Flash Flooding and Hail in Illinois, July 28, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
245 AM CDT SUN JUL 28 2002

AVN SUFFERING FROM CONVECTIVE GRID SCALE FEEDBACK OVER THE OZARKS
AND UPPER MISSISSIPPI VALLEY LATE SUNDAY NIGHT INTO MONDAY MORNING.
OTHERWISE NCEP LEANED WITH AVN MODEL THIS FORECAST CYCLE AND ETA NOT
TOO MUCH DIFFERENT. FORECAST CHALLENGE IS CONVECTION CHANCES THRU
MON AND IF HEAT ADIVSORY NEEDED TODAY.

07Z SURFACE ANALYSIS HAS FRONTAL BOUNDARY OVER FAR SOUTHERN SD EAST
INTO SOUTHERN MN AND CENTRAL SECTIONS OF WI AND LOWER MI. WARM SSW
FLOW ACROSS IL WITH TEMPS UPPER 70S AND LOWER 80S AND DEWPOINTS IN
THE LOW TO MID 70S. NEAREST CONVECTION OVER NW MO WHERE SHORT WAVE
PRESENT. 7 TO 9 KFT CLOUDS DEVELOPING OVER NW CWA SINCE MIDNIGHT.

WILL RECONFIGURE ZONES KEEPING 3 GROUPS...BUT ORIENT FROM NW TO SE.
KEEPING LIKELY CHANCE OF CONVECTION TODAY NW GROUP BY PIA/GBG WITH
PROB50 CENTRAL AND 40 POPS SE THIS AFTERNOON. THIS IN RESPONSE TO
SHORT WAVE MOVING INTO NORTHERN IL AND INTERACTING WITH DEEP LAYER
TROPICAL MOISTURE AND VERY UNSTABLE AIR MASS. CAPES RUNNING 6000
J/KG AT DVN AND ILX AT 00Z...BUT DO HAVE SOME CAP TO OVERCOME WITH
700 MB TEMPS AT 13C AT 00Z. UPPER LEVEL RIDGE LOOSENS ITS GRIP A BIT
TODAY ALLOWING STRONG CAP TO WEAKEN ESPECIALLY NORTH OF I-70. WILL
BUMP HIGHS UP TO AROUND 90 NORTH OF I-70...FOLLOWING WARMEST ETA 2M
TEMPS AS TEMPS CURRENTLY ONLY ABOUT 10 DEGREES FROM 90. THESE TEMPS
COMBINED WITH DEWPOINTS IN THE MID 70S GIVES HEAT INDICES 100 TO 105
AND JUST BELOW HEAT ADVISORY CRITERIA. SAT AFTERNOON HIGHS WERE 88
TO 93 AND HAD HIGHER DEWPOINTS IN THE UPPER 70S WHICH POOLED ALONG
WARM FRONT. BUT WARM FRONT AND ASSOCIATED HIGHER DEWPOINTS N OF I-80.

KEEPING CHANCE OF CONVECTION TONIGHT WITH BEST CHANCE NW GROUP LATE
AS FRONT APPROACHES IL. SPC HAS SLIGHT RISK MOST OF CENTRAL IL THRU
TONIGHT BUT THINK BEST CHANCE FOCUSED NW OF CWA CLOSER TO FRONT.
MODELS STILL SHOW FRONT ADVANCING SE INTO NW CWA MON AFTERNOON AND
THRU SE MON NIGHT EXITING KLWV BY 12Z/TUE AS IT WASHES OUT. BEST
CHANCE OF CONVECTION SHIFTS INTO SE CWA MON EVENING WHILE NW DRIES
OUT. SPC CONTINUES SLIGHT RISK MON AND IN SE MON EVENING AND THINK
THIS WILL BE A BETTER CHANCE FOR SEVERE RISK OVER CENTRAL IL AS
FRONT INTERACTS WITH TROPICAL AIR MASS AND ELONGATED SHORT WAVE
MOVES SE ACROSS IL. TEMPS SLIP A FEW DEGREES MON WITH MORE CLOUDS
AND CONVECTION AROUND AND STILL QUITE HUMID. CHANCE OF CONVECTION
LURKS JUST SOUTH OF CWA TUE WHERE FRONTAL BOUNDARY LINGERS ALONG
WITH MORE HUMID AIR MASS. WOULD NOT BE SURPRISED TO SEE ISOLATED
CONVECTION FAR SOUTHERN 6 COUNTIES TUE WHERE DRIER AIR TAKES LONGER
TO ARRIVE BY TUE NIGHT. TUE HIGHS IN THE UPPER 80S TO NEAR 90.

UPPER LEVEL RIDGE SPRAWLED OUT ACROSS THE CENTRAL AND SOUTHERN
STATES THIS WEEK WHILE WESTERLIES AND ZONAL FLOW ACORSS THE NORTHERN
STATES. RIDGE SHOULD KEEP CENTRAL IL WARM AND DRY MOST OF THE WEEK
AFTER MON BUT LAST IMAGE OF AVN SHOWING FRONT AND QPF APPROACHING IL
THU NIGHT. COULD BE A RISK OF CONVECTION FRI AND MRF SHOWING QPF FRI
OVER CENTRAL IL.

THANKS FOR THE COORDINATION IND AND STL.

...PRELIMINARY CCF FOR COORDINATION PURPOSES...

SPI TT 091/074 087/068 088 07545
PIA TT 089/073 086/067 087 07655
DEC TT 090/073 087/068 088 07545
CMI TT 089/072 086/067 087 07545
MTO TT 090/073 089/069 088 07435
LWV TT 092/073 092/071 090 07435

.ILX...NONE.

KH

ILZ027>031-036>038-040>057-061>063-066>068-071>073-281200-

HAZARDOUS WEATHER OUTLOOK FOR CENTRAL ILLINOIS
NATIONAL WEATHER SERVICE LINCOLN IL
550 AM CDT SUN JUL 28 2002

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
CENTRAL ILLINOIS THROUGH MONDAY.

UPPER LEVEL ENERGY WILL MOVE INTO ILLINOIS FROM THE CENTRAL PLAINS
AS A FRONTAL BOUNDARY MOVES INTO A VERY UNSTABLE TROPICAL AIR MASS
THROUGH MONDAY. THIS WILL GENERATE SCATTERED THUNDERSTORMS ACROSS
CENTRAL ILLINOIS. A FEW OF THESE STORMS COULD BECOME SEVERE WITH
DAMAGING WINDS AND LARGE HAIL. THE BEST CHANCE OF SEVERE STORMS WILL
BE WEST OF I-55 TODAY AND EAST OF I-55 MONDAY AFTERNOON AND EVENING.

HOT AND HUMID WEATHER WILL ALSO PREVAIL THROUGH MONDAY. AFTERNOON
TEMPERATURES REACHING THE LOWER 90S WILL COMBINE WITH HIGH HUMIDITY
TO GENERATE HEAT INDICES OF 100 TO 105 DEGREES ACROSS CENTRAL
ILLINOIS TODAY...AND FROM I-70 SOUTH AGAIN DURING MONDAY AFTERNOON.

KH