Severe Thunderstorm Warning 55, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
250 PM CDT THU MAY 17 2001

SEVERAL FORECAST CONCERNS FOR THE FORECAST TONIGHT AND FRIDAY.

LATEST SURFACE ANALYSIS INDICATED THE MAIN SYNOPTIC FRONT FROM NRN
WI THRU CENT IA TO A SFC WAVE IN NW MO. A LARGE MCS HAS DEVELOPED IN
NW MO AT THE INTERSECTION OF THE FRONT/SFC WAVE...AN OUTFLOW
BOUNDARY FROM THE CONVECTION THIS MORNING...AND A TROF THAT XTNDS
DOWN INTO THE SRN PLAINS. SATELLITE IMAGES...AS WELL AS MODELS ALL
POINT TO A CONVECTIVELY INDUCED VORT MAX SCENT KS INTO WRN OK. THERE
WAS ALSO A WEAK BOUNDARY BTWN PIA/SPI AND BMI/DEC WHERE SOME
ELEVATED SHWRS HAVE FORMED. 18Z ILX RAOB INDICATED THAT THE
ATMOSPHERE WAS RATHER CAPPED IN THE LOWER LEVELS. THE ATMOSPHERE WAS
UNSTABLE WRT ELEVATED CONVECTION FORCED ABV 850 MB. HOWEVER...SFC
BASED CONVECTION WILL TAKE QUITE A BIT OF FORCING/HEATING TO
OVERCOME THE CAP.

QUESTION FOR TONIGHT/FRIDAY IS THE EFFECT OF THE VARIOUS BOUNDARIES
AND ESPECIALLY THE MCV IN KS AND THE MCS IN NW MO. THE MODELS ARE
QUITE DIFFERENT IN THEIR HANDLING OF THESE FEATURES. THE AVN IS A
BIT QUICKER WITH THE FRONT AND FARTHER NORTH WITH THE REMNANTS OF
THE VORT MAX...WHILE THE ETA IS FARTHER SOUTH AND SLOWER WITH THE
FRONT. THE AVN HAS BEEN MOST CONSISTENT IN THE PAST SEVERAL
RUNS...BUT THE ETA IS CLOSER IN THE 6 HOUR FCST AT 18Z. ALSO NOTED
THAT A SLIGHT SE PUSH OF THE MCS IN NW MO MAY RESULT IN THE HEAVIER
PCPN IN OUR REGION DEVELOPING/TRACKING FARTHER TO THE SOUTH LATE
THIS EVE/OVERNIGHT SIMILAR TO THE ETA.

WILL GO WITH HIGH POPS (80 PERCENT) FOR WHOLE CWA OVERNIGHT AND
MENTION THE PSBLTY OF LOCALLY HEAVY RAIN MAINLY ALONG AND SOUTH OF
THE I-72 CORRIDOR LATE TONIGHT AND SOUTH OF I-70 FRIDAY. WILL ALSO
KEEP CLOUDS AND RAIN IN THE FCST THROUGH THE DAY FRIDAY AS THE SFC
WAVE TRACKS INTO SRN IL.

DRIER AIR WILL MOVE INTO THE REGION FRIDAY NIGHT SO WILL CLEAR THE
SKY AND GO WITH TEMPS A BIT BELOW GUIDANCE. MOSTLY SUNNY CONDITIONS
XPCTD SATURDAY AS HIGH PRESSURE MOVES ACRS IL. WILL NOT MAKE TOO
MANY CHANGES TO THE EXTENDED FCST...KEEPING THE CHC FOR RAIN IN FOR
MONDAY AND TUESDAY. ONLY CHANGE WILL BE TO ADD PCPN FOR LATE SUNDAY
IN WRN HALF OF FORECAST AREA.

COORD WITH LSX.

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

SPI TU 062/073 049/075 053 23860
PIA TU 059/071 048/075 053 23850
DEC TU 062/072 049/075 052 23860
CMI TU 063/072 048/075 052 23871
MTO TU 065/073 048/074 052 23871
LWV TU 068/074 050/078 053 23871

.ILX...NONE.

MILLER