[LeArc] Forecast Discussion : MLI@ 5/7/2003 3:57:53 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 070855
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
400 AM CDT WED MAY 7 2003

SHRA/TSRA OVER FAR NORTHERN COUNTIES OF CWA EARLY THIS MORNING AND 
LIFTING N PER REGIONAL COMPOSITE.  PCPN OCCURRING IN VICINITY OF 
INVERTED TROF EXTENDING NORTH FROM SURFACE LOW OVER KSTL AT 07Z
AND AHEAD OF MID LEVEL TROF MOVING THROUGH WRN IA.  H5 ANALYSIS TUE
EVENING SHOWED. REGION UNDER INFLUENCE OF BROAD SW FLOW WITH SEVERAL 
IMPULSES LINED UP TO THE WEST.  

MODELS CONTINUE TO SUGGEST AN ACTIVE PERIOD THROUGH THE WEEKEND AS
A SUCCESSION OF S/W MOVE THROUGH THE WESTERN U.S. TROF AND EJECT OUT 
IN TO THE PLAINS.  MODEL SOLUTIONS ARE SIMILAR...BUT THE THERE ARE 
TIMING DIFFERENCES WITH THE GFS GENERALLY SLOWER THAN THE ETA.  A 
DIGGING WESTERN U.S. TROUGH SUPPORTS THE SLOWER GFS.  

MAIN FORECAST ISSUE TODAY WILL BE WALKING THE PCPN CURRENTLY OVER 
NORTHERN CWA OUT OF THE REGION THIS MORNING...THEN LINGER CLOUD 
COVER AND IT IMPACTS ON TEMPS TODAY.  INVERTED TROUGH AND MID LEVEL 
TROUGH WILL STILL BE OVER CWA AT 12Z THIS MORNING...PROVIDING AN 
OPPURTUNITY FOR ADDITIONAL SHRA DEVELOPMENT.  WILL KEEP SCT WORDING 
IN NORTHERN HALF OF CWA FOR THE EARLY MORNING HOURS. CLOUDS WILL 
LINGER IN THE EAST THROUGH THE DAY BUT...COMBINATION OF DIMINISHING 
LOW LEVEL MOISTURE AND SUBSIDENCE BEHIND DEPARTING SURFACE LOW WILL 
HELP THE CLOUD COVER BREAK UP THIS AFTERNOON IN THE WEST.  BASED ON THIS
THINKING TEMPS IN GOING FORECAST LOOK REASONABLE AND ARE IN 
AGREEMENT WITH MOS NUMBERS.

MODELS HAVE MADE MAJOR SHIFT IN HOW THEY HANDLE SHORT WAVE ENERGY 
MOVING OF WESTERN U.S. ON THURSDAY.  THEY ARE NOW SUGGESTING SURFACE 
LOW WILL ROTATE NORTH ACROSS WESTERN IA INSTEAD OF MOVING THROUGH SE IA
PER YESTERDAYS RUNS.  WARM FRONT APPROACHING CWA THURSDAY WILL 
SPREAD AROUND OF SHRA/TSRA NORTH ACROSS CWA THURSDAY.  GFS 
SUGGESTING THAT PCPN WILL HOLD OFF UNTIL LATE IN THE DAY...WITH ETA 
A 8 HOURS SOONER.  I PREFER THE SLOWER SOLUTION...BUT WITH SPC 
BRINGING SLIGHT RISK AS FAR NORTH AS SOUTHERN CWA BY THURSDAY 
MORNNING...WILL GO AHEAD AND INTRODUCE POPS FOR LATE TONIGHT AND 
THURSDAY MORNING.  LOOKS LIKE HEAVY RAIN THREAT IS STILL PRESENT WITH
H8 DEWPOINTS WELL INTO THE TEENS AND SURFACE DEWPOINTS AT LEAST IN 
THE MID 60S SOUTH OF THE WARM FRONT PROVIDING A GOOD MOISTURE SOURCE 
FOR TSRA ON THE COLD SIDE OF THE FRONT.  HOWEVER...WITH WARM FRONT 
LIFTING STEADILY NORTH FEEL HEAVY RN THREAT WILL NOT LAST LONG 
ENOUGH TO CAUSE SIGNIFICANT HYDRO PROBLEMS. THUS NO HYDRO HEADLINES 
AT THIS TIME.  SEVERE THREAT WILL ALSO BE THERE WITH LARGE HAIL THE 
MAIN THEAT THURSDAY NIGHT/EARLY FRIDAY MORNING NORTH OF THE WARM 
FRONT.  COLD FRONT/OCCLUSION SWEEPS THROUGH CWA EARLY FRIDAY.  
TIMING IS NOT CONDUSIVE FOR A BIG SEVERE EVENT...BUT WITH STRONG 
UPPER DYNAMICS...IT CAN'T BE RULED OUT.  FRONT HANGS UP ACROSS 
NORTHERN MO/CENTRAL IL FRIDAY.  A MUCH STRONGER SYSTEM MOVES OUT OF 
WESTERN U.S. FRIDAY NIGHT AND SATURDAY AND SPINS UP ANOTHER WAVE 
ALONG THE BOUNDARY.  THIS WAVE IS PROGGED TO MOVE NORTHEAST THROUGH 
WESTERN IOWA SATURDAY NIGHT.  THIS SYSTEM WILL AGAIN HAVE THE 
POTENTIAL TO PRODUCE LOCALLY HEAVY RAIN/SEVERE HAIL AHEAD OF THE 
WARM FRONT FRIDAY NIGHT AND SEVERE STORMS AHEAD OF THE COLD FRONT 
SATURDAY EVENING.  TIMING WITH THIS SYSTEM IS A LITTLE FASTER THAN 
PREVIOUS FORECAST SUGGESTED AND WILL ADJUST TIMING OF STRONGER 
STORMS INTO SATURDAY AFTERNOON/EVENING.  

GFS STILL SHOWING A GOOD COOL DOWN SUNDAY WITH H8 TEMPS AROUND 0C
MOVING INTO REGION.


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

$$
DLF