[LeArc] Forecast Discussion : MLI@ 10/24/02 1:59:53 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 241908
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
207 PM CDT THU OCT 24 2002

SURFACE HIGH WAS CENTERED NEAR LAKE HURON WITH RIDGE EXTENDING WEST 
INTO DAKOTAS AT 18Z. WEAK INVERTED TROUGH WAS NUDGING NORTH INTO 
RIDGE FROM AR INTO SOUTH CENTRAL IA. AT UPPER LEVELS...SPLIT FLOW 
CONTINUES WITH POLAR JET COMING OUT OF BLOCKING PATTERN IN WESTERN 
CANADA SE INTO GREAT LAKES AND SUBTROPICAL JET ROUNDING BROAD UPPER 
TROUGH AXIS OVER BAJA CA. WATER VAPOR IMAGERY SHOWED A COUPLE 
IMPRESSIVE WAVES ROUNDING WESTERN TROUGH...WITH LEAD WAVE MOVING 
INTO W TEXAS. BAROCLINIC ZONE CONTINUES ALONG EDGE OF ARCTIC 
AIRMASS...FROM TX PANHANDLE THROUGH MID MISSISSIPPI VALLEY. MAIN 
FORECAST CHALLENGE IS POPS TONIGHT THROUGH FRIDAY AS WAVES IN H5 
FLOW SEND OVERRUNNING PRECIPITATION NORTH INTO CWFA. 

NO CONSIDERABLE PROBLEMS NOTED IN MODEL INITILIZATION. MOST 
SIGNIFICANT DIFFERENCE WAS STRENGTH AND TIMING OF SHORTWAVES 
APPROACHING IN SW FLOW TONIGHT. ETA HAD EDGE WITH LEAD STRONGER WAVE 
COMPARED TO SATELLITE TRENDS...BUT ALL HAD SAME IDEA WITH LEAD VORT 
MAX NEAR STL AT 00Z. H7 UPWARD OMEGA DEVELOPS BETWEEN 00Z AND 06Z 
THIS EVENING...THEN MID LEVEL Q-VECTOR CONVERGENCE REMAINS OVER 
AREA...ESPECIALLY SOUTH...THROUGH FRIDAY MORNING AS SEVERAL WAVES 
MOVE THROUGH SW FLOW. WITH DEVELOPING LOW IN W TEXAS...GULF MOISTURE 
BEGINNING TO OPEN UP AND PROFILER NETWORK SHOWING H85 WIND FROM S 
NOW INTO W MO. MODELS SHOW THIS H85 WARM AIR ADVECTION STRENGTHENING 
NORTHWARD INTO IA AND IL BY 00Z AND CONTINUING THROUGH FRIDAY 
MORNING TO PROVIDE DECENT MOISTURE FEED. THUS WIDESPREAD 
PRECIPITATION WILL REDEVELOP TONIGHT AND CATEGORICAL POPS IN ORDER.
PRECIPITATION TYPE NO LONGER IN QUESTION AND WILL HAVE ALL RAIN OR 
DRIZZLE AS CURRENT DEWPOINTS IN UPPER 30S TO LOWER 40S AND LOW LEVEL 
EASTERLY FLOW WILL CONTINUE TOPPED BY ELEVATED WARM ADVECTION. THIS 
WILL ALSO PREVENT MUCH TEMPERATURE DROP OFF...EXCEPT FOR A FEW 
DEGREES TONIGHT AFTER PRECIP BEGINS AND WILL GO ABOVE WARM END OF 
MOS. 

RAIN SHOULD END IN NORTH FRIDAY AFTERNOON...BUT RAIN OR DRIZZLE TO 
LINGER IN SOUTHERN ZONES AS DEFORMATION ZONE FROM SURFACE LOW TO S 
EXTENDS INTO AREA. WILL THUS RAISE POPS TO LIKELY CATEGORY. WITH 
PRECIPITATION...NEAR SATURATED AIMASS AND WEAK SURFACE WINDS...
GUIDANCE TEMPERATURES LOOK OPTIMISTIC AND PREFER COOLER MAV NUMBERS. 
CLOUDS TO LINGER THROUGH FRIDAY NIGHT WITH LINGERING LOW LEVEL 
MOISTURE AND H5 LOW CURRENTLY OVER MT PASSING TO NORTH AS SHORTWAVE.
REBOUNDING HIGH TO WEST AND SUBSIDENCE SHOULD BRING AT LEAST PARTIAL 
CLEARING SATURDAY AND MILDEST DAY IN PACKAGE WITH HIGHS IN 50S.

BEYOND...BASED ON GFS...HAVE REFINED SUNDAY RAIN CHANCES TO LATE DAY 
AS NEXT WAVE EMERGES FROM SW OVER REDEVELOPING BAROCLINIC ZONE 
ACROSS REGION. COULD SEE MIX OF SNOW IN NORTHERN TIER. EXPANDED 
PRECIP CHANCES MONDAY THROUGH WED AS STRONG E-W CANADIAN H5 TROUGH 
SINKS SOUTH WITH IMBEDDED WAVES IN FLOW OVER FORECAST AREA. MRF/GFS 
OMINOUS WITH SIGNIFICANT SNOW POTENTIAL FOR WED AS MAIN TROUGH AXIS 
APPROACHES FROM NORTH. MORE CONFIDENT THAT COLD AIR TO OUR NORTH 
WILL SPILL IN AROUND MID WEEK LOOKING AT MEDIUM RANGE GUIDANCE 
AND INTRODUCED SNOW CHANCES IN NORTH FOR WED AND RAIN/SNOW IN SOUTH 
FOR NOW WITH TIMING IN QUESTION.  

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

DLS