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000
FXUS63 KLOT 210926
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
426 AM CDT TUE MAY 21 2013

.DISCUSSION...
321 AM CDT

TODAY THROUGH TONIGHT...
MAIN CONCERN FOR TODAY REVOLVES AROUND THE POTENTIAL FOR SEVERE
WEATHER...MAINLY ALONG AND EAST OF A PONTIAC TO CHICAGO LINE.

LINE OF SHOWERS AND THUNDERSTORMS FROM EARLY THIS MORNING CONTINUES
TO PUSH EAST...STRETCHING FROM LOWER MICHIGAN SOUTH THROUGH SOUTHERN
IN. THIS AREA OF CONVECTION HAD BROUGHT SEVERE WEATHER TO PORTIONS
OF NORTHERN IL LAST EVENING...ASSOCIATED WITH A TONGUE OF
ANOMALOUSLY HIGH MOISTURE. PWAT VALUES WITHIN THIS CHANNEL OF
MOISTURE HOVERED BETWEEN 1.2-1.6" AS SOME DRYING WAS NOTED ACROSS
NORTHERN MISSOURI/SOUTHERN IOWA IN THE WAKE OF THE EVENINGS
CONVECTION. TEMPS SHOULD HOLD UP EARLY THIS MORNING IN THE MID/UPR
60S. THEN THE FOCUS TURNS TOWARDS TIMING OF CONVECTION AND THE
INTENSIFY...POSSIBLY SEVERE WEATHER AGAIN.

GUIDANCE INDICATES ANOTHER CAP WILL DEVELOP AND HOLD THRU MOST OF
THE MORNING TIMEFRAME...THEN THE QUESTION IS WHEN THIS CAP WILL
DISSOLVE. LCL GUIDANCE SUGGESTS THE MORE FAVORED ZONE FOR THE
STRONGEST INSTABILITY WILL BE ALONG AND EAST OF A PONTIAC TO GARY
LINE...WHERE LAPSE RATES WILL STEEPEN QUICKLY BY MIDDAY/AFTERNOON.
THE OVERALL SYSTEM THAT HAS PRODUCED THE WIDESPREAD SEVERE WEATHER
REMAINS NEGATIVELY TILTED...WHICH THIS TYPE OF A SETUP COUPLED WITH
INSTABILITY AND ABNORMALLY HIGH MOISTURE...HAS A TENDENCY TO LEAD TO
SEVERE WEATHER OCCURRENCE. THE CHALLENGE IS TRYING TO PIN DOWN THE
TIMING/PLACEMENT...AND ONCE AGAIN THE LACK OF A TRIGGER. A WEAK LOBE
OF VORTICITY DOES APPEAR TO BE PROGGED TO SLIDE NORTH THROUGH
SOUTHCENTRAL IL DURING THE AFTN HOURS...WHICH MAY AID IN INITIATION
OF CONVECTION ACROSS THE SOUTHEASTERN CWFA DURING THE AFTN/EVE
HOURS. PROGGED WIND FIELDS ARE MORE UNIFORM...WHICH SHOULD LIMIT THE
HAZARDS TO A WIND/HAIL THREAT. EXPECT ANY CONVECTION TO FORM INTO A
LINE SEGMENTS SHORTLY AFTER GENERATION.

TEMPS WILL BE DIFFICULT TO PINDOWN FOR THIS AFTN AS WELL. GIVEN THE
RECENT RAINFALL...COUPLED WITH SLIGHTLY COOLER AIR ALOFT TO KEEP
TEMPS CLOSER TO THE LOW 80S FOR MUCH OF THE CWFA. THE FAR SOUTHEAST
CWFA MAY TOUCH THE MID 80S.

THE CHANNEL OF MOISTURE WILL CONTINUE TO HOVER ACROSS THE CWFA
THROUGH THE OVERNIGHT HOURS...AS DEW POINTS REMAIN IN THE LOW/MID
60S. HAVE MAINTAINED LIKELY POPS THRU THE OVERNIGHT HOURS...WITH A
CONTINUED THUNDERSTORMS MENTIONED. FEEL THAT AS TIME MOVES FORWARD
THIS WILL BE ABLE TO BE FINE TUNED...AND POSSIBLY LIMIT CONVECTION
TO
THE EASTERN CWFA.

CONFIDENCE IN SEVERE WEATHER INITIATION...LOW/MEDIUM.


WEDNESDAY THROUGH THURSDAY...
500MB TROUGH AXIS FINALLY ARRIVES ACROSS OVERHEAD...HOWEVER REMAINS
IN A NEGATIVELY TILTED STATE. IT APPEARS INSTABILITY WILL BE WAINING
A BIT THROUGHOUT THE DAY...SO HAVE TRIMMED BACK TO A SLIGHT CHC OF
THUNDER. THIS SEEMS REASONABLE GIVEN THE ABUNDANCE OF CLOUDS. TEMPS
WILL BE MUCH COOLER WED...MAINLY IN THE MID 70S. FOR THUR THE 500MB
VORT SLOWS ACROSS THE CWFA...WITH COOLER AIR SLOWLY FILTERING INTO
THE NEAR SFC ENVIRONMENT. WINDS WILL SLOWLY TURN NORTHERLY BEHIND A
FRONTAL BOUNDARY...THEN NORTHEASTERLY EARLY THUR. THIS WILL ALLOW
THE MARINE ENVIRONMENT TO FILTER INTO FAR NORTHEAST IL...KEEPING
TEMPS IN THE UPR 50S THUR. ANTI-CYCLONIC FLOW IS PROGGED TO ARRIVE
ACROSS THE REGION THUR AFTN/EVE...BRINGING AN END TO THE PRECIP.

CONFIDENCE...MEDIUM/HIGH.

FRIDAY THROUGH MONDAY...
ENSEMBLES HAVE CONTINUED TO SUGGEST THE DEPARTING 500MB TROUGH WILL
BUMP UP AGAINST A WESTERN ATLANTIC RIDGE. THIS WILL SLOW THE
EASTWARD PROGRESSION OF THE TROUGH...WHICH SHUD HOLD THE
ANTI-CYCLONIC FLOW ACROSS THE GREAT LAKES REGION THRU FRI NGT WITH
DRY WEATHER. CONSIDERABLE DIFFERENCES ON PRECIP RETURNING TO THE
REGION AMONGST GUIDANCE FOR SAT/SAT NGT...WHICH IS MOST LIKELY A
REFLECTION OF THE SLOWING TREND AND THE MID-LVL RIDGE THAT IS
PROGGED TO BUILD ACROSS THE CENTRAL CONUS INTO THE CANADIAN PRAIRIES
SAT/SUN. MUCH COOLER AIR WILL REMAIN IN PLACE FOR THE START OF THE
EXTENDED...AS TEMPS STRUGGLE TO REACH THE MID/UPR 60S...AND FOR
AREAS ADJACENT TO LAKE MICHIGAN...TEMPS MAY ACTUALLY STRUGGLE TO
REACH THE UPR 50S AS THE COOLER MARINE ENVIRONMENT FLOWS INLAND FROM
A NORTHEAST WIND. THEN TEMPS WILL BEGIN TO WARM FOR THE WEEKEND INTO
THE UPR 60S TO NEAR 70 DEG. THEN BY EARLY NEXT WEEK TEMPS SHOULD
STEADILY WARM INTO THE LOW 70S. HAVE HELD ONTO MENTION OF SLIGHT CHC
POPS IN THE LATER PERIODS OF THE EXTENDED...HOWEVER IT IS POSSIBLE
THAT AS HEIGHTS INCREASE ALOFT THAT DIFFLUENT FLOW WILL INHIBIT THE
PRECIP POTENTIAL. COULD SEE THINGS TRENDING DRIER FOR THE FINAL FEW
PERIODS OF THE EXTENDED.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.AVIATION...

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

* STRONG GUSTY SOUTHWEST WINDS MID MORNING THROUGH AFTERNOON.

* THUNDERSTORMS LIKELY AFTER MIDNIGHT TONIGHT.

ALLSOPP

//DISCUSSION...UPDATED 09Z...
SHOWERS AND THUNDERSTORMS HAVE MOVED OUT OF THE AREA WITH VFR
CONDITIONS EXPECTED THE REST OF THE DAY. AREA OF SHOWERS AND
THUNDERSTORMS OVER CENTRAL IL EXPECTED TO MOVE THROUGH EAST
CENTRAL IL INTO NORTHWEST IN AND STAY SOUTH OF ORD/MDW.

PREVIOUS DISCUSSION 06Z....
MAIN LINE OF THUNDERSTORMS HAS MOVED EAST INTO NORTHWEST INDIANA
AND EAST CENTRAL ILLINOIS. LINGERING SHOWERS BACK THROUGH CENTRAL
ILLINOIS WILL CONTINUE TO SPREAD NNE THROUGH THE CHICAGO METRO
AREA FOR NEXT FEW HOURS WITH SOME EMBEDDED THUNDER. MVFR
CIGS/VSBYS AT TIMES IN HEAVIER SHOWERS BUT EXPECT VFR CONDITIONS
IN BREAKS AND LIGHTER SHOWERS. THIS ENTIRE AREA SHOULD DISSIPATE
AND MOVE OUT OF THE AREA BEFORE DAYBREAK. A SECOND NARROW LINE OF
SHOWERS AND THUNDERSTORMS OVER EASTERN IOWA APPEARS TO BE
WEAKENING AND DON`T EXPECT THIS TO HOLD TOGETHER LONG ENOUGH TO
IMPACT CHICAGO.

WINDS MAY FLOP AROUND A BIT NEXT HOUR OR TWO IN THE WAKE OF THE
MAIN BAND OF THUNDERSTORMS BUT EXPECT PREVAILING WINDS TO BE SOUTH
AROUND 10 KTS THROUGH THE OVERNIGHT HOURS.

IN THE WAKE OF THESE SHOWERS AND THUNDERSTORMS...EXPECT
SUBSIDENCE/DRYING THROUGH THE MORNING. SCATTERED THUNDERSTORMS ARE
NOT OUT OF THE QUESTION DURING THE DAY TUESDAY BUT EXPECT THE
MAIN ACTION TO BE ASSOCIATED WITH A SHORT WAVE TROF MOVING THROUGH
NEW MEXICO...THIS WILL BE ROUNDING THE BASE OF THE LARGE PLAINS
TROF TUESDAY AFTERNOON AND MOVING RAPIDLY NORTHEAST TUESDAY NIGHT.
HAVE MAINTAINED TEMPO THUNDER AFTER 03Z WED.

ALLSOPP

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

* HIGH CONFIDENCE IN WIND FORECAST.

* HIGH CONFIDENCE IN VFR CONDITIONS.

* LOW CONFIDENCE IN ANY THUNDERSTORMS TODAY. MEDIUM CONFIDENCE IN
  THUNDERSTORMS OVERSPREADING THE AREA AFTER MIDNIGHT TONIGHT.

ALLSOPP

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

WEDNESDAY...SCT SHRA/TSRA AND POSSIBLE MVFR CONDITIONS.
THURSDAY...CHC OF SHRA. GUSTY NE WINDS.
FRIDAY...VFR LIKELY.
SATURDAY...SLT CHC OF TSRA.
SUNDAY...CHC OF TSRA.

MTF

&&

.MARINE...
144 AM CDT

LOW PRESSURE WAS OVER THE ND/MN BORDER WITH A WARM FRONT EXTENDING
EAST ACROSS NORTHERN LAKE MICHIGAN EARLY THIS MORNING. THIS
WILL MAINTAIN SOUTH WINDS OVER ALL BUT THE FAR NORTH END OF THE
LAKE TODAY. THE LOW WILL MOVE SLOWLY EAST ACROSS THE LAKE TONIGHT
THROUGH WEDNESDAY. IN THE WAKE OF THE LOW WEDNESDAY NIGHT NORTH
WINDS WILL INCREASE OVER THE LAKE. A PERIOD OF GALE FORCE NORTH
WINDS IS POSSIBLE THURSDAY BEFORE WINDS DIMINISH THURSDAY NIGHT.
HIGH PRESSURE WILL BUILD INTO THE UPPER MISSISSIPPI VALLEY AND
WESTERN LAKES THURSDAY NIGHT AND FRIDAY.

ALLSOPP

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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