[LeArc] Forecast Discussion : MLI@ 9/14/02 3:06:05 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 140811
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
305 AM CDT SAT SEP 14 2002

WATER VAPOR IMAGERY INDICATING TWO MAIN SWIRLING VORT REGIONS THAT
WILL TRY AND COME TOGETHER OVER THE NEXT 12-18 HRS...WITH ONE
VIGOROUS VORT SEEN OVER LK WINNIPEG REGION...AND OTHER PUSHING UP
FROM CENTRAL TO THE NORTHERN PLAINS. AS THIS PROCESS TAKES PLACE
TODAY...PORTION OF PLAINS VORT COMPLEX WILL GET DRAWN OVER THE CWA
THIS AFTERNOON...WITH MAIN POSITIVE OMEGA/CVA PUNCH TAKING PLACE OVER
THE NORTHERN THIRD...TO NORTHERN HALF OF THE CWA ROUGHLY FROM 18Z-
22Z. ALSO SHORT RANGE MODELS...ESPECIALLY ETA...CONTINUE TO DEVELOP
SFC WAVE ALONG FRONT WHICH WOULD ENHANCE LLVL CONVERGENCE AND LIFT
ACRS THIS GENERAL AREA AS WELL. THUS BETTER CHANCE FOR RAINFALL OF
.2-.5 AMOUNTS WOULD LAY OUT ROUGHLY FROM SOUTHWEST OF IOW...TO EAST
OF THE DBQ AREA. BUT LOOKS LIKE BETTER BUOYANCY TO FEED SOME
THUNDERSTORM DEVELOPMENT WILL BE MORE PREVALENT ACRS THE SOUTHEAST
CWA THIS AFTERNOON...WHERE STORMS COULD LEAVE RAINFALL IN THE SAME
AMOUNT RANGE...JUST IN A MUCH MORE SPOTTY AND LOCALIZED FASHION.
STILL INSTABILITY AND MOISTURE INFLUX AND EVENTUAL SATURATION...
SOMEWHAT AT QUESTION FOR ANY KIND OF SUBSTANTIAL PRECIP EVENT AND
THUNDERSTORM GENERATION. FEEL MAINLY A SHOWER EVENT...WITH SOME
EMBEDDED THUNDER.

DRY LLVL SOUTH-SOUTHEAST FEED WILL STILL HAVE TO BE OVERCOME...AND
PRECIP ONSET MAY BE TRICKY TO TIME. POS OMEGAS...ISENTROPIC LIFT AND
SATURATION PARAMETERS SUGGEST FIRST AREA TO EXPERIENCE PRECIP
REACHING THE SFC WILL BE ACRS THE SOUTHWEST CWA(SOUTHEAST
IA/NORTHEAST MO) BY MID MORNING...AND BUILD EAST AND NORTHEAST AS DAY
PROGRESSES. FAR EAST AND NORTHEAST CWA MAY NOT SEE RAINFALL UNTIL
LATE AFTERNOON. AGAIN...ALL IN ALL...FORCING AND SATURATION
PARAMETERS STILL SUGGEST BULK OF PRECIP EVENT TO TAKE PLACE IN
AFTERNOON INTO EARLY EVENING. ANY DELAY IN PRECIP ONSET WILL ALLOW
EAST HALF OF CWA TO REACH WARMER MAV HIGHS...OR EVEN ABOVE THEM A FEW
DEGREES. EVAPORATIVE COOLING AND SOONER ONSET OF LOWER AND THICKER
CLOUD COVER SHOULD TEMPER FAR WEST CWA HIGHS...THUS COULD BE BIG
RANGE OF TEMPS FROM WEST-TO-EAST.

LLVL RHS CLEAR FROM NORTH-NORTHWEST...TO THE SOUTH OVERNIGHT AS LLVL
BAROCLINIC RIBBON ORIENTED IN AN WEST-TO-EAST FASHION...IS SHUNTED TO
THE SOUTH IN RESPONSE TO IN-BUILDING ANTICYCLONE. AS MAIN PRECIP BAND
SWEEPS EAST AND SOUTH OF THE CWA BY 06Z...SOUTHEAST CWA MAY
EXPERIENCE SOME DRIZZLE BEFORE SUBSIDENCE AND DRYING DOWN-SLAPS THE
AREA CLEAR OF THE LLVL GRUNGE. LOOKING AT LATEST MODEL 1000-H85 MB
LMRH RATE OF DRY-OUT FROM NORTH TO SOUTH SAT NIGHT...BULK OF NIGHT TO
REMAIN CLOUDY AND WILL ONLY KEEP LATE NIGHT CLEAR OUT WORDING ACRS
THE NORTHWEST. LINGERING MID LEVEL CLOUDS MAY EVEN LAST INTO MID
SUNDAY MORNING ACRS THE SOUTH. COOLING H9-H85 THERMAL PARAMETERS ON
SUNDAY SUPPORT ONGOING TEMPS IN CURRENT ZONE PACKAGE...EVEN WITH
PLENTY OF INSOLATION. PREVIOUS SHIFT'S CONCERN FOR BREEZY CONDITIONS
ON SUNDAY WOULD MAKE SENSE WITH CAA...LINGERING CYCLONIC FLOW
ALOFT...AND IN-BUILDING SFC HIGH PRESSURE GRADIENT. BUT...MODEL
FORECAST WINDS UP TO H8 MB NOT AT ALL IMPRESSIVE FOR MIX DOWN
POTENTIAL WITH UNIFORM 10 KT NORTHERLY FLOW. WONDER IF MODELS ARE
UNDERDOING WIND POTENTIAL SOMEWHAT AND WILL GO WITH A 10 TO 20 MPH
RANGE FOR NOW. ONGOING PACKAGE GENERALLY LOOKS GOOD.

NO CHANGE TO LONGER RANGE PERIODS.

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

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