Flooding in Illinois, May 1 to 31, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
315 PM CDT MON APR 29 2002

MDLS CONT TO SHOW AN ACTIVE WX PATTERN THRU NEXT 10 DAYS OR SO.  IN
THE SHORTER TERM THE FOCUS TURNS TO THE POTNTL FOR A BIG SVR WX DAY
ON WED.

PERHAPS THE MOST UNCLEAR PART OF THIS FCST IS THE CNVCTV EVOLUTION
TNGT AND ITS IMPACT ON WX TMW.  NRN BNDRY HAS PUSHED SOUTH TO ARND
I-70 AND WNDS IN GNRL HV BCM MORE ELY MAKING THIS NRN BNDRY HARDER
TO DEFINE.  MEANWHILE WRMFNT MARKING THE WARM AND VERY MSTR RICH
UNSTBL AMS IS LCTD FM SC KS ACRS CNTRL AR INTO THE TN VLY.  SVRL WVS
OF ELEVATED TSTRMS HV ALREADY TRAVERSED SRN PTNS OF MO IN RSPNS TO
STG WAA...MCON...AND GOOD ELEVATED INSTABILITY ABV THE FNTL SFC.
THE MDLS CONT TO SUGGEST THAT TNGT THIS WL BE ONE POTNTLY ACTV ZN
WHILE ANOTHER WL FOCUS MORE NWD FM THE KS/NE BRDR ACRS NRN MO INTO
CNTRL IL LTR TNGT.  THESE ZNS WL CONT HV THE HIEST POPS TNGT WITH
LOW POPS INBTWN.  OF CONCERN IS IF AND HOW CONTD DVLPMNT TO THE
SOUTH WL IMPEDE DPR MSTR AND INSTABILITY RETURN ON WED.  THE MDLS
ARE ALL NOW TRENDING TWDS A MORE NLY SOLN WITH THE SFC LOW
TRACK...AND CONVERGING TWDS THE POTNTL FOR A SIG SVR WX OUTBREAK FOR
OUR CWFA.  THE SRN MOST OF THE MDL SOLNS IS THE ETA AND IT HAS BEEN
FOLLOWED FOR THIS FCST CYCLE...TRACKING THE DPNG SFC LOW FM THE MKC
VCNTY AT 18Z TO NR PPQ TO CNTRL IL BY 03Z.  STRENTHENING AND VEERING
LOW LVL WNDS IN RSPNS TO THE SFC LOW WUD ALLOW THIS RICH WRM SECTOR
AMS CURRENTLY ACRS THE SOPLNS AND LWR MS VLY TO SPRD NWD IN ADVANCE
OF THE LOW AS THE WRMFNT LIFTS TO NR AND JUST NORTH OF THE STL VCNTY
BY LATE AFT.  ALL THE MDLS ARE SHWG AN IMPRSV ELEVATED MXD LYR TO
SPRD ENEWD FM THE PLAINS OVR THE WRM SECTOR WITH MID LVL LAPSE RATES
AOA 7.5 DEGC/KM.  THIS RESULTS IN VRY UNSTBL CONDS BY AFT WITH CAPES
INCRSG TO AOA 4000 J/KG AND LIS ARND -10.  IT APPEARS THE COMBO OF
AFT HTG AND LRG SCALE LIFT FM THE APCHG PLAINS SHRTWV TROF SHUD THEN
REDUCE CIN BY MID-AFT AHD OF THE DRYLN IN THE WRM SECTOR AND INVOF
OF THE E/W WRM FNT.  CNVRGNC ALG THESE BNDRYS SHUD THEN BE
SUFFICIENT TO BREAK THE RMNG CAP AND LEAD THE SCT TSTRM DVLPMNT.
GIVEN THE PROGGED DP LYR SHEAR IN EXCESS OF 60KTS AND INSTABILITY
THE CNVCTV MODE CERTAINLY APPEARS TO BE SUPERCELLS.  ETA HODOGRAPHS
SHOW SOME GOOD LOOPING IN THE LWST KM OR SO THEN MORE UNIDIRECTIONAL
FLOW SUGGESTING THE POTNTL FOR SPLITTING.  THIS HAS PONTL TO BE A
BIG OUTBREAK WITH 1KM SRH VALUES SUPPORTING POTNTL FOR TORNADOES.
THE CAVEATS ATTM ARE THE AFOREMENTIONED IMPACT OF THE CNVCTN TNGT TO
THE SOUTH AND ANY ELEVATED ACTVTY WHICH MAY DVLP AFT SUNRISE TMW
WITH THE VERY UNSTBL AIR ABV THE PBL.  THREAT SHUD END DURING THE
EVNG IN THE EAST THEN MUCH COOLER AND DRIER AIR MOVS SEWD ON STG
NWLY WNDS IN THE WAKE OF THE LOW.  A COOL DAY FOR THURS WITH GUSTY
WINDS GOOD CAA AND INSTABILITY CU/WRAP ANRD ST.  SOME MOD ON FRI AFT
A CHILLY START...THEN MSTR RETURN AND THE NEXT SYS FOR THE WKND.
AND THE ACTV PATTERN CONTS INTO NEXT WK.

.STL...NONE
GLASS