[LeArc] Forecast Discussion : MLI@ 8/27/02 2:37:43 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 270742
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
242 AM CDT TUE AUG 27 2002

SATELLITE IMAGERY SHOWING CONSIDERABLE CI FROM EARLIER CONVECTION 
FROM MN TO NEB SPILLING OVER MID LEVEL RIDGE INTO CWFA. INITIAL 
CHALLENGE IS POTENTIAL FOR DENSE FOG THROUGH MID MORNING...THEN 
TEMPERATURES THROUGH DAY 3. 

ETA HAD BETTER INITIALIZATION OF H5 FEATURES OVER CENTRAL CONUS 
ESPECIALLY WITH RESPECT TO SHARP DEFORMATION AXIS OVER FAR WESTERN 
IA. ETA ALSO PREFERRED OVER AVN WITH EVOLUTION OF FEATURES COMPARED 
TO SATELLITE AND RADAR AT 06Z...WITH AVN SHOWING CONVECTIVE FEEDBACK 
OVER SD AND ALSO BEING TOO WEAK WITH SHORTWAVE MOVING THROUGH 
CENTRAL WY. HOWEVER...ALL MODELS SHOWED SAME BASIC PICTURE FOR DVN 
CWFA. 00Z ANALYSIS HAD UPPER RIDGE FROM TX TO MN WITH LOW TO 
SOUTHEAST NOW INTO TN VALLEY AND TWO WEAKER UPSTREAM LOWS...ONE OVER 
ID AND OTHER OVER SOUTHERN SASK. AT SURFACE...HIGH WAS CENTERED OVER 
SOUTHERN ONTARIO WITH RESULTING LIGHT EAST TO NE FLOW ON DVN 
SOUNDING EXTENDING TO UP TO NEARLY 300 MB. MODELS SHOW THIS BLOCKING 
PATTERN TO CHANGE LITTLE THROUGH THURSDAY...THEN BEGINNING TO BREAK 
DOWN TOWARD WEEKEND. 

INITIAL CONCERN IS POTENTIAL FOR DENSE FOG TO REDEVELOP THIS 
MORNING. CI REMNANTS FROM EVENING CONVECTION OVER NEB AND MN SEEN 
THINNING AS IT CURVES SE ACROSS IA/IL. TEMP/DEW POINT SPREADS VARY 
SIGNIFICANTLY ACROSS FORECAST AREA AT 07Z WITH NO SIGNIFICANT FOG AT 
METAR SITES YET. HOWEVER...THINNING CI WILL BE KEY. KMCW BRIEFLY 
DROPPED TO 1 MILE AND KPDC AT 1/2 AT 07Z. AM ANTICIPATING ENOUGH 
CI TO HOLD TOGETHER NEXT FEW HOURS TO PREVENT WIDESPREAD DENSE FOG 
SEEN MONDAY AND CURRENT MENTION OF PATCH MORNING FOG SHOULD SUFFICE.

WITH STAGNANT PATTERN...PERSISTENCE WILL DOMINATE TEMPERATURE 
FORECAST. BIGGEST DIFFERENCE FROM MONDAY WILL BE LESS FOG LINGERING 
INTO MID MORNING AND POSSIBLY A LITTLE STRONGER EASTERLY FLOW.  
COULD BE ENOUGH CI FROM UPSTREAM NOCTURNAL CONVECTION TO HAVE 
MINIMAL IMPACT AS WELL. WILL STAY ON COOL SIDE OF GUIDANCE FOR HIGHS 
TODAY...GOING FROM 80 TO 84...WITH SIMILAR HIGHS THROUGH THURSDAY. 
PROLONGED PERIOD OF EASTERLY FLOW SHOULD HELP DEWPOINTS GRADUALLY 
DROP AND THUS ALLOW FOR COOLER OVERNIGHT LOWS AND WILL STAY NEAR OR 
JUST BELOW COOLEST GUIDANCE WITH SOME UPPER 50S. WILL REMOVE POPS 
FOR THURSDAY WITH WEAK UPPER RIDGING STILL TO WEST AND DRY SOUNDING 
EXPECTED FROM PROLONGED FLOW FROM GREAT LAKES. 

BREAKDOWN OF RIDGE STILL LOOKS ON TRACK FOR WEEKEND WITH SHORTWAVE 
IN MORE ZONAL FLOW PASSING TO NORTH TO WARRANT CONTINUING CURRENT 
EXTENDED POPS FOR SATURDAY AND SUNDAY AND DO NOT EXPECT TO MAKE ANY 
CHANGES. 

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

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