[LeArc] Forecast Discussion : MLI@ 8/12/02 2:14:36 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 120714
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
210 AM CDT MON AUG 12 2002

FORECAST REMAINS VERY CHALLENGING WITH VERY DYNAMICAL SYSTEM TO IMPACT
REGION NEXT 24 TO 36 HOURS. 

SYNOPTIC SCALE SHOWS VIGOROUS CLOSED UPPER LOW WEST OF LAKE WINNEPEG 
MOVING EAST AT NEAR 20 KT. AT SURFACE...COLD FRONT EXTENDS FROM
NORTHWEST MN TO LOW PRESSURE SOUTHWEST OF SIOUX FALLS SD...THEN SOUTHWESTWARD
TO NEAR NORTH PLATTE. SEVERAL IMPRESSIVE BOW ECHOES OVER PLAINS AND
MIDWEST WITH LARGE BOW MOVING THROUGH MN AND FAR NORTHERN IA SHOWING SIGNS
OF DECELERATING AND WEAKENING. CLOSER TO HOME...WEAK TROUGH IN
UPPER AIR ANALYSIS FROM SOUTHWEST IA INTO WESTERN MO WITH VORT MAX N/E
OF KC METRO. THIS VORT MAX TRIGGERED SCATTERED CONVECTION ON SUN
AND WILL LOOM LARGE IN CONVECTIVE POTENTIAL NEAR TERM...AS SYSTEM DIGS TO
THE WEST PULLING VORT MAX NORTHWARD INTO REGION. 

A LOT OF CONCERNS...WITH NEAR TERM ISSUES REVOLVING AROUND WHETHER CONVECTION
WILL DEVELOP OVER PORTIONS OF CWA THIS MORNING...THEN IMPACTS
OF CONVECTION AND DEBRIS ON TEMPS AND SEVERE POTENTIAL. HEAVY RAIN POTENTIAL
OF CONCERN NEXT 24+ HOURS...THEN FOCUS SHIFTS TO EXTENT OF COOL DOWN 
BY MIDWEEK. 

MODEL QPF LEAVES A LOT TO BE DESIRED WITH ETA/NGM MISSING WI CONVECTION WHILE
DEPICTING DECENT QPF OVER PORTIONS OF CWA AT 06Z...AND NOTHING
SHOWING UP ON RADAR...YET THAT IS. THIS IS WHERE FIRST CHALLENGE RESIDES.
WEAK BOUNDARY WHICH AIDED CONVECTION OVER PORTIONS OF CWA ON SUN STILL EVIDENT
IN PRESSURE AND WIND FIELDS LYING NEAR A LINE FROM CEDAR RAPIDS TO MOLINE.
CEDAR RAPIDS WINDS AT SURFACE CONTINUE TO BACK AND ARE NOW 140/05.
LINE OF CONVECTION SURGING SOUTHEAST THROUGH NORTHWEST IA WITH REPORTS STILL
OF 36-50 KTS FROM SPENCER IA AND FAIRMONT MN. LLVL JET NOT DECENT BUT
NOT AS STRONG FURTHER INTO IA WITH SLATER SHOWING SOUTHWESTERLY AT 25 KTS AT 
H85. CONVECTION HAS WEAKENED AND SLOWED IN FORWARD PROGRESS BUT STILL
MOVING SOUTHEAST AT NEAR 30 KTS. BOUNDARY APPEARS TO BE INTENSIFYING WITH 
FRONTOGENESIS DUE TO INCREASING DYNAMICS...THUS CONCEPTUAL MODELING
SUGGESTS CONVECTION WILL CONTINUE TO PROPAGATE AND/OR DEVELOP ALONG AND NORTH
OF BOUNDARY WHICH WOULD PUT HIGHEST POPS NORTH HALF TODAY. 
WILD CARD IS VORT MAX OVER NORTHERN MO AND INTERACTION WITH BOUNDARY WITH
AVN AND UKMET INDICATING PVA MAX BY EARLY AFTERNOON. STILL WATCHING
SOUTHERN CWA EARLY THIS MORNING. ACTIVITY BEING HELD AT BAY ATTIM AS ENERGY TIED
UP IN CONVECTION TO OUR NORTH/WEST...BUT AS THIS WEAKENS COULD OPEN 
THE DOOR OF OPPORTUNITY FOR DEVELOPMENT ACROSS THE SOUTH WITHIN THETA-E AXIS.
ALL THINGS ASIDE FORCING FAVORABLE FOR CONVECTION ACROSS CWA TODAY. 
ETA AND AVN TO LESSER EXTENT SUGGESTIVE OF TRIPLE POINT IN WESTERN CWA THIS
AFTERNOON WHICH WOULD ENHANCE QPF NORTH HALF. WILL CONTINUE TO MONITOR
LATEST RADAR/SATELLITE TRENDS AND UTILIZE CONCEPTUAL MODELING TO ASSIST WITH
FIRST PERIOD POPS. INTIAL THOUGHTS WILL BE TO HAVE HIGHEST POPS NORTHERN
1/2 TO 2/3RDS. TEMP FORECAST DOESN/T GET MUCH TRICKIER WITH HIGH BUST POTENTIAL.
ANY DECENT SOLAR INSOLATION FOR A FEW HOURS AND TEMPS WILL SOAR TO AT OR
JUST ABOVE SUNDAY/S LEVELS. INTIAL IMPRESSION IS THERE WILL BE A LOT OF DEBRIS
AROUND...BUT WAITING TO SEE CONVECTIVE TRENDS PLAY OUT SOME MORE BEFORE
DECIDING. TOUGH CALL FOR SURE. SEVERE POTENTIAL NEXT CONCERN...ALTHOUGH GIVEN
DYNAMICS NOT REALLY A QUESTION OF WHETHER THERE WILL BE SOME SEVERE
RATHER A QUESTION OF WHEN AND WHERE. BEST GUESS ON TIMING WOULD BE IN THE
23Z-05Z TIMEFRAME. MESOSCALE UNCERTAINTIES REGARDING BOUNDARIES/INSTABILITY
MAKING THINGS A BIT DIFFICULT.  SHEAR FAIRLY UNIDIRECTIONAL
WITH NICHOLS LOCAL CONVECTIVE SEVERE WEATHER ASSESSMENT WORKSHEET SUGGESTING
PRIMARY THREAT DAMAGING WINDS WITH POTENTIAL FOR BOW ECHO/LEWP PATTERN.
SECONDARY THREATS HEAVY RAIN AND HAIL.  MORE HEATING WILL LEAD TO STRONG
DESTABILIZATION AND MUCH GREATER POTENTIAL ON WINDS. IF THIS WERE TO OCCUR THEN
GUSTS OF 70+ KTS NOT OUT OF THE QUESTION. WILL TRY AS BEST AS POSSIBLE TO
CONVEY POSSIBILITIES AND POTENTIAL IN SIG WX OUTLOOK. 
 
MODELS REMAIN CONSISTENT IN HINTING AT SECONDARY WAVE RIDING NORTHEAST ALONG
FRONTAL ZONE ON TUE...GIVING S/E SECTIONS DECENT SHOT OF RAIN.
AVN APPEARS TO SUFFER FROM USUAL BIAS OF BEING TOO FAR NORTH IN COLD AIR WITH
QPF...THUS WILL GO WITH CONCEPTUAL MODELING PLACING MOLINE TO WASHINGTON
ON NORTHERN FRINGES OF QPF. GOING MAINLY WITH RAIN WITH SEVERE STRATIFICATION
IN COLD AIR...ALTHOUGH COULD BE SOME THUNDER IN FAR S/E. GOING LIKELY POPS
IN S/E LOOK GOOD. TEMPS AGAIN VERY CHALLENGING ON TUE WITH CLOUDS AND RAIN.
MET GUIDANCE APPEARS TOO WARM AND WILL SIDE TOWARD COOLER MAV/FWC THOUGH
SHAVING A FEW DEGS. LIKELY TO BE BARELY SITTING IN 70S MOST AREAS WITH FEW U60S
POSSIBLE. A BIG CHANGE FOR SURE!

LOOKING LONGER TERM...LONGWAVE PATTERN SUGGESTIVE OF MAINTAINING TROUGHING
THROUGH CENTRAL US RESULTING IN ACTIVE WX. THUS...WOULD NOT BE 
SUPRISED TO SEE SOME BIG CHANGES IN MODELS NEXT FEW DAYS...AS AVN/S DEPICTION
OF ZONAL FLOW FROM COAST TO COAST...UNREALISTIC! 

BACK TO NEAR TERM HIGHLIGHTS...CERTAIN TO SEE HEAVY RAIN EVENT NEXT 24 TO
36 HOURS WITH WIDESPREAD RAINFALL AMOUNTS OF 1+ INCHES BY 12Z WED
WITH AREAS OF 2 TO 4 INCHES QUITE REASONABLE BASED ON STRENGTH OF FORCING AND
MOISTURE...THUS WILL CONTINUE WITH ESF HIGHLIGHTING HEAVY RAIN AND
POSSIBLE LOW END FLOODING. WILL ALSO CONTINUE WITH HEAVY RAIN WORDING IN ZONES.

ZONES LIKELY TO BE DELAYED SOME AS WAITING TO SEE CONVECTIVE TRENDS PLAY OUT.


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


M^2