[LeArc] Forecast Discussion : MLI@ 6/18/2003 4:37:47 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 180932
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
400 AM CDT WED JUN 18 2003

08Z MSAS ANALYSIS AND SFC OBS DEPICT WEAK COLD FRONT ROUGHLY FROM 
CENTRAL WI INTO NORTHWEST IA. LACK OF FORCING LIMITING PCPN
TO MAINLY ISOLD-SCTD CONVECTION ATTIM. CANADIAN HIGH PRESSURE CENTERED
NEAR LAKE WINNIPEG WITH RIDGING INTO NORTHERN PLAINS.
WATER VAPOR AND PROFILERS SHOW SHORTWAVE SHEARING SOME WHILE DIVING 
E/SE THROUGH UPPER MIDWEST. 

WEAK FRONTAL ZONE WILL SLIDE SOUTHEAST THROUGH MUCH OF THE CWA 
TODAY...AS SURFACE HIGH BUILDS INTO THE NORTHERN PLAINS AND 
UPPER MIDWEST. INSTABILITY WILL INCREASE ALONG AND AHEAD OF FRONT 
UNDER PARTLY-MOSTLY SUNNY SKIES...WITH CAPES PROGGED IN THE 
RANGE OF 1000-1500 J/KG THIS AFTERNOON AND LI/S -2 TO -4. LIMITING 
FACTORS FOR ANY ORGANIZED SEVERE WX INCLUDE 1) LACK OF SHEAR WITH
WEAK FLOW ALOFT AND 2) LACK OF COHERENT TRIGGER...WITH
WEAK FRONTAL CONVERGENCE AND MAIN SHORTWAVE/FORCING REMAINING TO 
THE NORTH. WITH DEWPTS INCREASING INTO THE 60S AND PW/S CLIMBING
TO BETWEEN 1.5-1.75 INCHES...EXPECT MAIN THREAT TO BE 
LOCALIZED HEAVY RAINFALL WITH FAIRLY SLOW MOVING POST FRONTAL 
MULTICELL TYPE STORMS. GET BENEATH THESE SLOW MOVING STORMS AND IT/S 
NOT OUT OF THE QUESTION TO SEE RAINFALL AMOUNTS EXCEED 1 INCH. 
STILL THOUGH...CAN/T RULE OUT ISOLATED DAMAGING DOWNBURST WINDS.
HIGH WBZ/S SHOULD LIMIT HAIL TO AROUND PEA SIZE AT BEST.
GUIDANCE POPS MAINLY IN CHANCE CAT LOOK REASONABLE...THOUGH WOULD NOT
BE SUPRISED TO SEE SLIGHTLY BETTER COVERAGE OF PCPN IN SOME AREAS. 
TEMPS ARE NEXT CONCERN. BELIEVE WE/LL SEE MORE SUNSHINE THAN 
PREVIOUS FORECAST ADVERTISED...WITH PARTLY-MOSTLY SUNNY SKIES. THIS 
COMBINED WITH LITTLE CHANGE IN TEMPS ALOFT SUPPORT RAISING
TEMPS AT LEAST 1 CAT. LLVL THICKNESS SUPPORTS 85 TO 90 DEGS FROM 
NORTH TO SOUTH...BUT THIS BEING WITH FULL SUNSHINE. STILL...FAVORED 
BLEND OF WARMER FWC AND MET GUIDANCE.

LINGERING CONVECTION THIS EVENING...MAINLY SOUTH OF HIGHWAY 30 TO 
SHIFT SOUTH OF AREA AND WEAKEN BY MIDNIGHT. SUBSIDENCE WITH
CANADIAN HIGH BUILDING IN SHOULD LEAD TO A DECREASE IN 
CLOUDS. STILL HAVE SOME CONCERNS THAT WE COULD SEE LAKE EFFECT CLOUDS
WITH FAVORABLE NORTHEAST FETCH DEVELOPING AFTER MIDNIGHT.
NOT MUCH CONFIDENCE THOUGH ON STRENGTH OF WINDS BEING MUCH ABOVE 10 KTS
TO SUFFICIENTLY ADVECT CLOUDS IN...SO WENT WITH OPTIMISTIC 
SKY TRENDS. TRIMMED BACK GOING MINS BY A FEW DEGS.

MCCLURE


THURSDAY THROUGH SATURDAY...HIGH SETTLES SOUTH FROM WESTERN LAKE 
SUPERIOR THURSDAY MORNING TO OHIO RIVER VALLEY BY SATURDAY NIGHT 
WITH RIDGING ALOFT OVER CENTRAL CONUS. RETURN OF EAST TO NORTHEAST 
LOW LEVEL FLOW WILL KEEP TEMPERATURES AND DEWPOINT VALUES BELOW 
NORMAL AND TRENDED SLIGHTLY ABOVE COOLER MAV GUIDANCE. CHANGE STILL 
ON TRACK FOR SUNDAY THROUGH TUESDAY AS UPPER RIDGE SLIDES EAST WITH 
TROUGH IN WEST PROVIDING PERIODIC SHORTWAVES IN SOUTHWEST FLOW 
ALOFT. RESULTING H85 FLOW WILL MAKE GULF MOISTURE FINALLY AVAILABLE 
FOR BETTER PRECIP CHANCES AND KEPT WITH ONGOING CHANCES IN SUNDAY 
THROUGH TUESDAY TIMEFRAME. LATEST GFS BRINGS IN FIRST SHORTWAVE AND 
SURFACE WARM FRONT AND QPF NORTHWARD INTO CWFA SATURDAY NIGHT. THIS 
IS FASTER THAN PREVIOUS RUNS AND LATEST ECMWF AND WILL THUS HOLD OFF 
MAKING THIS CHANGE UNTIL IT BECOMES MORE CONSISTENT. MAX 
TEMPERATURES THROUGH THIS TIME TO RISE NEAR OR ABOVE NORMAL WITH 
INCREASE IN HUMIDITY TO HOLD NIGHTTIME MINS MUCH WARMER THAN RECENT 
TRENDS.    

SHEETS

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

$$