Hail and Damaging Winds in Illinois, September 6, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
230 PM CDT THU SEP 6 2001

FORECAST CHALLENGE THIS PERIOD INCLUDES PRECIP CHANCES AHD OF WEAKENING
SHEAR AXIS TNT INTO FRI MRNG...WITH MORE IMPORTANT SHORTWAVE THREATENING
AREA FRI NIGHT INTO SATURDAY.

WATER VAPOR LOOP CLEARLY SHOWING H5 TROF/SHEAR AXIS LIFTING NEWD INTO
THE SRN/CNTRL PLAINS. MOISTURE PLUME HAS SHIFTED EWD ACRS ENTIRE CWA
WITH SCT TSRA DVLPG AHD OF TROF IN INSTABILITY AXIS WHICH SHOWS UP ON
THE LATEST MSAS. 18Z SFC ANALYSIS INDICATING WEAK TROF AXIS FROM NRN
MO INTO SRN ILLLINOIS WITH THE BULK OF THE TSRA ALONG AND NORTHEAST OF
FEATURE. MODELS FAIRLY CONSISTENT IN THEIR HANDLING OF THE H5 SHEAR
AXIS WHICH MOVES ACRS THE CWA THIS EVENING WITH SOME MODEL DIFFERENCES
SHOWING UP AFTER 36 HRS WITH THE STRONGER CLOSED SYSTEM MOVING INTO THE
SRN PLAINS LT FRIDAY. AVN CONTINUES TO BE THE STRONGER OF THE TWO MODELS
WITH THIS FCST RUN AND BASED ON SATELLITE AND UA DATA...FEEL THAT MAY
BE THE WAY TO GO. STILL SOME FAIRLY STRONG WINDS LOCATED ON THE BACKSIDE
OF THE ERN ID TROF WHICH WOULD SEEM TO INDICATE THE DIGGING PROCESS
WL CONTINUE INTO FRIDAY.

SCT TSRA WL CONTINUE ACRS THE CWA THIS EVENING AND NOT REAL CONFIDENT
ON THE TIMING OF PRECIP ENDING AFTER THE TROF MOVES TO OUR EAST LT
TNT SO WL NOT PUT ANY MENTION OF SHOWERS ENDING TNT. WITH THE SHORTWAVE
TO OUR NE ON FRI AND THE MAJOR SHORTWAVE STILL ACRS THE
PLAINS...DONT SEE ANY REAL STRONG FORCING MECHANISMS TO PRODUCE
WIDESPREAD RAINFALL ACRS THE CWA. HOWEVER...BOTH THE ETA AND AVN
PUSHING SOME WEAK OMEGA ACRS THE AREA DURING THE DAY WHICH MAY BE
ALL IT TAKES TO IGNITE STORMS. MODEL GUID SUGGESTING SOME BREAKS IN
THE CLOUD COVER WHICH SHOULD HELP PUSH THE NUMBERS UP CLOSER TO THE
WARMER FWCS. ITS AMAZING THAT THE TIME HEIGHT CROSS SECTIONS
INDICATE SOME DEEP LAYERS OF RH ACRS THE FCST AREA...BUT YET FCST
TEMPS IN THE MID TO UPPER 80S...WHICH THE TWO METER ETA AGREES WITH.

MODELS SUGGEST BEST LAYERED OMEGA AND QG FORCING APPRCH THE CWA SATURDAY
MRNG AS THE CLOSED SRN STREAM SYSTEM OPENS UP AND IS ABSORBED BY THE
NRN STREAM H5 LOW. BY SAT AFTN AND EVENING...REGION IS IN RIGHT ENTRANCE
REGION OF DEPARTING SPEED MAX WHICH SHOULD ENHANCE THE LIFT ACRS THE
AREA AND POTENTIAL FOR HEAVY RAINFALL. DYNAMIC AND SOME FRONTOGENETICAL
FORCING ARND SATURDAY NIGHT TO CONTINUE SHOWERS...AT LEAST INTO THE
EVENING BEFORE MODELS SUGGEST AREA GETS DRY SLOTTED. ON SUNDAY...IMPRESSIVE
COLD ADVECTION ACRS THE CWA WITH 850-700 MB COLD POOL SETTLING ACRS
THE CWA ALONG WITH SOME DECENT DIF POSITIVE VORT ADVECTION...WHICH
SHOULD KEEP AT LEAST SOME LOW POPS GOING DURING THE DAY (WEST DURING
THE MRNG AND MENTION OF POPS ALL DAY EAST). AFTER THAT...UPPER SYSTEM
TO SHIFT NWD INTO CANADA ALLOWING MORE OF A ZONAL FLOW TO PREVAIL ACRS
THE MIDWEST THRU THE FIRST HALF OF NEXT WEEK PRODUCING COOL BUT DRY
CONDITIONS ACRS CNTRL IL. MED RANGE MODELS HINTING AT ANOTHER FRONT
SHIFTING INTO THE MIDWEST ON THU...BUT MOISTURE RIGHT NOW APPEARS TO
BE LIMITED AHD OF BOUNDARY...SO WL NOT INTRODUCE ANY PRECIP CHANCES FOR
THU. THANKS FOR THE COORD DVN.

...PRELIMINARY CCF FOR COORDINATION PURPOSES ONLY...

SPI ET 070/087 070/078 055 44446
PIA TT 069/085 067/077 052 44466
DEC ET 070/087 070/078 055 44446
CMI ET 067/085 067/078 053 44445
MTO ET 069/086 068/081 058 44444
LWV ET 072/087 072/084 061 44344

.ILX...NONE.

SMITH