[LeArc] Forecast Discussion : MLI@ 9/1/02 2:24:25 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 010729
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
225 AM CDT SUN SEP 1 2002

CHANGES UNDERWAY...ESPECIALLY ALOFT...AS PERSISTENT MID/UPPER LEVEL HIGH
IS GETTING BEATEN DOWN BY PARADE OF PACIFIC ENERGY IN STRENGTHENING 
WESTERLY FLOW ACROSS NORTHERN TIER OF STATES. LATEST SURFACE ANALYSIS HASN/T
CHANGED MUCH IN THE LAST FEW DAYS. SURFACE HIGH REMAINS 
ANCHORED OVER GREAT LAKES WITH RIDGING THROUGH THE MID MISSISSIPPI VALLEY. 
COLD FRONT EXTENDS FROM NEAR LAKE WINNEPEG TO LOW PRESSURE OVER CENTRAL SD. 
HAZE AROUND YESTERDAY AND THIS EVENING INDICATIVE OF STAGNANT PATTERN 
AND SIGNALING AIRMASS HAS SINCE PAST IT/S EXPIRATION DATE FOR FRESHNESS.

CONCERNS REVOLVE AROUND LOW PCPN CHCS IN FORECAST FOR TODAY...THEN PCPN CHCS 
TONIGHT INTO TUE WITH COLD FRONT SHIFTING ACROSS REGION. ALSO OF CONCERN 
IS EXTENT OF PRE-FRONTAL WARMING ON MON.

OVERALL...NOT MUCH DIFFERENCE IN MASS FIELDS OF MODELS...ALTHOUGH SIGNIFICANT
DIFFERENCES EXIST WITH RESPECT TO QPF. INCREASING LLVL SOUTHERLY FLOW 
WILL BRING WARMER TEMPS AND MORE HUMID CONDITIONS OVER NEXT COUPLE OF DAYS. 
SHORTWAVE AIDING CONVECTION OVER PORTIONS OF NORTHERN PLAINS AND
UPPER MIDWEST EXPECTED TO LIFT NORTHEAST INTO ONTARIO NEXT 24 TO 36 HRS.
TAIL END THOUGH FROM SOUTHWEST MN INTO NORTHERN NE TO PROPAGATE E/SE
ALONG WITH LLVL CONVERGENCE. LOOKS AS THOUGH ANY DEVELOPMENT ALONG THESE
FEATURES THIS AFTERNOON WILL BE WELL TO THE NORTH/WEST OF CWA. 
NEXT CONCERN IS WITH WEAK ISOLATED CONVECTION DEVELOPING IN SOUTHERN PORTION
OF CWA. WEAK CONVECTION DEVELOPED NEAR AND WEST OF ST. LOUIS METRO
YESTERDAY AFTERNOON WITH WEAK SURFACE LOW AND RIBBON OF SURFACE MOISTURE
FLUX CONVERGENCE. UKMET SUGGESTS THESE WEAK FEATURES TO LIFT A BIT 
FURTHER NORTH TODAY...POSSIBLY AS FAR NORTH AS A UIN-MQB-GBG LINE. AVN SOUNDING
ALSO SUGGESTS CONVECTIVE TEMPS IN MID 80S. SO WITH ALL OF THIS SAID...CAN/T
COMPLETELY RULE OUT ISOLD WEAK CONVECTION THIS AFTERNOON IN FAR SOUTH AND
MAY KEEP TOKEN 20 POP FROM MQB TO EOK. TEMP FORECAST PRETTY SIMPLE OF LATE
WITH GRADUAL MODERATION OF 1-3 DEGS PAST FEW DAYS...SO WILL CONTINUE 
THE TREND WHICH SUGGESTS L/M 80S MOST LOCATIONS. 

TONIGHT...ETA APPEARS TO BE SUFFERING FROM CONVECTIVE FEEDBACK...WHICH THE
TREND THIS SUMMER HAS BEEN FOR AVN TO BE THE CONVECTIVE OVERDRIVE
MODEL. IN ANY EVENT...TAIL OF SHORTWAVE...THETA-E CONVERGENCE AND MOISTURE
ADVECTION SHIFTING TOWARD REGION. VARIOUS PARAMETERS POINT TO 
IA AS POTENTIAL SPAWNING GROUND FOR CONVECTIVE COMPLEX. GUIDANCE HAS POPS IN 
CHANCE CAT WITH BEST CHANCE IN THE NORTH/WEST. HATE TO FLIP FLOP BUT HARD TO
IGNORE HIGH CHANCE POPS IN NORTH/WEST...SO WILL BE NUDGING POPS UP IN 
THESE AREAS.  

MONDAY...MUCH STRONGER SHORTWAVE PROGGED TO RACE EASTWARD ALONG THE 
U.S./CANADIAN LINE. THIS WILL GIVE COLD FRONT PUSH TO THE SE AND 
EVENTUALLY THROUGH THE REGION MON NIGHT AND EARLY TUE. WILL CONTINUE WITH CHC
POPS. EXTENT OF PRE-FRONTAL WARMING TRICKY AS CONVECTIVE DEBRIS TO PLAY
HAVOC WITH POTENTIAL. SURE BET THAT META 2M TEMPS SHOWING 99 DEGS IN 
SOUTHWEST ZONES WON/T VERIFY...LIKEWISE L90S TODAY. META 2M TEMPS HAVE BEEN 
TERRIBLE OF LATE SHOWING OBVIOUS COOL BIAS LAST SEVERAL MORNINGS 
OF ATLEAST 4-7 DEGS AND NOW OFF THE CHARTS WARM BIAS. WHAT HAS WORKED WELL IS 
META 2M MINUS 5-7 DEGS...AND WILL LEAN THIS WAY AS IT MESHES WELL 
WITH MCCLURE METHOD USING LLVL THICKNESS AND VARIOUS THERMAL PARAMETERS. 
  
PCPN THREAT LINGERS TUE MORNING SOUTHERN HALF...THEN SURFACE HIGH BUILDS IN
BRINGING COOL DOWN TO NEAR NORMAL MIDWEEK. 
 

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


M^2