[LeArc] Forecast Discussion : MLI@ 4/18/2003 3:16:01 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 182013
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
303 PM CDT FRI APR 18 2003

LATEST SFC AND MSAS ANALYSIS INDICATE LARGE PRESSURE FALLS ACRS FAR
EAST NE AND SOUTHWEST IA...WITH TIGHTENING GRADIENT. BRISK EAST
SOUTHEAST SFC WINDS NOTED BEING INDUCED BY THESE PROCESSES/
ISALLOBARIC SURGE ACRS SOUTHWEST INTO SOUTH CENTRAL IA...AND MSAS
LOOP INDICATES THEY ARE HEADED THIS WAY. WILL HAVE TO ACCOUNT FOR
BREEZY EVENING CONDITIONS. WARM FRONT TAKING SHAPE ATTM ACRS
NORTHEAST KS...INTO CENTRAL MO.

PARAMETERS COMING TOGETHER TO PRODUCE AN ELEVATED CONVECTION SPAWNING
GROUND OVER EASTERN NE...SOUTHWEST IA...AND INTO NORTHEAST KS THIS
EVENING. OTHER MORE SCATTERED ACTIVITY MAY ALSO INITIATE OVER NORTH
CENTRAL MO. EXPECT THIS ACTIVITY TO EVENTUALLY PROPAGATE EAST AND
NORTHEAST OVERNIGHT ALONG AND NORTH OF THE ABOVE MENTIONED WARM FRONT
AND AFFECT THE CWA...FEEDING ON VEERING 40-50 KT LLJ AND INCREASING
H85 THTA-E ADVECTION. STILL FEEL ACTIVITY WILL TRY AND STRATIFY OUT
INTO RAIN/SOME EMBEDDED THUNDER AS IT MOVES AWAY FROM UPPER WAVE
SUPPORT ACRS WEST IA...AND INTO COOLER MORE STABLE MID LEVELS OVER
EAST IA AND NORTHERN IL. WILL HAVE TO ACCOUNT FOR ELEVATED
RAIN/SHOWERS PUSHING INTO THE CWA ATTM(THAT ETA SAYS ISN'T THERE)
THIS EVENING AS WELL...AND WILL MAKE LAST MINUTE DECISION ON HOW TO
WORD TOGETHER IN 1ST PERIOD EVENING AND LATE EVENING PRECIP ROUNDS.
TEMPS MAY DROP OFF BRIEFLY THIS EVENING FROM CURRENT READINGS...BUT
THEN EXPECT THEM TO STEADY OR SLOWLY RISE AROUND 50/LOWER 50S
OVERNIGHT.

SAT COULD BE AN ACTIVE DAY AS NEXT MAIN SHORT WAVE PROPAGATES UP
THROUGH DIFFLUENT UPPER FLOW AND TAKES DIRECT AIM AT THE LOCAL AREA
BY EARLY AFTERNOON. GENERALLY PREFER GFS-AVN IN TIMING AND PLACEMENT
OF MAIN SFC AND UPPER LEVEL FEATURES THROUGH SUNDAY...WITH REFERENCE
TO LATEST UKMET AS WELL. THESE TWO MODELS SUGGEST ENERGY TRANSFER
TO THE SOUTH AS SFC LOW OVER SOUTHERN PLAINS DEEPENS AND BECOMES
MAIN PLAYER...WITH SECONDARY WARM FRONT SETTING UP JUST SOUTH OF
THE CWA BY MIDDAY. THIS WILL KEEP CWA BATHED IN MORE OF A SOUTHEAST
FLOW...AND WITH EXPECTED LINGERING CONVECTIVE DEBRIS/PRECIP FROM
TONIGHTS ACTIVITY INTO THE MORNING...CWA MAY BE SLOW TO WARM UP TO
LATER AFTERNOON. AS LOW STARTS TO PULL UP...WARM FRONT WILL LOOK TO
PUSH NORTH TO AT LEAST I-80 CORRIDOR BY 00Z. SHORT RANGE MODELS
SUGGEST DEEP LAYER UVV'S OVER THE CWA SAT AFTERNOON AS H7-H4 MB LAYER
THERMAL WIND BRINGS ABOUT GOOD ROUND OF CVA. BUT HOW WARM AND EXTENT
OF SFC DPTS BEING ADVECTED UP THROUGH WARM SECTOR WILL COME TO PLAY
ON EXTENT AND AREAL COVERAGE OF SVR THREAT SAT AFTERNOON AND
EVENING...WITH LINGERING CLOUD COVER AND EFFECT ON POTENTIAL HEATING
STILL AT QUESTION. AM LEANING TO MOSTLY CLOUDY DAY AND SOUTHEAST
FLOW TO PUT HAMPER ON SEVERE POTENTIAL FOR MUCH OF THE CWA.
LATEST INDICATIONS SUGGEST THAT THE SOUTHEAST CWA/WEST CENTRAL IL UP
THOUGH THE I-80 CORRIDOR MAY HAVE BEST SHOT. QUICK LOOK AT BLEP
TECHNIQUE AND FCST SOUNDINGS WITH VERTICALLY UNIFORM WIND DIRECTION
...SUGGESTS THAT IF HIGHS REACH 70 F WITH SFC DPTS TO AROUND 62(CAPES
BREACHING 1K J/KG MARK)...55-60 KT STRAIGHT LINE WIND OR DOWNBURSTS
WILL BE POSSIBLE. JUST THE POSSIBILITY OF SOME MOMENTUM TRANSFER TO
SFC WITH PROGGED 50-60 KT LLJ WILL BE A CONCERN. LARGE HAIL OF
COURSE TO BE ANOTHER BUT SECONDARY THREAT.

AS SFC LOW PULLS UP JUST WEST OF THE CWA SAT NIGHT...ANOTHER BLAST
OF ENERGY AND PROGGED PW'S/WEST GULF FEED SUGGEST LOCALLY HEAVY RAIN
POSSIBLE INTO SUNDAY MORNING. DRY SLOT WILL LOOK TO SWEEP ACRS THE
CWA AROUND WRAPPING UP SYSTEM FOR END OF PRECIP THREAT BY SUNDAY
AFTERNOON...AND INITIATE NEW SEVERE THREAT WELL TO THE EAST AND
SOUTHEAST OF LOCAL AREA OF CONCERN EASTER AFTERNOON. UPDATED HWO
WITH LATEST THINKING WILL BE SENT SOON.

.LONGER RANGE(MON-FRI)...MEDIUM RANGE MODEL ENSEMBLE SUGGESTS CUT-
OFF UPPER LOW JUST NORTH OF THE AREA ON MONDAY TO OPEN UP AND
PROGRESS EAST...AS BLOCKING UPPER RIDGE SHIFTS EAST AND IMPLANTS
ITSELF ACRS THE CENTRAL CONUS. MODELS MAY BE QUICK TO OPEN UP UPPER
LOW...BUT IT SHOULD STILL EVENTUALLY GET BOOTED. UPPER SYSTEM TO
STILL BRING SHOWER THREAT ON MONDAY BEFORE IT DOES LEAVE. LARGE SFC
RIDGE TO DROP ACRS THE UPPER MS RVR VALLEY AND WESTERN GRT LKS FOR
THE MID WEEK PERIOD...KEEPING TEMPS IN THE 50S TO LOW 60S WITH
COOLING EAST AND NORTHEAST SFC FETCH. ECMWF AND UKMET SUGGEST
SOUTHERN STREAM ENERGY TO TRY AND RIDE UNDER UPPER RIDGE AND BRING
ELEVATED/OVER-RUNNING PRECIP OVER LLVL THERMAL GRADIENT AND AFFECT
AT LEAST THE SOUTHERN CWA ON THU AND POSSIBLY LINGER INTO FRI. LOOKS
LIKE BATTLE OF STUBBORN UPPER MS RVR VALLEY ANTICYCLONE...AND HOW
STRONG SOUTHERN STREAM LOW BECOMES FOR EVENTUAL PRECIP PLACEMENT.
WILL KEEP RAIN CHANCE FOR SOUTHERN HALF OF THE CWA LATER THU AND FRI
FOR NOW. WILL UNDERCUT MEX GUIDANCE HIGH TEMPS ACRS THE NORTH FOR
NEXT THU AND FRI WITH STRENGTH OF SFC HIGH IN MIND AND ASSOCIATED
COOLER INFLUX.


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

$$

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