Severe Thunderstorm Warning 265, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
245 PM CDT TUE AUG 22 2000

18Z SFC CHART SHOWS MAIN SFC FNT FM WRN NEBRASKA THRU SRN IA...INTO
NW TIP OF IL THEN NEWRD TO GREAT LAKES. SECONDARY BOUNDARY FM NRN MO
TO SRN IL WAS THE FOCUS FOR WAA CONVECTION ACRS ILX CWA LAST NIGHT.
MOST OF THE CONVECTIVE ACTIVITY ATTM CONCENTRATED ACRS SRN WI/NRN IL
FM A CLUSTER THAT DEVELOPED IN IOWA WITH HELP FM A S/WV THIS
MORNING. THIS EXPECTED TO STAY MAINLY NORTH OF US...BUT NUMEROUS
OUTFLOW BOUNDARIES FM THIS COMPLEX AND LAST NIGHT/S CONVECTION
EXPECTED TO TRIGGER STORMS LATER TODAY. 18Z ILX SOUNDING REVEALS
DECENT CAP PREVENTING FURTHER DEVELOPMENT THUS FAR. ANY HEATING SHLD
EFFECTIVELY BREAK THIS CAP. PROBLEM IS...HEATING HAS BEEN CUT TO A
MINIMUM SO FAR WITH EXTENSIVE CLOUDS ACRS MOST OF CRL IL.

MAIN FCST CHALLENGE RESTS ON TIMING OF FROPA AND THE EFFECTIVE THIS
WL HAVE ON PCPN CHANCES ACRS ILX CWA.

UPR RIDGE CONTINUES TO BE FLATTENED ACRS THE NRN CONUS AS S/WVS FROM
MEAN UPR TROF CONT TO ROTATE ACRS THE TOP. NEXT S/WV APPARENT ON WV
LOOP MOVING THRU SRN ND ATTM. WRLY UPR FLOW AHEAD OF THIS WAVE
BECOMES NWRLY BEHIND. UNTIL WE CAN TAP IN ON THIS NWRLY
FLOW...EXPECT ONLY SLOW SWRD PROGRESSION TO FNT. CONVECTIVE
DEVELOPMENT ALONG THE FNT WL ALSO HELP TO PUSH IT SOUTH.
HOWEVER...ALL MODELS ARE IN AGREEMENT THAT THE FNT WL LINGER ACRS
CRL IL INTO TMRW.

MONITORING SERN IA/NWRN MO FOR POSSIBLE CONVECTIVE DEVELOPENT LATE
THIS AFT/THIS EVE. IF THIS SHLD OCCUR...THIS CONVECTION WLD BE AIDED
OVERNIGHT BY LOW-LVL JET AND WAA OVER WARM FNT AS IT TRACKS EAST
THEN SOUTHEAST INTO SRN IN BY MORN.

ALL THIS SAID...PLAN TO EXTEND MENTION OF PCPN INTO MOSTLY MORN
NORTH...AND DURING DAY WED CRL...INTO EVE SOUTHEAST. THIS WLD COVER
ANY WAA DURING NIGHT AND ANY CONVECTION THAT WLD REFIRE ALONG THE
BOUNDARY IN THE DAYTIME HEATING. ETA SUGGESTS CAPES 3000+ DURING
18Z-00Z TIME FRAME WITH LI/S TO -8. YET TO BE SEEN IF ENOUGH
ATMOSPHERIC RECOVERY TIME WLD BE AVAILABLE BEFORE FROPA TO GENERATE
TSRA...SO WL KEEP POPS IN THE 30-40 RANGE.

BY WED NIGHT/THU TIME FRAME...NWRLY UPR FLOW SETS UP ACRS UPR
MIDWEST. MRF SUGGESTS WEAK S/WVS IN THE NWRLY FLOW MAY BRING LOW
POPS TO IL LATE THIS WEEK AND THIS WEEKEND. HOWEVER...HAVE OPTED TO
KEEP EXTENDED FCST DRY...WITH NUMEROUS UNCERTAINTIES...INCLUDING THE
POSITIONING AND MOVEMENT OF HURRICANE DEBBY.

PRELIMINARY CCF FOR COORDINATION PURPOSES ONLY...

SPI EB 071/085 067/084 066 81642
PIA EB 069/083 064/082 065 81641
DEC EB 070/084 066/083 066 81642
CMI EB 069/083 065/081 064 81642
MTO EB 071/086 067/084 066 81643
LWV EE 072/088 068/085 067 81643

.ILX...NONE.

PLAHMER