[LeArc] Forecast Discussion : MLI@ 4/19/2003 3:52:21 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 190850
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
349 AM CDT SAT APR 19 2003

DISORGANIZED LINE OF SHOWERS AND THUNDERSTORMS THAT HAVE BEEN MOVING 
ACROSS EASTERN IA OVERNIGHT ARE NOW TRANSITIONING INTO FEW STRONG 
CELLS WITH PEA HAIL. THIS ACTIVITY OCCURRING UNDER VORT LOBE 
ROTATING AROUND H5 LOW OVER NORTHEAST ND AND H85 THETA E RIDGE AXIS 
PUSHING THROUGH EASTERN IA INTO NW IL EARLY THIS MORNING. MSAS 
SHOWED SURFACE LOW EAST OF KFSD WITH WEAK WARM FRONT SOUTHEAST INTO 
NW IL. STRONGER WARM FRONT WAS STILL TO SOUTHWEST ACROSS NORTHERN MO 
TO SOUTHERN IL WITH PUSH OF MID 50S DEWPOINTS TO SOUTH.  SECONDARY 
DEEPER LOW WAS OVER TX/OK PANHANDLE REGION. MAIN FORECAST CHALLENGE 
IS RAIN AND THUNDERSTORM POTENTIAL NEXT 36 HOURS AS SECONDARY UPPER 
LOW OVER SW CONUS PUSHES NORTHEAST TO REINFORCE LOW OVER UPPER 
MISSOURI RIVER VALLEY SATURDAY NIGHT. 

IN SHORT TERM...SOME SEVERE POTENTIAL EXISTS IN FIRST PERIOD. MOST 
CONVECTION SHOULD BE OUT OF CWA BY SUNRISE. QUESTION WILL THEN BE 
HOW MUCH CLEARING OCCURS THIS MORNING TO ALLOW INSOLATION AND 
DESTABILIZATION BEFORE UPSTREAM SYSTEM MOVES IN EARLY AFTERNOON. 
SATELLITE WATER VAPOR AND FOG IMAGERY HAS SHOWN LARGE CLEARING AREA 
OVER SW IA INTO KS/NEB EARLIER THAT SHOULD REACH INTO SE IA THIS 
MORNING. RECENT TRENDS SHOW LARGE CLOUD SHIELD FROM MCS OVER OK/S 
CENTRAL KS STREAMING NE AND THIS MAY LIMIT AMOUNT OF WARMING. THUS 
WILL NOT BUY 00Z META WITH 20 DEG RISE THIS MORNING INTO MID 70S. IF 
ENOUGH SUNSHINE BREAKS THROUGH FOR TEMPS TO REACH NEAR 75...ETA 
FORECAST PLACES SB CAPES IN RANGE OF 700 TO 800 J/KG WITH LI/S FROM 
-2 TO -4...AND H5 TO H7 LAPSE RATES FROM 7 TO 7.5 DEG C/KM. STRONG 
JET LEVEL DIVERGENCE ARRIVES ESPECIALLY OVER EASTERN IA THIS 
AFTERNOON WITH STRONG H5 VORT MAX AND DECENT H7 OMEGA VALUES. 
NEGATIVE FACTOR FOR ORGANIZED SEVERE WEATHER WILL BE WIND PROFILES 
BECOME MORE UNIDIRECTIONAL BY AFTERNOON WITH UNIMPRESSIVE SURFACE TO 
3 KM HELICITY BY MIDDAY. STILL THINK STRONG ENOUGH DYNAMICS AND 
UPPER DIVERGENCE WILL COMPENSATE FOR SOMEWHAT LIMITED INSTABILITY 
AND LOW LEVEL SHEAR AND WILL KEEP MENTION OF ISOLATED SEVERE IN 
ZONES FOR AFTERNOON. 

FOLLOWING COMPROMISE OF ETA/GFS MODELS THAT ARE MORE CLOSELY IN 
AGREEMENT THAN PREVIOUS RUNS...STRONGER MID LEVEL VORTEX PUSHES 
THROUGH AROUND MIDNIGHT WITH WIDESPREAD CONVECTION CONTINUING 
OVERNIGHT ACROSS ENTIRE CWFA. WITH PRECIP H20 IN 1.3 TO 1.4 
RANGE...SURFACE DEWPOINTS 55 TO 60...AND H85 DEWPOINTS FROM 8 TO 
10...RAIN COULD BE HEAVY AT TIMES BUT NOT ENOUGH TO WARRANT ANY 
HYDRO HIGHLIGHTS AS DO NOT EXPECT QPF TO APPROACH MOSTLY HIGH 
GUIDANCE FF VALUES ACROSS AREA. WILL BE BREEZY/WINDY TONIGHT 
FOLLOWING MORE WESTWARD PLACEMENT AND TRACK OF UPPER LEVEL AND 
SURFACE LOW...SIMILAR TO UKMET.  

SUNDAY TO BE MAINLY CLOUDY...COOL AND SHOWERY WITH OCCLUDED LOW TO 
NORTH. HAVE LIMITED THUNDER MENTION TO MORNING. FEW CHANGES MADE TO 
GRIDS BEYOND WEEKEND DUE TO SHORT TERM FOCUS. UPPER LOW FILLS AND 
MOVES NORTHEAST WITH OMEGA TYPE BLOCKING SETTING UP BY MIDWEEK.
NEXT PRECIP CHANCES KEPT OVER MAINLY SOUTH LATE WEEK AS NEXT WESTERN 
UPPER LOW MOVES OUT OF CENTRAL ROCKIES. 

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

$$

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