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000
FXUS63 KILX 151720
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1220 PM CDT WED MAY 15 2013

.DISCUSSION...
ISSUED 1000 AM CDT WED MAY 15 2013

FRONTAL BOUNDARY IS SLOWLY SLIPPING SOUTHWARD ACROSS ILLINOIS...
AND WAS ROUGHLY ALONG A GALESBURG TO KANKAKEE JUST BEFORE 10 AM.
HAVE BEEN SEEING A PERSISTENT BAND OF SHOWERS AND ISOLATED
THUNDERSTORMS...WHICH HAD MAINLY BEEN MOVING EASTWARD ACROSS THE
EXTREME NORTHERN CWA. THIS HAS STARTED SHOWING A BIT OF A
SOUTHWARD PUSH INTO AN AREA WITH A STRONGER CAP...SO AM NOT
EXPECTING IT TO GO MUCH FURTHER SOUTH THIS MORNING. LATEST RAP
MODEL SHOWING THE MORE SIGNIFICANT CAP EROSION HOLDING OFF UNTIL
LATER THIS AFTERNOON...SO HAVE ADJUSTED AFTERNOON POPS TO REFLECT
THE HIGHEST CHANCES AFTER 3 PM. ALSO MADE ADJUSTMENTS TO THE
WINDS...WITH GUSTS OF 20-30 MPH THIS MORNING EXPECTED TO SETTLE
DOWN SOME THIS AFTERNOON.

GEELHART


&&

.AVIATION...
ISSUED 1219 PM CDT WED MAY 15 2013

SHOWERS AND ISOLATED THUNDERSTORMS INCREASING ALONG A FRONTAL
BOUNDARY...WHICH EXTENDS FROM KMQB TO JUST SOUTH OF KIKK AT 17Z.
COVERAGE IS SCATTERED...AND WILL ADDRESS IT WITH VCTS INITIALLY AT
KPIA/KBMI...THEN FURTHER SOUTH MID TO LATE AFTERNOON AS THE
BOUNDARY SLOWLY SINKS. MOST 12Z MODEL GUIDANCE IN AGREEMENT WITH
STALLING THIS BOUNDARY OVER CENTRAL ILLINOIS THIS EVENING...WITH A
NORTHWARD PUSH BEGINNING ON THURSDAY MORNING. SHOWERS/STORMS WILL
REMAIN SCATTERED WITH THIS BOUNDARY AROUND...WITH THE 06-12Z TIME
FRAME MOST LIKELY TO SEE THE BETTER CHANCES OF DRY WEATHER. ENOUGH
CONFIDENCE EXISTS FOR A TEMPO MENTION OF TSRA FROM ABOUT 03-07Z
FROM KSPI EAST TO KCMI.

GEELHART

&&

.PREV DISCUSSION...
ISSUED 326 AM CDT WED MAY 15 2013

SHORT TERM...TODAY THROUGH FRIDAY

COLD FRONT AT 07Z EXTENDED FROM SOUTHWEST WI BACK THROUGH CENTRAL
IA. THIN LINE OF CONVECTION TRYING TO FIRE ALONG A PRE-FRONTAL
TROF NEAR THE I-80 CORRIDOR CURRENTLY. HI-RES SHORT RANGE MODELS
KEEP THIS ACTIVITY NORTH OF THE CWA THROUGH MID MORNING. PRE-FRONTAL
AIRMASS REMAINS QUITE WARM WITH SW WINDS GUSTING OVER 20 MPH AND
MANY LOCATIONS STILL IN THE MID 70S EARLY THIS MORNING. MAIN
FEATURE OF INTEREST TODAY IS THE FRONT WHICH SINKS SOUTH TO NEAR
THE I-72 CORRIDOR THIS EVENING BEFORE STALLING OUT. NOT MUCH FOCUS
FOR ACTIVITY ALONG THE FRONT FOR THE BULK OF THE DAY AS FORCING
AND CONVERGENCE ARE WEAK. FORECAST SOUNDING ALSO SHOW SIGNIFICANT
CAPPING IN PLACE AS WELL AND HAVE LOWERED POPS TO SLGT/LOW CHANCE.
HIGHS REMAIN WELL ABOVE NORMAL AND WITHOUT MUCH OF A COOL PUNCH
BEHIND THE FRONT EVEN THE NORTHERN CWA SHOULD GET INTO THE LOWER
80S...WHILE UPPER 80S POSSIBLE FOR THE SOUTH. BY LATE AFTERNOON
AND ESPECIALLY AFTER 00Z AREA COMES UNDER BETTER MOISTURE
ADVECTION AS A SOUTHERN STREAM MID LEVEL TROF LIFTS NORTHEAST
TOWARDS THE MID MISSISSIPPI VALLEY. THIS IN CONJUNCTION WITH MID
LEVEL COOLING ERODES CAPPING AND SHOULD ALLOW SCATTERED CONVECTION
TO DEVELOP IN THE VICINITY OF THE BOUNDARY. MODEL DEWPOINTS AROUND
70F APPEAR SEVERAL DEGREES TOO HIGH AND LEAD TO CAPES IN EXCESS OF
3K J/KG. WITH EXPECTED LOW 60S DEWPOINT POOL...CAPES ON THE ORDER
OF 1500 SEEM REASONABLE. WINDS ALOFT ARE WEAK UNDER 25 KTS SO
SHOULDNT BE MUCH STORM ORGANIZATION...BUT WITH THAT INSTABILITY
GUSTY WINDS AND HEAVY DOWNPOURS POSSIBLE ESPECIALLY IF STORMS CAN
GET GOING BEFORE DIURNAL HEATING WANES.

LITTLE CHANGE IN THE PATTERN THROUGH THURSDAY...AS THE QUASI-
STATIONARY FRONT WAVERS OVER THE CWA AND THE WEAKENING TROF LIFTS
THROUGH. SO WILL MAINTAIN HIGH CHANCE TO LIKELY POPS THROUGH
THURSDAY. BY THURSDAY NIGHT THE FRONT FINALLY BEGINS TO LIFT BACK
NORTH AND COULD PUSH INTO NORTHERN IL BY FRIDAY MORNING. BUT TO
KEEP THE POPS PARADE GOING...YET ANOTHER LOW AMPLITUDE MID LEVEL
WAVE SHIFTS INTO MO ON FRIDAY. ASSOCIATED LIFT AND MOISTURE AHEAD
OF THIS FEATURE SHOULD BRING ADDITIONAL CONVECTION TO THE CWA.
SLOW MOVEMENT OF THIS WAVE KEEPS PRECIP CHANCES GOING FRIDAY
NIGHT.

LONG TERM...SATURDAY THROUGH TUESDAY

WEAK MID LEVEL FLOW CAUSES THE TROF TO NEARLY STALL OVER THE LOWER
OHIO VALLEY REGION ON SATURDAY AND THIS WILL LEAD TO A CONTINUED
CHANCE OF SHOWERS/STORMS WITH HIGHEST COVERAGE OVER THE EASTERN
CWA. FINALLY BY SATURDAY NIGHT THIS SYSTEM SHIFTS EAST AND A BRIEF
PERIOD OF UPPER RIDGING BUILDS OVER IL AND WE HAVE A PERIOD
WITHOUT MENTION OF PRECIP. ATTENTION FOR THE LAST HALF OF THE
WEEKEND TURNS TO A MORE SIGNIFICANT TROF DEVELOPING OVER THE
PLAINS. EXTENDED MODELS OFFER DIFFERENT SOLUTIONS OF THE STRENGTH
OF THIS TROF WHICH AFFECTS HOW QUICKLY THE ASSOCIATED COLD FRONT
BRINGS THE NEXT CHANCE OF STORMS TO THE AREA. ECMWF MOST
PROGRESSIVE AND WOULD BRING ACTIVITY IN LATE SUNDAY...WHILE OTHER
GUIDANCE SHOWS THIS HOLDING OFF UNTIL MONDAY. WHILE MANY DETAILS
NEED TO BE WORKED OUT...STRENGTH OF UPPER JET AND INSTABILITY
SUGGEST STRONG OR SEVERE STORMS POSSIBLE FOR THE LOCAL AREA. WILL
NEED TO MAINTAIN HIGH CHANCE POPS SUNDAY NIGHT THROUGH MONDAY
NIGHT TO ACCOUNT FOR TIMING UNCERTAINTY. SLOW MOVEMENT OF UPPER
TROF MAY LEAD TO MORE STORM DEVELOPMENT ON TUESDAY MAINLY OVER THE
EASTERN CWA UNTIL A COLD FRONT FINALLY PUSHES EAST BY AFTERNOON
ACCORDING TO LATEST ECMWF. TEMPS WILL REMAIN WELL ABOVE NORMAL
UNTIL COOLER AIR ASSOCIATED WITH THE TROF MOVES IN FOR LATER
TUESDAY INTO MID-WEEK.

25


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$