Severe Thunderstorm Warning 84, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
210 PM CDT FRI MAY 12 2000

MAIN WEATHER CONCERN OBVIOUSLY ROOTED IN THE SHORT TERM WITH THE
TORNADO WATCH IN EFFECT FOR CENTRAL IL LATE AFTERNOON INTO THE
EVENING. SPECIAL 18Z SOUNDING HERE AT ILX INDICATED ALL INGREDIENTS
COMING TOGETHER WITH MOISTURE/WARM AIR AXIS...VERY HIGH INSTABILITY
WITH LI/S AROUND -9 AND CAPES CLOSE TO 4000...AND PLENTY OF SPEED
SHEAR IN THE LOWEST 6 KM. THE SOUNDING DOES SHOW A MID LEVEL CAP
OVER OUR REGION...WHICH WILL BREAK QUICKLY WHEN AN APPROACHING COLD
FRONT MOVES CLOSER. AT 18Z THE FRONT EXTENDED FROM JUST WEST OF RFD
TO A SURFACE WAVE JUST EAST OF UIN. MODIFYING OUR SOUNDING INDICATES
THAT WHEN THE CAP BREAKS...THE CAPE WILL JUMP TO 4500.

THE COLD FRONT IS FORECAST TO MOVE EAST OF THE IL RIVER BY EARLY THIS
EVENING...APPROACHING ERN IL AROUND MIDNIGHT. THUS THE SEVERE THREAT
AND RAINFALL CAN BE EXPECTED TO CONTINUE IN CENT IL INTO EARLY EVE...
ENDING IN THE SOUTHEAST LATE TONIGHT.

A POSITIVE TILT TROUGH IN THE NRN PLAINS IS EXPECTED TO SWING INTO
THE NRN GREAT LAKES REGION OVERNIGHT...WITH THE TROUGH AXIS MOVING
THROUGH CENT IL SAT MORNING. STRONG LOW LEVEL COLD AIR ADVECTION IS
ANTICIPATED SATURDAY...ALONG WITH INCREASING SURFACE WINDS AS
GRADIENT TIGHTENS BETWEEN LOW PRESSURE IN ERN ONTARIO AND A BUILDING
HIGH IN THE SRN PLAINS. SATURDAY MORNING WILL START OUT SUNNY WITH
SEASONABLE TEMPS...BUT THEN AM EXPECTING COLD AIR STRATOCUMULUS
CLOUDS TO MOVE INTO THE REGION BY AFTERNOON. THIS WILL KEEP
TEMPERATURES ON THE COOL SIDE WITH HIGHS IN THE LOWER TO MIDDLE 60S.
COULD BE A FEW SPRINKLES WITH THE COLD AIR SC CLOUDS...BUT THE BEST
CHANCE OF ANY RAINFALL AT THIS TIME APPEARS TO BE NORTH OF OUR
REGION.

THE SURFACE GRADIENT WILL WEAKEN SATURDAY NIGHT AND THE CLOUDS WILL
MOVE OUT OF THE REGION...RESULTING IN CLEAR AND QUITE COOL
CONDITIONS. MODELS INDICATE THAT 850 MB TEMPS WILL RANGE FROM 0 TO
-3 OVER CENTRAL/SE IL SAT NIGHT. THIS TRANSLATES TO CHILLY LOWS IN
THE UPPER 30S TO LOWER 40S SUNDAY MORNING.

ON SUNDAY THE HIGH PRESSURE CENTER WILL BE IN SRN IL...WHICH WILL
GIVE US LOW LEVEL WINDS FROM THE WEST AND AN INCREASE IN LOW LEVEL
TEMPERATURES.

SPI EA 053/062 040/071 049 23700
PIA EA 051/061 039/071 048 23420
DEC EA 053/063 040/070 049 23800
CMI EA 053/063 040/070 047 23810
MTO EA 054/065 041/071 049 23800
LWV EA 057/067 042A/072 051 23800

.ILX...
IL...NONE.

MILLER