[LeArc] Forecast Discussion : MLI@ 9/2/02 3:12:17 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 022017
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
317 PM CDT MON SEP 2 2002

FOCUS CHALLENGE CENTERS MAINLY ON FIRST PERIOD THUNDERSTORM CHANCES 
WITH COLD FRONTAL PASSAGE...THEN AMOUNT OF COOL DOWN WITH 
TEMPERATURES AS HIGH PRESSURE DROPS DOWN THROUGH MIDWEEK.

AT 19Z THE SURFACE COLD FRONT WAS FROM CENTRAL MN TO ABOUT ALGONA 
IA...TO OMAHA. FRONT HAS SHOWN CONSISTENT EASTWARD PUSH SO FAR TODAY 
AND WITH 3 HR PRESSURE RISES IN 4 MB RANGE IN SD AND NEB...EXPECT IT 
TO CONTINUE TO PROGRESS EASTWARD THIS EVENING. ASSOCIATED MID LEVEL 
SHORTWAVE EXTENDED FROM MAIN VORT EAST OF LAKE WINNEPEG INTO NW IA. 
SEVERAL BANDS OF ELEVATED CONVECTION SEEN ON VISIBLE SATELLITE AND 
FROM ABOUT KDBQ TO KAWG WITH 88D SHOWING SOME OCCASIONAL SHOWERS ON 
NORTHERN END. TSRA COMPLEX THAT MOVED THROUGH EASTERN IA AND NW IL 
OVERNIGHT AND LINGERED UNTIL MIDDAY HAS LAID OUT AN OUTFLOW BOUNDARY 
OBVIOUS ON VISIBLE SATELLITE IN EAST CENTRAL IL CURVING UP TOWARD 
QUAD CITIES...WHERE IT BECOMES WEAKLY EVIDENT ON 88D IMAGERY JUST 
NORTH OF KDVN MOVING NORTH. 

SHORT TERM MODELS IN BASIC AGREEMENT WITH LARGE SCALE FEATURES. ETA 
AND UK HAD BEST 18Z FRONT POSITION AND TRENDED SLOWER THAN AVN WITH 
PASSAGE THROUGH CWA AND GENERALLY FOLLOWED. BEST UPPER FORCING AND 
JET LEVEL DIVERGENCE WELL TO NORTH...BUT SOME INFLUENCE EXTENDS 
SOUTH INTO NORTHERN ZONES BETWEEN 00Z AND 06Z TONIGHT. USUAL POOR 
AGREEMENT WITH QPF FIELDS WITH AVN ONLY MODEL EXTENDING ANY PRECIP 
SOUTH OF FAR NE IA/NW IL. RUC40 QPF TRENDS CLOSEST TO MY THINKING 
WITH THUNDERSTORMS DEVELOPING MID TO LATE AFTERNOON AT PEAK HEATING 
AHEAD OF FRONT AND MOVING THROUGH FORECAST AREA BEFORE MIDNIGHT. 
TEMPERATURES IN 80S TO AROUND 90 AND DEWPOINTS IN 70S HAVE PUSHED 
LAPS SB CAPES INTO 35-40 KJ/JG RANGE WITH WEAKEST CAP OVER NE IA.
SPECIAL 18Z DVN SOUNDING INDICATED CONSIDERABLE 0-3 KM DIRECTIONAL 
SHEAR...WHICH WOULD BE MAXIMIZED ON ANY EXISTING BOUNDARIES. BEST 
SEVERE POTENTIAL WILL BE GREATEST MAINLY NORTH OF HIGHWAY 30 EARLY 
THIS EVENING AND WILL RESTRICT SEVERE WORDING TO THOSE ZONES WITH 
SOME MENTION OF LOCALLY HEAVY RAINFALL WITH HIGH PRECIP H20...BUT 
SHOULD NOT BE A SIGNIFICANT HYDRO EVENT DUE TO FAST FRONTAL MOVEMENT.
STAYED WELL ABOVE GUIDANCE POPS AND PLACED LIKELY IN NORTH...40 
CENTRAL AND 30 PERCENT FOR SOUTH FOR MAINLY EVENING.  

EXPECTING FRONTAL PASSAGE ACROSS MISS RIVER ABOUT 05Z...THEN EAST OF 
CWFA BY 08Z WITH SKIES THEN CLEARING. HIGH PRESSURE OVER HIGH PLAINS 
MOVES INTO WESTERN IA TUESDAY FOR PLEASANT DAY AND GUIDANCE HIGHS IN 
UPPER 70S TO LOWER 80S REASONABLE. RIDGE MOVES OVERHEAD TUESDAY 
NIGHT WITH MODELS APPEARING TO DROP DEWPOINTS AND THUS TEMPERATURES 
TOO LOW...ESPECIALLY IN NORTH. SHOULD STILL GET IN 50S IN MOST AREAS 
WITH CLEAR SKIES...LONGER SEPT NIGHT AND SUBSIDENCE. UPPER RIDGE 
REBOUNDS OVER AREA WED AND THU FOR DRY AND SEASONABLY WARM 
CONDITIONS. SOME HINT OF PRECIP POTENTIAL FOR THURSDAY AS WAVE TOPS 
RIDGE AND WARM AIR ADVECTION PATTERN RETURNS...BUT NOT ENOUGH 
CONFIDENCE TO INCLUDE AT THIS TIME. 

IN EXTENDED...RAISED TEMPERATURES FOR FRIDAY AND SATURDAY AS UPPER 
RIDGE DOMINATES CENTRAL CONUS. PATTERN BEGINS TO BREAK DOWN SUNDAY 
WITH COLD FRONT POSSIBLY BRINGING FROPA IN LATE SAT NIGHT/SUN 
TIMEFRAME AND ADDED TSRA CHANCES TO SUNDAY.       

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

DLS