Hail and Damaging Winds in Illinois, August 22, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
200 PM CDT WED AUG 22 2001

MODELS FAIRLY CONSISTENT FROM LAST 2 RUNS AND BLENDING ETA/AVN FOR
THIS FORECAST PACKAGE. ETA DOES APPEAR TOO FAR S TONIGHT WITH
FRONTAL BOUNDARY AND RUC HAS BETTER N POSITION SO ADJUSTED ETA FRONT
N BY 100 MILES. FORECAST CHALLENGE IS ADDRESSING SLIGHT RISK OF SVR
STORMS TONIGHT AND IF HEAVY RAIN NEEDED N OF I-70. SVR THUNDERSTORM
WATCH 684 UNTIL 01Z/8 PM FOR N CWFA OR KPIA NWR GROUP. BOUNDARY AND
ASSOCIATED CONVECTION SHIFT INTO AREAS S OF I-70 THU/THU NIGHT. NEXT
IMPULSE FROM UT/AZ BORDER ARRIVES THIS WEEKEND WITH MORE CONVECTION
AND MODELS SLOWER WITH THIS SYSTEM MOVING OUT EARLY NEXT WEEK.

18Z SURFACE ANALYSIS HAS 1010 MB LOW OVER NORTHCENTRAL IA JUST W OF
KEBG WITH A WARM FRONT INTO CENTRAL WI WITH A QUASISTATIONARY
OUTFLOW BOUNDARY OVER FAR N CWFA FROM EARLY MORNING CONVECTION THAT
MOVED ACROSS WI/MI AND N IL. BOUNDARY ACTUALLY STARTING TO LIFT
SLOWLY BACK N OUT OF CWFA LAST HOUR. SCT CONVECTION ALONG THIS
BOUNDARY BY GALESUBURG CLOSER TO SW 40 KT LOW LEVEL JET. COLD FRONT
EXTENDS SW INTO CENTRAL NE AND NW KS. MOSTLY SUNNY SKIES WITH TEMPS
86-94 AND DEWPOINTS IN LOWER 70S WITH HEAT INDICES 95 TO 105. SW
WINDS 10-15 MPH AND GUSTS 15-25 MPH.

CAP SO FAR KEEPING MOST OF CENTRAL IL DRY AS 700 MB TEMPS AT 10C.
SHORT WAVE NEAR NE/IA BORDER MOVING E INTO N IL WITH FRONTAL
BOUNDARY TURNING BACK S ACROSS N IL. GOOD MOISTURE CONVERGENCE ALONG
BOUNDARY WITH SW 30 KT LOW LEVEL JET TO FUEL DEVELOPMENT OF MORE
CONVECTION TONIGHT AND KEEPING LIKELY WORDING THOUGH MAINLY LATE
EVENING AND OVERNIGHT CENTRAL GROUPS. WILL MENTION LOCALLY HEAVY
RAIN N OF I-70 WITH PCPN WATER VALUES APPROACHING 2 INCHES AND
TRAINING EASTBOUND CELLS. PROB40 CHANCE OF CONVECTION AFTER MIDNIGHT
S OF I-70 WHERE CAP IN PLACE AND FURTHER AWAY FROM BOUNDARY. SPC
DAY1 SLIGHT RISK AS FAR S AS BETWEEN I-70 AND I-72. CAPES OF
2500-3500 J/KG AND 35-45 KT DEEP WESTERLY SHEAR TO SUPPORT A FEW
SUPERCELLS WITH LARGE HAIL AND HIGH WINDS MAINLY OVER IA/N IL AND
INTO N CWFA THIS EVENING.

BOUNDARY SHIFTS S INTO S CWFA THU WHERE GOOD CHANCE OF CONVECTION
AND WILL CONTINUE PROB30 CHANCE N WHILE AREAS N OF I-74 APPEAR TO
DRY OUT AS CLOUDS DECREASE WITH CANADIAN HIGH PRESSURE OVER MANITOBA
MOVING INTO ONTARIO AND NOSES INTO NORTHERN IL. STILL HUMID WITH
DEWPOINTS AROUND 70. KEEPING PROB40 CHANCE OF CONVECTION SOUTHERN 6
COUNTIES THU NIGHT. MOST OF CWFA APPEARS TO DRY OUT THU NIGHT/FRI
FROM ENE FLOW FROM CANADIAN HIGH NEAR THE GREAT LAKES BUT STILL
RATHER HUMID WITH DEWPOINTS 65 TO 70. DECENT SHORT WAVE OVER AZ/UT
MOVES INTO THE CENTRAL PLAINS STATES FRI AND AROUND IL THIS WEEKEND.
ETA APPEARS TOO FAST WITH SYSTEM WHILE AVN TOO SLOW. AVN STALLS
DISTURBANCE AND QPF FIELDS OVER IL THRU 12Z/MON. WILL HAVE PROB30
CHANCE OF CONVECTION WEST FRI AFTERNOON AND ACROSS CWFA FRI NIGHT
THRU SUNDAY. PLAN TO KEEP DRY AND LESS HUMID CONDITIONS MON-WED AS
ANOTHER CANADIAN HIGH BUILDS IN FURTHER SOUTH ACROSS THE MIDWEST AND
SEASONABLE TEMPS.

GUIDANCE LOWS TONIGHT AROUND 70 ON TRACK. GUIDANCE HIGHS 80 TO 85 N
AND UPPER 80S SOUTH THU OK. THU NIGHT LOWS AROUND 65 N AND UPPER 60S
SOUTH. FRI HIGHS 80 TO 85 NE AND MID 80S SW.

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

SPI EE 070/086 066/084 067 07643
PIA EE 068/084 064/082 066 07632
DEC EE 070/085 065/084 065 07643
CMI EB 068/084 063/082 063 07642
MTO EB 070/086 066/084 065 07553
LWV EB 072/088 068/087 067 07354

.ILX...NONE.

HUETTL