[LeArc] Forecast Discussion : MLI@ 10/22/02 2:12:23 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 221921
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
222 PM CDT TUE OCT 22 2002

AT SURFACE...1042 HIGH WAS CENTERED OVER NORTHEAST MT AT 18Z WITH 
LEADING EDGE OF UNSEASONABLY COLD AIRMASS MARKED BY COLD FRONT FROM 
WEAK LOW OVER WESTERN LAKE ERIE W-SW TO SOUTHWEST MO. LARGE CLEARING 
HAS OCCURRED IN POST FRONTAL SC FIELD OVER MUCH OF CWFA. AT UPPER 
LEVELS...SPLIT FLOW PATTERN PREVAILS WITH POLAR JET STREAM ACROSS MN 
INTO GREAT LAKES AND SOUTHERN STREAM WELL TO OUR SOUTH. MAIN FOCUS 
IS ON TIGHT BAROCLINIC ZONE IN BETWEEN THAT IS MAIN FACTOR IN 
CURRENT WIDESPREAD SNOW ACROSS SD AND MIXED TYPE PRECIPITATION IN 
UPSLOPE H85 WAA AREA OF SOUTH CENTRAL NEB. FORECAST CHALLENGE IS 
TEMPERATURES AND TYPE OF MAINLY LIGHT PRECIPITATION THROUGH THURSDAY 
AS ARCTIC HIGH SETTLES SLOWLY SE AND KEEPS BAROCLINIC ZONE ACROSS 
FORECAST AREA.

MODELS INITIALIZED WELL AND ARE CONSISTENT WITH UPPER LEVEL FEATURES 
THROUGH DAY THREE...KEEPING NEARLY ZONAL FLOW OVER MID MISS VALLEY 
WITH ACTIVE POLAR JET STAYING TO NORTHEAST. AVN INITIALIZED BEST 
WITH LOCATION OF ARCTIC HIGH NEAR KGGW AND THUS FAVOR ITS TENDENCY 
TO KEEP HIGH CENTER OVER DAKOTAS THROUGH WED NIGHT AS OPPOSED TO ETA 
AND NGM PUSHING THE HIGH TOWARD WI MUCH FASTER. THIS RESULTS IN 
SLIGHT INVERTED TROF DEVELOPING WED AND THU WITH H85 FLOW VEERING TO 
THE SE BY LATE IN DAY AS RIDGE BUILDS FROM ND TO CAROLINA COAST. 
RESULTING OVERRUNNING PROCESS WILL CAUSE GRADUAL MID LEVEL 
SATURATION DURING THE DAY. UPPER DIVERGENCE FROM ENTRANCE REGION OF 
NEXT H3 JET ROUNDING NORTHERN STREAM...ALONG WITH WEAK MID LEVEL 
SHORTWAVES WILL PROVIDE ENOUGH LIFT FOR LIGHT PRECIP IN AFTERNOON 
INTO WED NIGHT. WITH INITIALLY DRY LOW LEVEL NE FLOW...IT WILL TAKE 
A WHILE FOR LOW LEVELS TO MOISTEN UP. LOW LEVEL MODEL CONDENSATION 
PRESSURE DEFECITS REMAIN HIGH UNTIL AFTER 12Z THU...SO ANY PRECIP 
WILL BE VERY LIGHT. CRITICAL THICKNESS VALUES SUGGEST SNOW POSSIBLY 
MIXED WITH ANY RAIN DURING WED AFTERNOON IN NW ZONES. WITH AFTERNOON 
TIMING AND CLOUD COVER IN QUESTION...WILL LEAVE OUT MENTION OF SNOW 
AT ONSET AND GO WITH LOW SCATTERED AFTERNOON RAIN POPS. WEDNESDAY 
NIGHT...PRECIPITATION CHANCES INCREASE WITH MIX OF RAIN AND SNOW 
OVER SOUTHERN 2/3RDS AND RAIN SOUTH. WILL KEEP LOW LIKELY CATEGORY 
POPS. THURSDAY HAS BEST CHANCE OF PRECIP IN MORNING WITH EVENT WITH 
LIGHT SNOW OR SNOW MIXED WITH RAIN SUGGESTED BY FORECAST SOUNDINGS 
ACROSS NORTH...THEN LOW LEVELS BEGIN TO DRY OUT IN AFTERNOON. LIKELY 
POPS LOOK JUSTIFIED...BUT WILL HIT MAINLY MORNING WORDING. WITH WARM 
GROUND AND LIGHT PRECIPITATION RATES...DO NOT EXPECT ANY MEASUREABLE 
ACCUMULATIONS. H85 TEMPERATURE GRADIENT THEN RELAXES THURSDAY NIGHT 
THROUGH FRIDAY TO END MEASUREABLE PRECIP THREAT AS RIDGE BREAKS DOWN 
AND TROUGH MOVES INTO NORTHERN PLAINS. 

TEMPERATUREWISE...PROFILES LOOK SIMILAR TO TODAY WITH NE WINDS...BUT 
MUCH LESS SUNSHINE. WILL GO NEAR OR SLIGHTLY ABOVE FWC. FWC 
ESPECIALLY LOOKS TOO COOL WITH WED NIGHT LOWS WITH MID 20S AND 
STAYED CLOSER TO WARMER END OF MOS. WILL ALSO STAY ON COOL SIDE OF 
MOS GUIDANCE FOR HIGHS THURSDAY WITH CLOUDY SKIES AND LIGHT PRECIP. 

A SERIES OF H5 SHORTWAVES PASS TO NORTH FRIDAY AND SATURDAY...BUT 
WILL KEEP MAINLY COOL AND DRY FOR NOW. MEDIUM RANGE GUIDANCE IN 
DISAGREEMENT WITH DETAILS OF UPPER TROUGH SWINGING IN FROM WEST IN 
MONDAY AND TUESDAY TIMEFRAME. ENOUGH AGREEMENT...HOWEVER...TO 
SUPPORT PRECIP BOTH DAYS AND WILL INTRODUCE MIX OF SNOW FOR NORTH ON
TUESDAY.

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

DLS