[LeArc] Forecast Discussion : MLI@ 8/30/02 1:47:25 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 300652
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
150 AM CDT FRI AUG 30 2002

MAIN BAND OF WESTERLIES WELL NORTH OF REGION...WITH TROUGHING OVER WESTERN
STATES AND FROM EASTERN CANADA THROUGH NEW ENGLAND. 
CLOSED MID LEVEL CIRCULATION SEEN ON WATER VAPOR AND UPPER AIR ANALYSIS
OVER MONTANA WITH NEG TILTED SHORTWAVE EJECTING E/NE INTO THE
CENTRAL/NORTHERN PLAINS AIDING CONVECTION IN THE LEE OF THE ROCKIES.
CLOSER TO HOME...BROAD UPPER RIDGE REMAINS IN PLACE WITH 
SURFACE RIDGING AND LLVL EASTERLY FLOW PREVAILING FROM GREAT LAKES TO
SOUTHERN PLAINS. LATEST IR SATELLITE PIC SHOWS CIRRUS DEBRIS FROM
PLAINS CONVECTION SHIFTING ACROSS CENTRAL IOWA. VISIBILITIES AT MOST ASOS
SITES IN CWA STILL AOA 7 MI...THOUGH TEMP/DEWPT SPREADS CLOSING TO WITHIN
2-4 DEGS AND WITH LIGHT WINDS EXPECT TO SEE PATCHY FOG DEVELOPING
AND LIKELY ALREADY HAS IN WAPSI RIVER VALLEY AND OTHER LOW LYING AREAS. 

NOT MANY CONCERNS IN NEAR TERM. MAIN CHALLENGE IS WITH EXTENT OF MODERATION
ON TEMPS AND WHETHER ANY IMPACTS FROM CLOUDS/FOG. LONGER RANGE 
CONCERNS RESIDE WITH FRONTAL PASSAGE EARLY NEXT WEEK AND EXTENT OF PRE-FRONTAL
WARMING...PCPN CHANCES AND THEN AMOUNT OF POST FRONTAL COOLING MIDWEEK. 
 
SOMEWHAT STAGNANT OR BLOCKY PATTERN WE/VE BEEN IN OF LATE SHOWING SIGNS
OF BREAKING DOWN. CLOSED MID LEVEL CIRCULATION OVER MONTANA EXPECTED
TO LIFT E/NE NEXT 48 HOURS. THIS SYSTEM WILL FLATTEN CENTRAL U.S. RIDGE
ALLOWING UPPER FLOW TO BECOME MORE ZONAL OVER THE NORTHERN STATES
AS MAIN WESTERLIES SINK FURTHER SOUTH ALONG THE U.S./CANADIAN BORDER. 
CHANGES REALLY WON/T BE APPARENT UNTIL LATE WEEKEND AND 
ESPECIALLY EARLY NEXT WEEK. UNTIL THEN...STATUS QUO WITH DRY CONDITIONS AND
SLOWLY WARMING TEMPS AS AIRMASS UNDERGOES SOME MODIFICATION.
AS FOR FOG...APPEARS THE TREND LAST COUPLE OF MORNINGS HAS BEEN FOR IT 
TO BE LESS WIDESPREAD AS NOT AS DENSE. MODELS ALSO SHOW FURTHER DRYING IN
LOW LEVELS AND WINDS NOT EXPECTED TO DIE OFF COMPLETELY TONIGHT.
SO WITH ALL BEING SAID...WILL CONTINUE HOLD OFF MENTION OF PATCHY FOG TONIGHT.
ANY FOG WILL LIKELY BE IN THE 2-5 MI RANGE AND HAVE SIGNIFICANCE ONLY TO
AVIATION. 

AVN AND NGM INDICATING SOME UPPER LEVEL DIFFLUENCE OVER THE REGION SAT
AFTERNOON AND EVE. IN FACT...AVN PRINTING OUT VERY LIGHT QPF
OVER NORTHEAST MISSOURI WITH VORT MAX. MOISTURE LACKING AND WITH SURFACE
RIDGING POPS NEXT TO NIL SO AVN DISCARDED. 

ON SUNDAY...REGION CAUGHT IN SQUEEZE PLAY BETWEEN AN APPROACHING COLD FRONT
TO THE NORTHWEST AND A WEAK DISTURBANCE LIFTING NORTH THROUGH THE
OHIO VALLEY. DEEPER MOISTURE EXPECTED TO BE EITHER WEST OR EAST OF THE
REGION. HOWEVER...AVN AND UKMET PROG VORT MAX AND UPPER DIFFLUENCE
ALBEIT WEAK INTO NORTHWEST PORTIONS OF CWA BY 00Z MON.
THIS COUPLED WITH MAX HEATING CAN/T COMPLETELY RULE OUT ISOLATED CONVECTION.
STILL FEW DAYS AWAY AND GIVEN UNCERTAINTIES WITH TIMING/LOCATION
OF VORT MAX WILL LET LATER SHIFTS RE-EVALUATE.

LABOR DAY HAS POTENTIAL TO BE THE WARMEST OF THE NEXT SEVERAL DAYS...WITH
PRE-FRONTAL COMPRESSION. VARIOUS METHODS SUGGESTING POTENTIAL 
FOR U80S TO NEAR 90 DEGS. WILD CARDS WILL BE EXTENT OF CLOUD COVER AND PCPN.
APPEARS FRONTAL PASSAGE IN THE MON EVE-TUE MORNING TIMEFRAME WHERE
BULK OF PCPN EXPECTED...HOWEVER BELIEVE WE WILL SEE QUITE A BIT OF MID/HIGH
LEVEL RELH...WHICH WOULD TEMPER POTENTIAL WARMUP SOME. 
THIS THINKING LOOKS TO HAVE BEEN ALREADY INCORPORATED INTO FORECAST AS MAXES
APPEAR REASONABLE SO WON/T CHANGE. MAY NEED TO BUMP UP THESE UP SHOULD
IT BECOME APPARENT NOT AS MUCH CLOUD COVER WILL AFFECT REGION. 
CHANCE POPS LOOK GOOD AS WELL...THOUGH MAY REMOVE LATE WORDING ESPECIALLY IN
THE WEST WHERE SOME PCPN COULD SNEAK IN DURING THE AFTERNOON. 
PHASING OUT OF SYNC WITH VORT MAX AND SURFACE FRONT FOR NOW...BUT SHOULD THIS
CHANGE THEN POPS WILL NEED TO BE BUMPED UP. SOMETHING FOR LATER SHIFTS
TO MONITOR AS WELL.  

POST FRONTAL AIRMASS LOOKS TO BE PACIFIC IN ORIGIN...THUS NOT MUCH COOLING
...WITH RETURN MAINLY TO NEAR NORMAL.

OVERALL...FORECAST IN DECENT SHAPE WITH ONLY FEW TWEAKS. 
 

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


M^2