[LeArc] Forecast Discussion : MLI@ 5/30/2002 2:17:16 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 301912
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
210 PM CDT THU MAY 30 2002

.OVERVIEW...ANALYSIS SHOWS FAST JET STREAK ACROSS MONTANA TURNING
SOUTHEAST.  LEADING EDGE OF ENERGY PRODUCING A BROAD WIND SHIFT LINE OR
WEAK FRONT NOW INTO FAR NW IOWA.  MAIN DIFFERENCE ARE LOWER DEWPOINTS
BEHIND BOUNDARY.  ANALYSIS SUPPORTS SYSTEM TO PUSH SE ACROSS AREA THIS
EVENING AND INTO EARLY FRIDAY BEFORE BECOMING STATIONERY.  SATELLITE
SUGGESTING MOST MID LEVEL MOISTURE BEING SHUNTED EAST IN ADVANCE OF
SYSTEM WHICH MAY SUPPORT MORE ENERGETIC CONVECTION TONIGHT.

...ASSESSING POPS AND SEVERE POTENTIAL THIS EVENING WITH FRONT AND
THEN VERY UNSETTLED PATTERN THIS WEEKEND INTO NEXT WEEK WITH HEAVY RAIN
AND SEVERE WEATHER POTENTIAL...

.DIAGNOSIS AND DAYS 1-3...LATEST 18Z SURFACE DATA SUPPORTS MARGINAL
FORCING FOR LIMITED CONVECTION WITH ETA CLOSEST AT 18Z ON MOST LOW
LEVEL FEATURES AND CURRENT CONVECTIVE COVERAGE ALONG BOUNDARY...WITH
JUST SOME CELLS IN EASTERN WISCONSIN...AND ENHANCED CUMULUS NEAR MASON
CITY.  CALCULATIONS FROM DVN SVR WX CHKLST AND BLEP TECHNIQUE SUPPORT
ISOLATED TO SCATTERED STORMS LATE PM INTO EVENING HOURS WITH FAVORABLE
CONDITIONS FOR ROTATING CELLS OR SUPERCELLS...MOVING SSE.  HOWEVER...
QUESTION ON BL INSTABILITY AND TRIGGER...SO TORNADOES CHANCES AT PRESENT
APPEAR REDUCED...WILL NEED FOLKS TO MONITOR THIS FOR CHANGES NEXT 3-6
HOURS FOR ANY CHANGES OR LOCAL BOUNDARY DEVELOPMENT.  SO...ANTICIPATE
PRIMARY THREAT FOR MAINLY SOME LIMITED HAIL WITH RELATIVELY HIGH WBZ
~10.5K AND SOME STRAIGHT LINE OR ENHANCED ROTATIONAL DOWN-DRAFTS IN
ROTATING CELLS...BEST CHANCE NORTH OF HIGHWAY 34.   AVN AND ETA MODELS
DIFFER ON AMOUNT OF MOISTURE AT TOP BL WHICH GREATLY IMPACTS MAX DOWN-
DRAFTS POTENTIAL. WILL LEAN TOWARD ETA WHICH IS MORE MOIST BASED CURRENT
SKY CONDITIONS. THUS...THIS WOULD PRODUCE NOT AS HIGH WINDS AS AVN PER
BLEP TECHNIQUE. COMPUTING WINDS FOR SFC T/TD OF ~88/68..BLEP YIELDS NEAR
50KTS STRAIGHT LINE OR UP TO 84KTS IN MESO ENHANCED DOWNDRAFT TIL SUNSET
AND THEN DROPPING NEAR TO SLIGHTLY AFTER SUNSET ~36 KTS STRAIGHT LINE UP
TO 64 KTS IN ROTATION FOR T/TD ~82-83/66.  AVN PRODUCES VALUES 15-
20 KTS HIGHER.  ANYWAY...EXPECT CELLS AND FRONT TO MOVE EAST OR DIE
AFTER MIDNIGHT WITH DRIER AIR MOVING IN SUPPORTING LESS HUMID
CONDITIONS. WILL GO ON HIGH SIDE OF GUIDANCE BLEND INTO SATURDAY WITH
POPS LATE FRIDAY NIGHT MOST AREAS INTO SATURDAY WITH LIKELY WORDING
SOUTHERN AREAS AND CHANCE POPS NORTH.  THEN PATTERN REMAIN CONDUCIVE FOR
SIGNIFICANT STORMS WITH E-W BOUNDARY NEARBY AND IMPULSES EMBEDDED IN
ZONAL JET. THUS...EXPECT TWO TO THREE EPISODES OR MORE OF MCS/MCC
CONVECTION...OR EVEN INTENSE BOW ECHO/DERECHO VARIETY DUE TO SIGNIFICANT
BOUNDARY AND LOTS OF INSTABILITY AND MOISTURE GRADIENT TO FEED ON.  WILL
HAVE TO KEEP CHANCE POPS FOR NOW INTO SUNDAY NIGHT AS NO COHERENT AND
CONSISTENT PATTERN STANDS OUT FOR TIMING OF EPISODES OF CONVECTION.
WILL DO ESF TO EMPHASIZE HEAVY RAIN POTENTIAL.

.EXTENDED (MON-WED)...MEDIUM MODELS VARY QUITE A BIT SO WILL CONTINUE
CHANCE POPS INTO TUESDAY WITH SOME COOLER AND DRIER AIR SUGGESTED
WEDNESDAY.  AGAIN PATTERN FAVORABLE FOR HEAVY RAINS WITH ABOVE NORMAL
SEVERE RISKS.  CLOUD COVER DEFINITELY TO GREAT IMPACTS ON TEMPS AND
POSSIBLE LAKE EFFECT MONDAY...WILL TRY AND INCORPORATE TRENDS INTO
MEX/FMR GUIDANCE.

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

NICHOLS