Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 251927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
227 PM CDT MON APR 25 2016


.SHORT TERM...
227 PM CDT

THROUGH TUESDAY...

ANOTHER WARM AFTERNOON UNFOLDED ACROSS NORTHERN IL/NORTHWEST IN...AS
TEMPERATURES WERE ABLE TO QUICKLY PUSH INTO THE 70S WITH A FEW
LOCATIONS REACHING 80 DEGREES. THE LOW LEVEL SOUTHERLY FLOW ALSO
HELPED TO ADVECT ADDITIONAL MOISTURE INTO THE AREA WITH DEW POINTS
RISING INTO THE MID/UPR 50S. VISIBLE SATELLITE IMAGERY HAD SHOWN A
CHANNEL OF STRATUS STRETCHING FROM WESTERN WISC DOWN TO CENTRAL
MISSOURI...WITH WATER VAPOR IMAGERY SHOWING A SOME DRIER AIR IN THE
MID LEVELS LIFTING NORTH AHEAD OF THE STRATUS WHICH COULD FURTHER
AGITATE THE MID-LEVELS AFT 21Z. DCAPE THIS HAS BEGUN TO INCREASE AS
A RESULT OF THE DRY AIR ARRIVAL IN THE MID-LVLS ACROSS SOUTHEAST
IOWA/FAR WESTERN ILLINOIS. EFFECTIVE SHEAR CONTINUES TO INCREASE
WITH SOUTHERLY WINDS OVER NORTHERN IL AND WESTERLY FLOW OVER EASTERN
IOWA...ADDS TO THE LOW LEVEL CONVERGENCE/LIFT ZONE AS IT APPROACHES
NORTHERN IL LATER THIS AFTERNOON. CONVECTIVE ALLOWING MODELS
CONTINUE TO POINT TOWARDS INITIALIZATION ACROSS FAR WESTERN
ILLINOIS...THEN EXPECT CONVECTION TO REALIZE THE INSTABILITY THROUGH
THE COLUMN AND QUICKLY ADVANCE AND GROW BY 22-23Z.

ONCE CONVECTION GROWTH AND DEVELOPMENT OCCURS...THE MAIN HAZARDS FOR
SEVERE THREAT WILL CONTINUE TO BE ON DAMAGING WIND AND POSSIBLE
LARGE HAIL. THERE IS SOME INCREASED HELICITY AS THE BETTER
CONVERGENCE ZONE ARRIVES OVER NORTHERN IL THAT AN ISOLATED ROTATING
UPDRAFT COULD OCCUR...HOWEVER THE FOCUS CONTINUES TO BE WITH
DAMAGING WINDS FROM THE INCREASED DCAPE OF NEARLY 1000J/KG AND THE
STEADILY STEEPENING LAPSE RATES FOR LARGE HAIL.

BY 00Z OR SHORTLY AFTER 00Z...CONVECTION SHOULD BE OVER THE CHICAGO
METRO AREA BEGINNING TO TURN SOUTHEAST BASED ON THE VECTORS ALL
POINTING TOWARDS A SOUTHEAST ACROSS NORTHERN IL. THE FORWARD
PROPAGATION OF STORMS SHOULD BE AROUND 30-40KTS...WHICH WILL LIKELY
BRING A QUICK END TO THE CONVECTIVE/SEVERE CONCERNS OVER THE AREA BY
1-2Z. TEMPS TONIGHT WILL HINGE ON THE TIMING OF THE FRONTAL BOUNDARY
THAT IS SLIDING SOUTH ACROSS WISCONSIN BEHIND THE MID-LVL SHORTWAVE.
GUIDANCE HAS BEEN LEANING TOWARDS THIS FEATURE NOT ARRIVING UNTIL
AFTER MIDNIGHT AND PERHAPS JUST PRIOR TO DAYBREAK TUE. THIS WOULD
ALLOW TEMPS TO REMAIN MILD AGAIN TONIGHT IN THE 50S TO PERHAPS MID
40S ACROSS THE NORTHERN PORTIONS OF THE CWFA.

THEN FOR TUE BEHIND THE FRONT WINDS WILL TURN NORTHERLY TO
NORTHEASTERLY AS MUCH COOLER AIR ARRIVES. THERMAL TROUGH PUSHES
TEMPS ALOFT INTO THE 8 TO 11 DEG C...WHICH COUPLED WITH AN EXPECTED
STRATUS LAYER ARRIVING COULD HOLD HIGHS IN THE MID 50S TO MID
60S...THE EXCEPTION WILL BE THE FAR SOUTHERN CWFA WHERE TEMPS REMAIN
MILD ALONG THE BOUNDARY AND COULD WARM INTO THE MID 70S TUE AFTN.
WITH THE ONSHORE FLOW FOR AREAS ADJACENT TO LAKE MICHIGAN TEMPS WILL
STRUGGLE TO WARM BEYOND THE UPPER 40S TO LOW 50S.

BEACHLER

&&

.LONG TERM...
344 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

ANOTHER STRONG NEGATIVELY TILTED SHORTWAVE WILL BRING SEVERE
WEATHER TO THE PLAINS TUESDAY AFTERNOON THEN BEGIN TO WEAKEN AS IT
MOVES TOWARD THE MIDWEST WEDNESDAY. NORTHEAST LOW LEVEL FLOW
SHOULD PROVIDE A STEADY FEED OF DRY AIR WHICH SHOULD HELP DELAY
THE ONSET OF THE PRECIP IN OUR CWA...ESPECIALLY THE FARTHER NORTH
AND EAST YOU GET. HAVE DELAYED THE ONSET OF THE HIGHER POPS FROM
PREVIOUS FORECAST. REALLY NOT LOOKING LIKE MUCH OF A THUNDERSTORM
THREAT THIS FAR NORTH AS WEAK LAPSE AND QUICKLY WEAKENING SYSTEM
KEEPS LOW LEVEL JET AND POTENTIAL FOR LLJ DRIVEN STORMS FAIRLY
LOW. STILL LOOKS LIKE A DECENT RAIN EVENT WEDNESDAY INTO WEDNESDAY
NIGHT. DRIER AND SEASONABLY CHILLY CONDITIONS ARE EXPECTED IN THE
WAKE OF THIS SYSTEM LATER THURSDAY INTO FRIDAY BEFORE WE RINSE AND
REPEAT WITH ANOTHER STRONG NEGATIVELY TILTED CLOSED LOW MOVING
INTO THE PLAINS BEFORE SLOWLY WEAKENING AS IT WOBBLES INTO OUR
AREA NEXT WEEKEND WITH RAIN CHANCES RETURNING. ONCE FRONT MOVES
THROUGH TOMORROW MORNING LOOK FOR CHILLY WINDS OFF THE LAKE TO
LOCK IN FOR THE REST OF THE WEEK AND PROBABLY INTO THE WEEKEND AS
WELL.

IZZI

&&

.AVIATION...
FOR THE 18Z TAFS...

VFR CONDS CONTINUE ACROSS NORTHERN IL/NORTHWEST IN
AIRFIELDS...HOWEVER THE FOCUS REMAINS ON POTENTIAL FOR CONVECTION
TO DEVELOP LATER THIS AFTERNOON THROUGH EARLY EVENING. WINDS WILL
REMAIN BREEZY FROM THE SOUTH TURNING SOUTHWEST AHEAD OF THE
CONVECTION...WITH SPEEDS GENERALLY AROUND 10 TO 15 KT AND GUSTS
BETWEEN 20 TO 25 KT AT TIMES. VISIBLE IMAGERY DOES SHOW A LAYER OF
CUMULUS CLOUDS DEVLEOPING WITH BASES AROUND 5-6KFT AGL...HOWEVER
AS OF MIDDAY THE VERTICAL GROWTH TO THE CUMULUS LAYER DOES NOT
LOOK TOO IMPRESSIVE...WHICH COULD DELAY THE TIMING FOR
SHOWERS/THUNDERSTORMS SLIGHTLY. GUIDANCE CONTINUES TO POINT
TOWARDS 22Z FOR DEVELOPMENT OF SHOWERS/THUNDERSTORMS WESTERN
IL...THEN QUICKLY INCREASEING IN INTENSITY BY 23Z AND APPROACHING
THE CHICAGO METRO TAF SITES. THE CONVECTION SHOULD BE PROGRESSIVE
AND PUSH EAST OF THE ORD/MDW SITES BY 00Z TO PERHAPS JUST AFTER
00Z...WITH CONVECTION ENDING BY 1Z TUE. THE FRONTAL BOUNDARY
REMAINS WELL NORTH/WEST OF THE AIRFIELDS...SO EXPECT ONCE
CONVECTION PUSHES THROUGH THAT WINDS WILL REMAIN WESTERLY. THEN
OVERNIGHT THE FRONTAL BOUNDARY WILL ARRIVE AND QUICKLY FLIP WINDS
TO NORTHWEST THEN NORTHEAST AROUND DAYBREAK TUESDAY. THIS WILL
USHER IN A STRATUS LAYER OF CLOUDS WITH BASES APPROACHING 1500FT
AGL AND PERHAPS A BRIEF PERIOD OF CIGS GOING BELOW 1KFT AGL AFT
DAYBREAK TUE.

BEACHLER

&&

.MARINE...
304 AM CDT

HEADLINES...REPLACED THE GALE WATCH WITH A GALE WARNING FOR LATE
THIS AFTERNOON INTO EARLY TUESDAY MORNING.  ALSO ISSUED A SMALL
CRAFT ADVISORY FOR HAZARDOUS WAVES TUESDAY MORNING INTO WEDNESDAY
EVENING FOR THE IL NSH AND TUESDAY AFTN INTO WEDNESDAY AFTN FOR THE
INDIANA NSH WATERS.

A COLD FRONT IS OVER CENTRAL LAKE MICHIGAN WITH NE WINDS NORTH OF
THE FRONT AND SOUTHEAST WINDS TO THE SOUTH.  WINDS WILL INCREASE TO
GALE FORCE OVER THE NORTHERN END LATE THIS AFTN WHILE WINDS ON THE
SOUTH HALF WILL BECOME SOUTHWEST THIS EVENING. THE FRONT WILL SHIFT
SOUTH AS THE WEAKENING LOW PASSES OVER THE SOUTHERN END OF THE LAKE
TONIGHT.  WINDS BECOME NORTHEAST LEADING TO HAZARDOUS WAVES IN THE
NSH WATERS INTO WEDNESDAY EVENING.  ANOTHER LOW MOVES OVER THE
PLAINS WEDNESDAY AND PASSES SOUTH OF THE LAKE THURSDAY. NORTHEAST TO
EAST WINDS TO 25 KT CONTINUE THROUGH THURSDAY AFTERNOON PROBABLY
LEADING TO ANOTHER PERIOD OF HAZARDOUS WAVES FOR AT LEAST THE IL NSH
WATERS. THE SOUTHERN END OF HIGH PRESSURE CENTERED OVER HUDSON BAY
ROTATES OVER THE LAKE LATE THIS WEEK WITH WEAK NORTH TO NORTHEAST
WINDS. ANOTHER LOW IS PROGGED TO SLOWLY SHIFT EAST FROM THE PLAINS
TO OVER CENTRAL IL AND INDIANA LAKE EARLY NEXT WEEK. THIS WILL
RESULT IN STRENGTHENING NORTHEAST WINDS.

JEE

&&

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

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM TUESDAY TO 4
     PM WEDNESDAY.

&&

$$

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