Severe Thunderstorm Warning 199, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
200 PM CDT WED JUN 21 2000

...FORECAST CONCERNS REST WITH PCPN AND SVR WX CHCS THIS WEEKEND...

18Z SFC ANALYSIS SHOWS DEWPOINT FRONTAL BOUNDARY ACROSS CENTRAL
ILLINOIS ALONG I-74...WITH AN AREA OF SHOWERS AND THUNDERSTORMS
MOVING ALONG IT FROM IOWA/N MO FROM MCV/S.

SEVERAL BOUNDARIES HAVE BEEN LEFT BEHIND BY OVERNIGHT AND MORNING
CONVECTION AND THIS WILL CAUSE A CHALLENGING FORECAST FOR THE NEAR
TERM PERIOD. MOST ACTIVE BOUNDARY SET UP ACROSS SOUTHERN IOWA INTO
SE NEBRASKA. CONVECTION HAS BEEN FIRING ON IT...MOVING EAST AND THEN
REDEVELOPING ON BEHIND IT. BOTH THE ETA AND NGM PICK UP ON THIS WITH
HIGH QPF NEXT 24 HRS...BUT SOME CONCERN AS TO HOW FAR SOUTH THIS
AREA OF PCPN WILL MAKE IT. ETA HAS A LOT OF CONVECTIVE FEEDBACK..BUT
HAS A GOOD HANDLE ON POTENTIAL QPF. AVN HAS A FAIRLY GOOD HANDLE ON
THE SYNOPTIC SCALE FEATURES. NGM SEEMS TOO FAR SOUTH AND AGGRESSIVE
WITH THE QPF FIELDS AS WAS THE CASE WITH YESTERDAYS RUN...BUT EVEN
MORE SO WITH THE NEW 12Z RUN TODAY. WILL BLEND THE ETA/AVN TOGETHER
FOR THIS FORECAST.

SPC HAS WATCHES OUT TO OUR WEST AND NEW MCD PLACES MOST OF THE CWA
WITH GOOD POTENTIAL FOR A WATCH WITH CAPES TO 4000...SFC DEWPOINTS
IN THE MIDDLE 70S...AND AS NOTED ABOVE LOTS OF BOUNDARIES TO WORK
WITH INTO THE OVERNIGHT HOURS.

GIVEN THE RAINS OF THE PAST DAYS AND THE POTENTIAL OVER A EXTENDED
PERIOD OF CONVECTIVE RAINFALL ACROSS THE NORTH AND WEST...
FLOOD/FLASH FLOODING MAY BECOME A BIG CONCERN. HIGH PWAT/S IN PLACE
ALREADY AND RECENT RAINFALLS HAVE LOWERED FFG/S N OF I-70 AS LOW AS
1 TO 2 INCHES IN 1 TO 3 HRS RESPECTIVELY. FLASH FLOOD WATCHES
ALREADY POSTED THROUGH TONIGHT NW OF CWA. AFTER FURTHER DISCUSSION
WITH LSX AND WITH HPC HAVING THE AREA OUTLINED AS WELL...WILL HOIST
FFA FOR TONIGHT AND EARLY SATURDAY ALONG AND WEST OF I-55. BEST RISK
OF HVY RAIN WILL LIKELY BE ACROSS THE NORTH...BUT TOO CLOSE TO CALL.
WILL LEAVE OVERNIGHT CREW TO DECIDE ON EXTENDING.

THE FRONT WILL CONTINUE TO HANG AROUND THE AREA FOR THE NEXT COUPLE
DAYS...BRINGING CHC OF AFTN/EVE STORMS EACH DAY. SPC DAY 2 OUTLOOK
HAS SLGT RISK FOR THE WESTERN CWA. WITH NO OVERALL CHANGE IN THE
WEATHER PATTERN/AIR MASS FROM TODAY...SEE NO REASON TO DISAGREE. BEST
CHCS OF ACTIVITY SHOULD REMAIN ALONG AND N OF THE FRONT ACROSS IOWA
INTO N IL. WILL HIT GOOD CHANCE POPS ACROSS THE NORTH AND DECREASE POPS
FROM THERE DURING MAINLY THE AFTN/EVE HRS.

AS FOR TEMPS THROUGH THE PERIOD...WILL LOWER HIGHS SATURDAY CLOSER
TO MOS NUMBERS WITH HIGHS IN THE MIDDLE 80S DUE TO CLOUDS AND PCPN.
OTHERWISE NO CHANGES PLANNED AS FWC/FAN SIMILAR OTHER PERIODS.

IN EXTENDED...LONGWAVE TROUGH PATTERN WILL TAKE HOLD ACROSS THE
REGION INTO THE NEW WORK WEEK WITH WET AND COOLER CONDITIONS.
STRONGEST S/W LOOKS TO MOVE IN FOR WEDNESDAY...BUT BEST DYNAMICS MAY
REMAIN JUST TO THE NORTH AND WEST...SO WILL GO DRY FOR WEDS. WILL
BACK OFF SLIGHTLY ON TEMPS BASED ON CLOUDIER AND COOLER CONDITIONS
THROUGH EFP.

THANKS FOR CORRDINATION FROM PAH...DVN...LSX.

PRELIMINARY CCF FOR COORDINATION PURPOSES ONLY...

SPI TT 070/085 069/086 067 26+66
PIA TT 068/084 067/085 065 26+66
DEC TT 069/086 069/086 067 26+66
CMI TT 068/086 068/086 067 26755
MTO BT 069/087 070/088 068 26445
LWV BT 072/091 072/090 070 26345

.ILX...FLASH FLOOD WATCH TONIGHT AND EARLYx SATURDAY ROUGHLY ALONG
AND WEST OF INTERESTATE 55.

LF/KH