[LeArc] Forecast Discussion : MLI@ 11/17/02 3:17:10 PM

[learc@mailman.qth.net]

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


FXUS63 KDVN 172129
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
328 PM CST SUN NOV 17 2002

WEAK N-S SURFACE RIDGE OVER CWFA AT MIDDAY WITH COLD AIR IN PLACE 
AND SUBSIDENCE LIMITING TEMPERATURES TO 30S DESPITE SUNNY SKIES. 
UPPER LEVEL TROUGH THAT DOMINATED PAST FEW DAYS NOW WELL TO EAST 
WITH SHORTWAVE RIDGING TO OUR NW. OUT WEST...AN IMPRESSIVE UPPER 
TROUGH SEEN ON WATER VAPOR MOVING INTO ID AND NV WILL SPELL RAPID 
CHANGE TO OUR WEATHER TO START WORKWEEK. FORECAST CHALLENGE IS 
PRECIPITATION TYPE AND PROBABILITY MONDAY AS DEVELOPING LEE SURFACE 
LOW MOVES RAPIDLY THROUGH MID MISSISSIPPI VALLEY. 

SURFACE OBSERVATIONS AND PRESSURE ANALYSIS INDICATED LOW BEGINNING 
TO SPIN UP OVER SE CO WITH WARM FRONT ARCHING TO ITS EAST INTO SW 
MO. FORECAST MODELS SIMILAR IN SHORT RANGE WITH THIS 
SHORTWAVE...THEN GFS A BIT SLOWER WITH TROUGH MOVING THROUGH CENTRAL 
PLAINS ON MONDAY. AT SURFACE...GFS AND NGM HAVE SURFACE LOW TRACKING 
INTO CENTRAL MO BY 18Z...WHICH LOOKS MORE REASONABLE GIVEN LOCATION 
OF CURRENT SURFACE THERMODYNAMIC FIELDS AND THUS MAINLY FOLLOWED 
AVN/GFS.

CI STREAMING INTO CENTRAL IA WILL BE INTO MUCH OF FORECAST AREA BY 
EARLY EVENING AND RETARD RAPID COOL DOWN AFTER SUNSET WITH LOW 
SURFACE DEWPOINTS IN PLACE. H85 WARM AIR ADVECTION AHEAD OF TROUGH 
AND ISENTROPIC LIFT DEVELOPING TOWARD MORNING WILL INCREASE CLOUD 
COVER TO OVERCAST BY MORNING. THIS CLOUD COVER SHOULD PREVENT MUCH 
DROP OFF AFTER MIDNIGHT WITH TEMPERATURES HOLDING STEADY. WENT NEAR 
OR BELOW COLDER MAV GUIDANCE WITH LOWER 20S NORTH AND UPPER 20S 
SOUTH. QG FORCING DEVELOPS AT MID LEVELS AFTER 06Z WHICH SHOULD 
BEGIN PRECIPITATION PROCESS TO GRADUALLY MOISTEN BOUNDARY LAYER FROM 
TOP TO BOTTOM. INITIALLY DRY AIRMASS AT SURFACE SHOULD KEEP MOST 
PRECIP FROM REACHING GROUND UNTIL DAYLIGHT HOURS MONDAY MORNING AND 
ADJUSTED WORDING. CRITICAL THICKNESS VALUES AND MODEL SOUNDINGS 
POINT TOWARD POSSIBLE BRIEF ZR IN MORNING...BEFORE WEAK SURFACE WARM 
AIR ADVECTION RAISES SURFACE TEMPERATURES TO ABOVE FREEZING...THEN A 
DEEP ENOUGH ABOVE FREEZING LAYER FOR RAIN EVENT AS STRONG QG FORCING 
AND JET LEVEL COUPLING AND DIVERGENCE PROVIDE LIFT THROUGH DAY. HAVE 
RAISED POPS TO LIKELY CATEGORY FOR NORTHERN 2/3RDS WITH HIGH 
SCATTERED IN SOUTH. SURFACE TROUGH OUT OF EASTERN ZONES EARLY 
EVENING AND WILL KEEP SOME SCATTERED POPS FOR RAIN OR SNOW SHOWERS 
GOING THERE. CLOUDS AND RAIN SHOULD LIMIT MUCH RISE IN TEMPERATURES 
AND WENT CLOSER TO COOLER MAV. NW SURFACE FLOW PREVAILS FOR TUESDAY 
AND SAW NO REASON FOR HUGE WARMUP FORECAST BY ETA AND STAYED CLOSER 
TO MAV.

IN LONG RANGE...NO SIGNIFICANT CHANGES TO EXTENDED. NEXT SYSTEM 
PASSES MAINLY TO NE ON THURSDAY WITH UPPER NW FLOW FROM REBOUNDING 
WESTERN CONUS RIDGE. STUCK WITH GFS/MRF IDEA OF SHORTWAVE ON
SATURDAY TO SUPPORT NEXT SIGNIFICANT RAIN CHANCES.

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

DLS