Flash Flood and Hail in Illinois, May 8 to 9, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
220 PM CDT WED MAY 8 2002

MAIN FORECAST CONCERNS ARE THE SEVERE WX POTENTIAL IN WRN HALF OF
STATE AND FLOODING POTENTIAL IN CENT/SE SECTIONS.

THE LATEST SFC ANALYSIS INDICATED AN AREA OF LOW PRESSURE IN XTRM NE
NEB...WITH A WARM FRONT ACRS NCENT IA-NRN IL-SE OHIO...AND A COLD
FRONT CURVING FROM THE LOW TO NW KS. THE MODELS ARE A BIT SLOWER
WITH THE MOVEMENT OF THE LOW AND COLD FRONT...BUT OVERALL AGREE
FAIRLY WELL WITH EACH OTHER. THE MAIN DIFFERENCES ARE IN QPF...
WHICH I WILL ADDRESS LATER. THE ATMOSPHERE IS CAPPED IN CENT IL
NOW...BUT ENOUGH BREAKS IN THE CLOUDS AND AMPLE MOISTURE WILL RESULT
IN PLENTY OF INSTABILITY THIS EVE...ESPECIALLY IN THE WRN HALF OF
IL. THE LOW IS XPCTD TO FOLLOW THE PRESSURE FALLS AND TRACK INTO NE
IOWA BY LATE EVENING...WITH THE CDFNT ACRS NCENT MO TO THE OK
PANHANDLE. T-STORMS HAVE ALREADY STARTED BREAKING OUT IN WRN MO AND
WILL BECOME MORE WIDESPREAD FROM WCENT IA-ERN OK THE NEXT FEW HOURS.
BY LATE EVENING THE RESULT SHOULD BE AN EXPANSIVE SQUALL LINE AHEAD
OF THE FRONT...THAT WILL MOVE INTO WCENT IL AFT BY 10 PM OR SO.
DAMAGING WINDS AND HEAVY RAIN ARE PSBL IN LOCATIONS WEST OF I-55
WITH THIS LINE OF STORMS. THE LINE IS FCST TO CONTINUE MOVG EAST
OVERNIGHT...BUT DAMAGING WIND POTENTIAL SHOULD GRDLY DECREASE AS THE
ATMOSPHERE BECOMES A BIT MORE STABLE AND STORMS BECOME LESS SFC
BASED. WILL CONT MENTION OF PSBL SVR STORMS WEST OF A BMI-DEC-
TAYLORVILLE LINE FOR ERLY TONIGHT.

THE NEXT CONCERN IS FOR HEAVY RAIN WITH THIS SYSTEM...AND THE POTENTIAL
FOR FLOODING...ESPECIALLY SOUTH OF I-72. LAST NIGHT/S XPCTD HEAVY
RAFL STAYED OUT OF ALL BUT THE SE COUNTIES (S OF I-70) DUE TO AN MCS
THAT BLOCKED OUR MAIN SOURCE OF MOISTURE AND LIFT IN SRN MO.
TONIGHT/S LINE OF STORMS WILL BE CAPABLE OF PRODUCING HEAVY RAIN
FROM SW MO-ECENT IL AS A SFC WAVE PROGD TO MOVE ALONG THE FRONT IS
INDUCED BY UPR SUPPORT FROM A SRN STREAM SHORTWAVE. THE AVN MODEL
APPRS TO BE OVERDONE IN ITS QPF FCST...BUT THE ETA IS UNDERDONE WITH
A COMPROMISE WEIGHTED TWD THE AVN IN ORDER. WILL CONTINUE TO FOLLOW
LATE MORNING ZFP UPDATE THAT HAS FLOOD WATCH SOUTH OF A BEA-ILX-CMI-
DNV LINE TONIGHT AND ERLY THU.

THE COLD FRONT IS XPCTD TO XTND FROM ABOUT DNV-EFFINGHAM-SE MO BY
DAYBREAK. WILL KEEP LINGERING SHOWERS IN THE FORECAST FOR ERLY
TOMORROW MORNING ROUGHLY ALONG AND EAST OF I-55. STRONG COLD
ADVECTION AND DRYING WILL RESULT IN PARTLY CLOUDY SKIES BY LATE
MORN-ERLY AFTN. TEMPS WILL NOT RECOVER MUCH THURSDAY DUE TO GUSTY
WEST WINDS AND THE COLD ADVECTION. DECREASING WINDS THURSDAY NIGHT
AND A CLEAR SKY WILL RESULT IN COLD TEMPS DIPPING INTO 35-42 RANGE.

HIGH PRESSURE WILL MOVE EAST OF US FRIDAY...SETTING UP A RETURN FLOW
OF MOISTURE BY LATE IN THE DAY. WILL ADD LOW POPS TO THE FCST FOR
FRIDAY NIGHT AS INCREASING LOW LEVEL SOUTHERLY WINDS OVERRUN A
DEVELOPING WARM FRONT. THIS BOUNDARY IS XPCTD TO REMAIN SOUTH OF OUR
REGION THROUGH THE WEEKEND WITH COOL TEMPS AND PERIODS OF RAIN AND
T-STORMS. THE BOUNDARY AND UPR SUPPORT SHOULD MOVE OUT OF THE
MIDWEST BY EARLY MONDAY. HIGH PRESSURE AND WNW UPR FLOW IS XPCTD TO
GIVE US DRY WX AND SEASONABLE TEMPS TUE-WED.

...PRELIMINARY CCF FOR COORDINATION PURPOSES...

SPI BB 053/061 039/067 048 23+30
PIA BB 048/060 036/066 048 23+20
DEC BB 053/061 039/067 048 23+30
CMI BB 054/063 039/067 048 23+40
MTO WB 055/063 040/066 048 23+50
LWV WB 062/068 042/067 050 23+60

.ILX...FLOOD WATCH TONIGHT INTO THURSDAY MORNING SOUTH OF A LINE
FROM BEARDSTOWN-ILX-CMI-DNV ILZ042>057-061>063-066>068-071>073

MILLER