[LeArc] Forecast Discussion : MLI@ 10/11/02 2:05:24 AM

[learc@mailman.qth.net]

The following weather message is provided by McDonough County E.S.D.A.


FXUS63 KDVN 110711
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
209 AM CDT FRI OCT 11 2002

TEMPERATURES MAIN FORECAST CHALLENGE TODAY AND SATURDAY AS DRAMATIC 
CHANGE OCCURS WITH PASSAGE OF STRONG CANADIAN COLD FRONT. AT 06Z... 
THE FRONT WAS THROUGH MOST OF MONTANA AND PUSHING INTO NORTHERN WY 
AND WESTERN DAKOTAS. THE UPPER LEVELS...W-SW FLOW PREVAILED OVER CWA 
AHEAD OF LONGWAVE TROUGH THAT 00Z ANALYSIS INDICATED FROM NW 
TERRITORIES INTO NORTHERN CA. 

AS TROUGH APPROACHES TODAY...WARM AIR ADVECTION FROM SURFACE THROUGH 
H85 DEVELOPS WITH SOUTHERLY FLOW. BEST WARMING WILL BE REALIZED IN 
EASTERN IA ZONES WHERE SURFACE WINDS WILL BE MOST SOUTHERLY BY 
AFTERNOON AS TROUGH APPROACHES...WHILE SE COMPONENT ASSOCIATED WITH 
LINGERING ANTICYCLONIC FLOW WILL BE LESS FAVORABLE FURTHER EAST. 
WILL GO NEAR OR ABOVE MET IN WEST AND CLOSER TO COMPROMISE FWC IN 
EAST. MAV HIGHS COOLER THAN THURSDAY MAXES...WHICH IS NOT REALISTIC 
GIVEN MORE FAVORABLE WARMING CONDITIONS TODAY.

FORECAST MODELS IN CLOSE AGREEMENT WITH TIMING OF STRONG COLD FRONT 
ENTERING NE IA ZONES AROUND 12Z SATURDAY...SWIFTLY PASSING EAST AND 
SE OF IL AND MO ZONES BY 18Z. MOS GUIDANCE HIGHS VARY BY AS MUCH 
AS 10 DEGREES...MAINLY BASED ON SLIGHT DIFFERENCES IN FRONTAL TIMING 
DURING DIURNAL PERIOD OF RAPID TEMPERATURE RISE. N CENTRAL IL ZONES 
WILL BE WARMEST WITH ONLY CI IN MORNING TO SUPPORT META 2M 
TEMPERATURES INTO LOWER 70S...WHILE EASTERN IA WILL HAVE FROPA 
SHORTLY AFTER SUNRISE WITH MORNING HIGHS IN GUIDANCE BLEND AREA OF 
MID 50S...THEN FALLING TEMPS THROUGH AFTERNOON. PRECIP THREAT WILL 
BE MAINLY POST FRONTAL WITH DECENT MID LEVEL FORCING AHEAD OF UPPER 
TROUGH...SHOWN BY H5-H7 Q VECTOR CONVERGENCE AND TIME-HEIGHT 
SECTIONS...INDICATING PERIOD OF -RA/-SHRA ABOUT 6 HOURS AFTER FROPA. 
LOOKING AT LAPSE RATES...LIMITED MOISTURE AND CONSIDERING 
UNFAVORABLE DIURNAL FROPA...TSRA THREAT LOOKS MINIMAL AND WILL SCALE 
BACK TO MENTION ONLY IN EAST. WILL RAISE POPS TO LIKELY ACROSS N 
WHERE JET LEVEL DIVERGENCE A LITTLE HIGHER AND KEEP 50 GOING 
ELSEWHERE. LINGERING -RA OR -DZ WILL CONTINUE INTO EVENING IN 
EAST...THEN STRONG ISENTROPIC DOWNGLIDE SHOULD BRING CLEARING AND 
COLD CONDITIONS. WENT WITH COMPROMISE BETWEEN EXTREMES...AS MET AS 
MUCH AS 16 DEG WARMER THAN MAV...AS DO NOT EXPECT MUCH DECOUPLING 
WITH STRONG COLD ADVECTION AND SHOULD LIMIT PLUNGE TO MAINLY 30S. 

FLOW QUICKLY RECOVERS TO NEARLY ZONAL FOR MONDAY AS NEXT TROUGH 
APPROACHES. LATEST GUIDANCE A BIT SLOWER AND WILL REMOVE MONDAY 
PRECIP MENTION. OTHERWISE DO NOT EXPECT ANY MAJOR CHANGES IN 
EXTENDED RANGE GRIDS.   

.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

DLS