Severe Thunderstorm Warning 15, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
210 AM CST SAT FEB 27 1999

MODELS NOT DOING TOO BAD THROUGH 24 HRS WITH AGAIN ETA THE
FASTEST...ALTHOUGH NGM AND AVN MORE IN LINE WITH ETA AS WAS THE CASE
WITH YSTDYS 12Z RUN. FCST PRBLM TODAY WL BE TIMING OF CDFNT AND
TEMPS.

ANOTHER IN A SERIES OF WEAK SHORTWAVES WAS EVIDENT ON THE WATER
VAPOR LOOP EARLY THIS MORNING ACRS EASTERN MO WITH SVL MORE EMBEDDED
IN BROAD SWLY FLOW ALOFT ACRS OK AND TX. 06Z SFC ANALYSIS INDICATED
WMFNT JUST WEST OF STL WITH QUITE A DEW POINT DISCONTINUITY ALNG THE
BNDRY WITH MID 30 DEW POINTS NORTH AND UPPER 50S SOUTH OF BNDRY.
LAPS ANALYSIS INDICATED TWO AREAS OF MOISTURE CONVERGENCE...ONE ALNG
AND JUST NORTHWEST OF THE ILLINOIS RIVER WITH A SECONDARY AND MORE
IMPRESSIVE MAXIMA ALINGNED ALONG THE NWD ADVANCING WARM FNT ACRS ERN
MO AND SRN IL. ETA SFC PROGS TAKE CDFNT WHICH IS CURRENTLY ACRS WRN
MO INTO CNTRL IL BY 18Z WHICH SEEMS A BIT QUICK. HOWEVER...AS
MENTIONED BEFORE...THE NGM AND AVN MODELS ARE NOT TOO FAR BEHIND ON
THEIR POSITIONS FOR EARLY THIS AFTERNOON.

WL PUSH FRONT THRU THE PIA AND SPI AREAS BETWEEN 18 AND 20Z WITH
AREAS TO THE EAST SEEING FROPA BY THIS EVENING. ETA FCST SNDGS STILL
SHOWING A FAIRLY DECENT CAP IN PLACE...HOWEVER AS MOISTURE
CONVERGENCE INCREASES NEAR SFC BNDRY THIS MRNG INTO EARLY
AFTERNOON... MODIFIED SOUNDINGS INDICATE CAPES OF AROUND 300 J/KG
ACRS OUR FAR CWFA. EARLIER CONVECTION LAST EVENING WAS DRIVEN BY
LIFT ASSOC WITH LEAD SHORT WAVE ALONG WITH FAIRLY IMPRESSIVE LOW LVL
WAA. WARM AXIS AT 850 MB GRDLY SHIFTS TO OUR EAST BY THIS AFTERNOON
WITH FRONTAL LIFT DRIVING THE TSRA INTO THIS EVENING. SPC ADJUSTED
SLGT RISK SWD THIS MRNG WHERE GREATER LIFT AND DEEPER MOISTURE WAS
LOCATED. APPEARS HAIL THE MAIN THREAT WITH THE CONVECTION TODAY...
ESP ACRS OUR SE THIRD.

NEXT PROBLEM WL BE WITH POST FRONTAL PRECIP CHANCES TONIGHT INTO SUN
MRNG AS SRN STREAM SYSTEM CLOSES OFF. 700-300 MB QVCTR CONVERGENCE
FAIRLY IMPRESSIVE ACRS THE SRN HALF OF STATE TNT BEHIND SFC FNT SO
WOULD NOT BE TOO QUICK IN ENDING PRECIP. IN FACT...THICKNESS PROGS
INDICATING LOW AND MID LVL TEMPS GETTING COLD ENOUGH TO SUPPORT A
CHANGEOVR TO SNOW ACRS OUR SOUTH NR CLOSED UPR SYSTEM SUN MRNG.
FURTHER NW...CYCLONIC CURVATURE AND CAA WOULD SUPPORT KEEPING -SHSN
IN FCST. SHOULD HAVE ZONE INPUT IN BY 0830Z.

PIA  54/32  65
SPI  60/34  66
DEC  61/34  66
CMI  63/34  76
LWV  65/36  87

SMITH