. LAKE
COOLING COULD BECOME AN ISSUE LATER THIS AFTERNOON AS SURFACE
PATTERN RELAXES AND LOW LEVEL FLOW WEAKENS. THIS COULD RELAX THE
SURFACE WINDS ENOUGH TO ALLOW FOR SOME ONSHORE TURNING OF THE
WINDS MAINLY FOR CHICAGO NORTHWARD INTO LAKE COUNTY...WITH A
SLIGHT POSSIBILITY FOR THIS TO OCCUR OVER NORTHWEST INDIANA.
ALTHOUGH DID ACCOUNT FOR THIS IN THE MAX T GRID...FEEL THAT MOST
OF THE WARMING WILL OCCUR PRIOR TO THIS TURNING OF THE WINDS AND
RESULTANT COOLING. SO LOCATIONS NEAR THE LAKE WILL LIKELY OBSERVE
UPPER 60S OR LOWER 70S BEFORE THIS POSSIBLE COOLING OCCURS LATER
THIS AFTERNOON.

EXPECT TONIGHT TO REMAIN ON THE DRY SIDE BUT WITH SOME POSSIBILITY
FOR A STRAY SHOWER OR TWO MORE TO MOVE ACROSS THE FAR NORTHWEST
CWA MORE TOWARDS EARLY MONDAY MORNING. AS SEVERAL WAVES OF ENERGY
LIFT NORTHEAST OUT AHEAD OF APPROACHING TROUGH TO THE SOUTHWEST
AND THE STRONGER AND MORE DEFINED MID LEVEL TROUGH DROPS SOUTHEAST
THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST MONDAY...EXPECT
SURFACE TROUGH TO BECOME MORE ORGANIZED AND THEN DEEPEN AS IT
BEGINS WORKING EAST TOWARDS THE CWA BY MID DAY MONDAY.
ALTHOUGH...IT DOES APPEAR AS IF A SLOWER TREND IS SHOWING UP
WITHIN MODEL GUIDANCE AND HAVE REFLECTED THIS TREND IN THE GRIDS
KEEPING ONLY CHANCE POPS MAINLY FOR THE NORTHWEST HALF OF THE CWA
THROUGH MID DAY MONDAY. LARGE SCALE SUPPORT INCREASES AS WELL AS
LOW/MID LEVEL CONVERGENCE STRENGTHENING THROUGH THE AFTERNOON. AS
THIS OCCURS...IT DOES APPEAR THAT SOME BETTER MOISTURE RETURN DOES
FINALLY OCCUR OUT AHEAD OF THIS TROUGH/FRONTAL BOUNDARY. EXPECT
SCATTERED SHOWER DEVELOPMENT TO PERSIST THROUGH THE AFTERNOON WITH
THE BEST CHANCES FOR PRECIP ACROSS THE ENTIRE CWA EXPECTED DURING
THIS TIME FRAME. GUIDANCE HAS CONTINUED THE INCREASING INSTABILITY
TREND...WITH INSTABILITY AXIS NOW ANTICIPATED WELL INTO WISCONSIN
AND OUT OVER THE LAKE. DID INCREASE MENTION OF THUNDER...WITH
CHANCE THUNDER FOR THE ENTIRE CWA ON MONDAY. WITH FLOW ALOFT
RATHER WEAK AS WELL AS THE INSTABILITY TO BE ON THE WEAKER
SIDE...AT THIS TIME EXPECT ANY THUNDERSTORM DEVELOPMENT TO BE
WEAK/UNORGANIZED. TROUGH/FRONT WILL PUSH THROUGH MONDAY EVENING
WITH CONFIDENCE STILL LOW WITH REGARDS TO CONTINUED CHANCES FOR
THUNDER...ESPECIALLY WITH GUIDANCE SHOWING THIS WEAK INSTABILITY
QUICKLY BEING SHUNTED TO THE SOUTH OF THE CWA. SO HAVE LEFT OUT
ANY MENTION OF THUNDER FOR MONDAY EVENING OVER THE SOUTHEAST THIRD
OF THE CWA...BUT COULD POSSIBLY BE INCLUDED WITH LATER FORECASTS.

RODRIGUEZ

&&

.AVIATION...

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

* GUSTY SOUTH/SOUTHWEST WINDS THIS AFTERNOON.
* SCATTERED SHRA/ISOLATED TSRA MONDAY AFTERNOON. CMS

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

WINDS HAVE TURNED MORE SOUTH/SOUTHWEST WITH SPEEDS IN THE 10-15KT
RANGE. PERIODIC GUSTS INTO THE UPPER TEENS/NEAR 20KTS WILL ALSO BE
POSSIBLE AS THE DRY AIRMASS ALLOWS A BIT DEEPER MIXING WITH
SLIGHTLY HIGHER SPEEDS/GUSTS THROUGH SUNSET. WINDS WILL DIMINISH
UNDER 10KTS THIS EVENING AND TURN MORE SOUTHWESTERLY MONDAY
MORNING...TURNING MORE WESTERLY MONDAY AFTERNOON. SPEEDS WILL
INCREASE BACK INTO THE 10-12KT RANGE MONDAY MORNING AND DEPENDING
ON THE EXTENT OF CLOUD COVER AND PRECIP COVERAGE...SOME GUSTS INTO
THE UPPER TEEN/LOWER 20 KT RANGE WILL BE POSSIBLE.

LOW PRESSURE WILL MOVE ACROSS WESTERN GREAT LAKES...NORTH OF THE
TERMINALS...ON MONDAY. A TRAILING COLD FRONT WILL MOVE ACROSS THE
AREA MONDAY AFTERNOON. SHOWERS WILL DEVELOP ALONG AND AHEAD OF
THIS FRONTAL BOUNDARY MONDAY AFTERNOON AND HAVE INCLUDED A TEMPO
FOR SHOWERS IN THE 30 HR ORD TAF. THERE ALSO IS A CHANCE FOR A FEW
THUNDERSTORMS...ESPECIALLY LATER IN THE AFTERNOON WITH THE FRONT.
DECIDED TO LEAVE TSRA OUT OF THIS FORECAST AS THE EXACT TIMING IS
STILL UNCERTAIN AND THE OVERALL DURATION MAY BE JUST AN HOUR OR
TWO. LATER FORECASTS CAN PIN DOWN BETTER TSRA TIMING/COVERAGE. CMS

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

* MEDIUM FOR WINDS THROUGH THE PERIOD.
* MEDIUM FOR SHRA MONDAY AFTERNOON...LOW FOR TSRA. CMS

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

MONDAY NIGHT...CHC OF EVENING SHRA...THEN CLEARING.

TUESDAY AND WEDNESDAY...VFR.

THURSDAY...CHC TSRA.

FRIDAY AND SATURDAY...SLGT CHC SHRA. MAINLY VFR.

RATZER

&&

.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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