[LeArc] Forecast Discussion : MLI@ 7/21/02 3:08:19 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 212008
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
309 PM CDT SUN JUL 21 2002

CHALLENGE THIS PACKAGE CENTERS MAINLY ON FRONTAL PASSAGE LATE 
TONIGHT AND MONDAY AND ASSOCIATED TSRA CHANCES. MAIN MESSAGE FOR 
FIRST PERIOD IS OPPRESSIVE HEAT AND HUMIDITY. 

COLD FRONT AT 18Z ANALYZED FROM WESTERN LAKE SUPERIOR...SOUTH OF 
MSP...THEN SW TO SW NEB. AHEAD OF FRONT SW FLOW UP THROUGH H5 WITH 
CAPPED AIRMASS OVER CWA. TEMPERATURES IN 90S COMBINED WITH DEWPOINTS 
IN 70S CLOSE TO VERIFYING HEAT ADVISORY THIS AFTERNOON AND WILL KEEP 
IT GOING OVERNIGHT AS LITTLE RELIEF EXPECTED UNTIL FROPA. LAST 
NIGHTS LOWS WERE MAINLY IN UPPER 70S AND ON TRACK FOR SIMILAR 
CONDITIONS TONIGHT TO KEEP HEAT INDEX ABOVE 80. DIFFERENCE WILL BE 
ANTICIPATED MCS ALONG ADVANCING FRONT THAT COULD IMPACT LOWS IN RAIN 
COOLED AIR NW OF A LINE FROM CID-DBQ AND WENT CLOSER TO COOLER MAV 
GUIDANCE THERE WITH VALUES CLOSER TO WARMER MET ELSEWHERE. 

FORECAST MODELS HAD SIMILAR HANDLING OF THE UPPER LEVEL LOW IN SRN 
CAN WITH TRAILING TROUGH S INTO HIGH PLAINS PASSING THROUGH REGION 
ON MONDAY. AT SURFACE...NGM WAS OUTLIER WITH MUCH SLOWER TIMING OF 
FRONTAL PASSAGE...WHILE ETA AND AVN MORE SIMILAR. ALL WERE CLOSE 
WITH 18Z POSITION...ALTHOUGH A BIT TOO DEEP WITH SURFACE PRESSURE. 
MSAS 3 HR PRESSURE RISES OVER 2 MB BEHIND FRONT AND AXIS OF 1 MB 
FALLS AHEAD INDICATE FRONT SHOULD BEGIN PROGRESS E-SE AS ADVERTISED. 
WENT ALONG WITH AN ETA/AVN COMPROMISE TIMING OF FRONT THROUGH 
FORECAST AREA. SO FAR...88DS INDICATE CONVECTION LIMITED TO WELL 
BEHIND FRONT THIS AFTERNOON DUE TO STRONG CAP.

LOCAL SEVERE WX ASSESSMENT TECHNIQUE USING RUC40 AND META AROUND 06Z 
TIME FRAME IN NRN CWFA INDICATES CONDITIONS FAVORABLE FOR BROKEN 
SQUALL LINE ALONG FRONT. BOW ECHOES POSSIBLE WITH WINDS UP TO 50 KTS 
AND POSSIBLY HAIL LESS THAN 1.5 WITH EXPECTED 2K J/KG CAPE AND 
MODERATE TO STRONG TRIGGER ALONG FRONT. LOCALLY HEAVY RAIN LOOKS TO 
BE GREATEST RISK WITH HIGH PRECIP H20 AND H85 DEWPOINTS OVER 15C 
ALONG FRONT. WILL KEEP LIKELY POPS ACROSS NW HALF TONIGHT WITH 
BUFFER ZONE OF CHANCE POPS ADDED TO CENTRAL FOR TRICKY TIMING OF 
CONVECTION NEAR PERIOD CHANGE. WITH SLIGHT RISK IN PLACE WILL KEEP 
GOING SEVERE WORDING IN FOR TONIGHT IN NW ZONES. SOME CONCERN FOR 
SEVERE WINDS MONDAY WITH SLOW MOVING FRONT LATE MORNING INTERACTING
WITH OUTFLOW BOUNDARIES IN SOUTH...BUT MAIN THREAT AGAIN HEAVY 
RAIN AND WILL CONTINUE SUCH WORDING WITH LIKELY POPS ENTIRE AREA. 
POST FRONTAL CONVECTION SHOULD CLEAR OUT OF NRN IA ZONES BY 
AFTERNOON AND WILL ADJUST WORDING THERE. 

MONDAY NIGHT THROUGH WEDNESDAY...SURFACE HIGH PRESSURE RIDGE SETTLES 
EAST ACROSS AREA WITH SIGNIFICANT COOL DOWN AND LOWER HUMIDITY. DID 
NOT STRAY TOO FAR FROM GUIDANCE TEMPERATURES...BUT DID RAISE LOWS 
SOME DUE TO ANTICIPATED STUBBORN LOW LEVEL MOISTURE FROM CROP 
EVAPOTRANSPIRATION. BEYOND...MEDIUM RANGE GUIDANCE HAS MORE ACTIVE 
PERIOD THURSDAY THROUGH SUNDAY AS UPPER RIDGE TO WEST FLATTENS AGAIN 
TO BRING WESTERLIES AND IMBEDDED SHORTWAVES ESPECIALLY ACROSS 
NORTHERN CWFA. TOO FAR OUT TO GET DETAILED AND WILL KEEP TSRA 
CHANCES THOUGHOUT WITH REBOUND IN TEMPERATURES. WENT A BIT ABOVE 
GUIDANCE... ESPECIALLY WITH LOWS.

.DVN...
IA...HEAT ADVISORY TONIGHT.
IL...HEAT ADVISORY TONIGHT.
MO...HEAT ADVISORY TONIGHT.

SHEETS