[LeArc] Forecast Discussion : MLI@ 9/27/02 2:13:59 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 271922
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
222 PM CDT FRI SEP 27 2002

SURFACE HIGH CENTERED OVER MN AND LOW PRESSURE REMNANT OF ISIDORE 
OVER SE OHIO RESULTING IN 4-5KFT DEEP COOL MOIST NORTH TO NORTHEAST 
FLOW HOLDING TEMPERATURES ONLY IN MID 50S TO LOWER 60S OVER FORECAST 
AREA AT 18Z. VISIBLE SATELLITE IMAGERY SHOWS SOME LARGE HOLES 
DEVELOPING IN CENTRAL IA. LARGE BREAKS IN ST ALSO BEING REVEALED IN 
SOUTHEAST IOWA INTO NORTHWEST ILLINOIS AS MID LEVEL DECK DISSIPATES 
AND MOVES EAST. INITIAL FORECAST CHALLENGE IS DEGREE OF CLEARING 
EXPECTED IN LOW CLOUD DECK AND IMPACTS ON TEMPERATURE AND FOG 
POTENTIAL. IN LONGER TERM...TEMPERATURES MAIN CONCERN.

12Z ANALYSIS SHOWED TWO SIGNIFICANT SHORTWAVES H5 OVER CONUS...ONE 
OVER ID AND THE OTHER INDIANA. IN BETWEEN...A WEAKER WAVE THAT 
PROCUCED LIGHT SHOWERS THIS MORNING WAS MOVING INTO NW IL AT MIDDAY. 
12Z MODELS CONSISTENT WITH DIGGING WESTERN CONUS LOW AND ZONAL TO SW 
UPPER FLOW OVER FORECAST AREA THIS WEEKEND. THIS LOW RAPIDLY LIFTS 
NE MONDAY WITH ACTIVE SW FLOW WITH WEAK IMBEDDED SHORTWAVES DEPICTED 
THROUGH LATE WEEK OVER CWA. 

MODEL RH FIELDS SUGGEST CLEARING OVER MOST OF FORECAST AREA THIS 
EVENING. HOWEVER...WITH FAIRLY DEEP LOW LEVEL FLOW GOING GRADUALLY 
FROM NE TO SE OVERNIGHT AS HIGH MOVES EAST...LOW LEVEL RH FIELDS 
SHOULD REMAIN RATHER HIGH AND WILL HAVE TO MONITOR CLOUD TRENDS 
UNTIL LAST MINUTE. EVEN IF ST CLEARS OUT EARLY...THE LOW LEVEL FLOW 
COULD BRING IT BACK IN ESPECIALLY IN THE EAST TOWARD MORNING. THINK 
FOG POTENTIAL STILL EXISTS TOWARD MORNING FOR AREAS WITH SIGNIFICANT 
CLEARING TO ALLOW RADIATIONAL COOLING. WILL KEEP MENTION OF PATCHY 
FOG IN ZONES...BUT DO NOT EXPECT ANYTHING DENSE SINCE SURFACE WINDS 
SHOULD BEGIN TO PICK UP TOWARD MORNING. WILL STAY ON COOL SIDE OF 
GUIDANCE WITH LOWS.

12Z MOS GUIDANCE COMING IN SIGNIFICANTLY WARMER THAN 00Z RUN FOR 
HIGHS SATURDAY...WITH ETA AS MUCH AS 6 TO 9 DEG F WARMER. DEVELOPING 
LOW IN HIGH PLAINS RESULTS IN STRONG WARM AIR ADVECTION WITH H85 
TEMPERATURES BY LATE AFTERNOON SUPPORTING HIGHS FROM MID 70S N TO 
AROUND 80 SOUTH AND WILL RAISE BY A CATEGORY. ELEVATED SHOWERS AND 
THUNDERSTORMS POSSIBLE SATURDAY NIGHT AS LOW MOVES ACROSS KS WITH 
STRONG MOISTURE RETURN AT H85 WITH DEWPOINTS ABOVE 10 C AT H85 
STREAMING OVER CWA. WILL KEEP SCATTERED POPS GOING FOR SATURDAY 
NIGHT INTO SUNDAY. CLOUDS AND COUPLED SOUTHERLY FLOW WILL HOLD LOWS 
IN MILD MID 50S TO LOWER 60S. SIGNIFICANT MODEL DIFFERENCES IN 
HANDLING OF NORTHERN PLAINS SURFACE LOWS APPEAR SUNDAY AND BEYOND. 
GOING WITH ETA/AVN COMPROMISE...LOOKS LIKE ALL BUT FAR NORTH PART OF 
CWA SHOULD BE IN WARM SECTOR OF WEAKENING LOW OVER EASTERN 
NEB/WESTERN IA SUNDAY. WILL KEEP WITH GOING FORECAST THAT IS 
CONSISTENT WITH NEW GUIDANCE WITH MID 70S NORTH TO MID 80S SOUTH.

IN EXTENDED...COLD FRONT TO MOVE THROUGH LATE TUESDAY AND BRING NEXT 
SIGNIFICANT SHOT OF RAIN. TEMPERATURES TO COOL BACK TO NEAR OR BELOW 
CLIMO FOR HIGHS MID TO LATE WEEK. MRF AND UK SHOW NEXT STRONG 
SHORTWAVE EJECTING FROM SW FOR RAIN CHANCES TO LATE THURSDAY INTO 
FRIDAY TIMEFRAME. 
 
.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

DLS