Severe Thunderstorm Warning 268, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
300 AM CDT WED AUG 23 2000

LEANING CLOSEST WITH ETA SOLUTION NEXT 60 HOURS...AS NGM APPEARS TO
BE TOO FAST WITH SOUTHWARD PUSH OF COLD FRONT...AND AVN APPEARS TO
PUT FRONT TOO FAR SOUTH WITH WEAK AIR FLOW. MODELS AGAIN HAVING A
DIFFICULT TIME HANDLING SHORT WAVES EMBEDDED IN NW UPPER LEVEL FLOW
AND ASSOCIATED QPF FIELDS WHICH CONTINUE TO APPEAR TOO WET TODAY.
FORECAST CHALLENGE IS ADDRESSING CONVECTION CHANCES AND TIMING OF
COLD FRONT SAGGING SOUTH THROUGH CENTRAL IL INTO THU.

UPPER LEVEL RIDGE TO RETROGRADE FROM THE OZARKS INTO THE SOUTHERN ROCKIES
LATE THIS WEEK WHILE AN UNSEASONABLE DEEP TROUGH BECOMES ESTABLISHED
OVER THE EASTERN U.S. THIS CARVED OUT BY A PARADE OF SHORT WAVES
FROM THE NORTHERN PLAINS AND SOUTHCENTRAL CANADA. STRONGEST SHORT
WAVE OVER MI AND LOBING INTO CENTRAL IL SETTING OFF SCT CONVECTION
OVER CENTRAL IL EARLY TODAY EAST OF I-55 WITH A FEW STRONG TO EVEN
SVR CELLS NEAR CMI. THIS ACTIVITY WILL DIMINISH THIS MORNING OVER
EAST CWA AS THIS FEATURE PULLS FURTHER AWAY AND SW NOCTURNAL JET
WEAKENS. MENTIONING SCT CONVECTION EAST CWA INTO MID MORNING.
COMPLEX OF STORMS OVER S IA/N MO AND SUPPORTED BY SW LOW LEVEL JET
MOVING E INTO CENTRAL IL THIS MORNING AND SHOULD WEAKEN. BUT ALREADY
NEAR THE MISSISSIPPI RIVER AND WILL MENTION SCT CONVECTION SPI GROUP
THIS MORNING.

EXPECT REDEVELOPMENT OF SCT CONVECTION ACROSS CWA THIS AFTERNOON AS
FRONTAL BOUNDARY DRAPPED FROM A LOW IN SW NE E ACROSS S IA AND FAR N
IL/IN SAGS SLOWLY S TOWARD PIA/BMI BY SUNSET. QUITE UNSTABLE FROM
PIA/BMI S WITH LIFTED INDICES OF MINUS 7-9C AND CAPES 2500-4000 J/KG
PER ETA AND SOME CONVERGENCE ALONG FRONT TO TRY TO OVERCOME CAP. SPC
HAS NO SLIGHT RISK BUT ISOLATED PULSE TYPE SEVERE FROM PIA/BMI S.
PROB40 CHANCE OF THUNDERSTORMS THIS AFTERNOON.

WILL KEEP A PROB30 CHANCE OF CONVECTION EARLY TONIGHT CENTRAL GROUP
AND PROB40 TONIGHT S CWA AS FRONT SAGS S OF LWV BY 12Z/THU AND THEN
REMAINS NEARLY STATIONARY. WSW NOCTURNAL JET TO ALSO INTERACT WITH
FRONT. ETA STILL UNSTABLE FROM ILX S AND SW ON THU WITH LIFTED
INDICES MINUS 7-9C AND CAPES 2000-4000 J/KG. ETA/AVN SHOWING A SHORT
WAVE IN THE NORTHERN PLAINS DAMPENING OUT AS IT MOVES INTO CENTRAL
IL THU AND COULD DEVELOP ISOLATED CONVECTION. WILL ADD PROB30 CHANCE
OF CONVECTION 6 S COUNTIES CLOSEST TO FRONT. BEST CHANCE OF
CONVECTION TO BE SSW OF CWA IN MID MISSISSIPPI VALLEY. PRECIPITABLE
WATER VALUES OF 1.50-2.00 INCHES TODAY RETREAT S OF I-70 THU AND
DEWPOINTS IN LOW-MID 70S SLIP 5 TO 10 DEGREES SO DRYER AIR FILTERING
IN ON ENE FLOW AROUND HIGH MOVING FROM ND TO OVER LAKE MICHIGAN.

WILL BUMP NORTHERN GROUP A CAT WARMER TODAY/TONIGHT WITH HIGHS
AROUND 85 AND LOWS AROUND 65 WITH SLOWER MOVEMENT OF COLD FRONT
INITIALLY. REST OF FORECAST LOOKS ON TRACK INCLUDING DRY AND
SEASONABLE TEMPERATURES THROUGH THIS WEEKEND.

PRELIMINARY CCF FOR COORDINATION PURPOSES ONLY...

SPI EB 087/067 085/065 085 07432
PIA EB 085/065 083/063 083 07421
DEC EB 085/066 083/064 084 07422
CMI EB 084/065 081/062 082 07421
MTO EB 086/067 084/064 084 07432
LWV EE 088/070 087/067 086 07443

.ILX...NONE.

HUETTL

ILZ040>042-047>052-230445-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LINCOLN IL
1113 PM CDT TUE AUG 22 2000

...SEVERE THUNDERSTORM WATCH 703 HAS BEEN CANCELED...

THE SEVERE THUNDERSTORM WATCH FOR SCHUYLER...CASS...MASON...MENARD...
LOGAN...SCOTT...MORGAN...SANGAMON AND CHRISTIAN COUNTIES HAS BEEN
CANCELED.

SHOWERS AND THUNDERSTORMS WILL CONTINUE TO DEVELOP AND MOVE ACROSS
THE AREA OVERNIGHT...BUT REMAIN BELOW SEVERE CRITERIA.

BYRD