[LeArc] Forecast Discussion : MLI@ 3/18/03 3:08:47 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 182116
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
316 PM CST TUE MAR 18 2003
 
ACTIVE WEATHER NEXT SEVERAL DAYS AS LARGE SLOW MOVING VORTEX OVER 
CO/NM PUSHES WAVES OF INSTABILITY AND OVERRUNNING RAIN INTO FORECAST 
AREA THROUGH LATE WEEK. ANTICIPATED TIGHT NORTH TO SOUTH THERMAL 
GRADIENT ACROSS CWFA THIS AFTERNOON...WITH UPPER 40S NORTH TO UPPER 
60S SOUTH. THIS WAS WITH HELP OF STRONG NORTHEAST LOW LEVEL 
FLOW OF COLDER AIR FROM GREAT LAKES THAT HAD DRIVEN SURFACE FRONT TO 
A POSITION FROM CENTRAL IL WEST ACROSS NORTHERN MO OVERNIGHT AND ALSO
REINFORCED BY INSOLATION FROM BY LARGE HOLE IN CLOUD COVER 
OVER N CENTRAL IL. LATEST 88D MOSAICS SHOW CONVECTION FIRING ALONG 
FRONT IN CENTRAL IL ALONG AND SOUTH OF FRONT IN MO WHERE ATMOSPHERE 
HAS DESTABILIZED. FORECAST CHALLENGE IS POPS AND THUNDERSTORM 
POTENTIAL THROUGH REST OF WEEK. 

ALL MODELS FAIRLY CONSISTENT WITH UPPER FEATURES THROUGH THURSDAY... 
WITH BIGGEST DIFFERENCES AT SURFACE. ALL HAVE DIFFERENCES IN SURFACE 
LOWS MOVING IN DUMBELL FASHION UNDER UPPER LOW IN SOUTHERN PLAINS. 
ETA IS ALONE IN KEEPING MAIN LOW BACK OVER SOUTHERN IL BY 12Z 
FRIDAY...AND WILL LEAN TOWARD MORE CONSENSUS SOLUTION OF AVN AND UK 
WITH LOW OVER LOWER MI BY THIS TIME. 

IN SHORT TERM...MODELS HAVE HAD POOR HANDLE ON FORCING AND QPF 
PLACEMENT OVER FORECAST AREA PAST COUPLE DAYS...AND SEE NO IMMEDIATE 
IMPROVEMENT WITH EVEN SHORT RANGE MODELS NOT HANDLING CONVECTION 
AREA TO SOUTH WELL. AS RESULT...HAVE CUT BACK POPS TONIGHT TO MAINLY 
AFTER MIDNIGHT EXCEPT IN SOUTH WHERE SOME DECAYING SHOWERS AND 
POSSIBLY TSRA WILL STREAM NW PAST FRONT BEFORE DECAYING. BETTER 
FORCING ARRIVES TOWARD MORNING AS VORT PUSHING INTO AR STREAMS NORTH 
INTO AREA. OVERRUNNING RAIN SHOULD BE WIDESPREAD WED AND KEPT 
CATEGORICAL POPS AS MAIN LOBE OF VORTICITY PUSHES TOWARD AREA WITH 
DEEP MOIST SOUTHERLY FLOW DEVELOPING. THIS COULD PUSH STEEP H5-H7 
LAPSE RATES AND LI/S AS LOW AS -4 ACCORDING TO GFS INTO AREA LATE 
WED NIGHT INTO FRIDAY. THUS...TSRA ADDED OR KEPT IN SOUTH AND 
SOUTHEAST WED NIGHT INTO THURSDAY. TOO MUCH MODEL UNCERTAINTY IN 
DETAILS TO ASSESS SEVERE POTENTIAL...BUT THURSDAY STILL HAS 
POSSIBILITY FOR ELEVATED STORMS WITH SEVERE HAIL IN SOUTHEAST HALF. 

TEMPERATUREWISE...STRONG EAST FLOW WILL CONTINUE TO REINFORCE 
THERMAL GRADIENT AND WENT BELOW GUIDANCE IN NORTH AND NEAR TO ABOVE 
IN SOUTH TONIGHT THROUGH WEDNESDAY. WENT NEAR MAV/FWC NORTH TONIGHT 
AND WEDNESDAY AS MET TOO WARM...ESPECIALLY IN THE SOUTH WEDNESDAY
AND THURSDAY GIVEN EXPECTED RAIN.

MODEL DISAGREEMENTS CONTINUE WITH HANDLING OF WEAKENING MAIN UPPER 
LOW MOVING INTO GREAT LAKES AND SECONDARY NORTHERN STREAM WAVE 
MOVING OUT OF DAKOTAS. FRIDAY STILL LOOKS UNSETTLED WITH POTENTIAL 
FOR SHOWERS AND KEPT BELOW NORMAL TEMPERATURES. 

FRIDAY THROUGH TUESDAY...SOME DIFFERENCES WITH NORTHERN STREAM 
SHORTWAVE TO PASS TO NORTH INTO GREAT LAKES FRIDAY INTO SATURDAY. 
12Z GFS FASTER AND DEEPER WITH UPPER LOW TO PASS INTO LOWER MI 
FRIDAY NIGHT...TRENDING TOWARD 00Z UK RUN WHICH LOOKS ACCEPTABLE. 
THUS WILL KEEP SHOWERS GOING INTO LATE FRIDAY NIGHT. SURFACE RIDGE 
BUILDS IN FROM WEST SATURDAY FOR COOL AND DRY WEATHER...THEN RETURN 
FLOW DEVELOPS SUNDAY FOR WARMING TREND. NORTHERN STREAM SHORTWAVE 
COMBINES WITH SOUTHERN STREAM SYSTEM MOVING INTO SW CONUS TO PUSH 
FRONT THROUGH MONDAY NIGHT WITH OVERRUNNING TYPE SITUATION TOWARD 
MIDWEEK INDICATED BY GFS FOR NEXT PRECIP CHANCES. WILL NOT GO ALONG 
WITH GFS AND INTRODUCE TUESDAY AS DRY...SINCE IT HAS A BIAS OF 
BRINGING SYSTEMS IN TOO QUICK. TEMPERATURES WILL BE NEAR OR BELOW 
NORMAL THROUGH WEEKEND AND STAYED NEAR TO BELOW GUIDANCE OVER 
WEEKEND...AND THEN ABOVE ON MONDAY FOR TYPICAL PREFRONTAL WARMING 
NOT HANDLED WELL BY MODELS. TUESDAY WILL BE MUCH COOLER AS FRONT 
STALLS TO SOUTH WITH COOL EASTERLY FLOW AND WENT WITH A TIGHTER 
NORTH TO SOUTH THERMAL GRADIENT THAN DEPICTED BY GUIDANCE.  

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

$$

DLS