[LeArc] Forecast Discussion : MLI@ 3/3/03 4:49:22 AM

[learc@mailman.qth.net]

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


FXUS63 KDVN 031059
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
430 AM CST SUN MAR 2 2003

RUNNING BIT BEHIND. FORECAST THAT OF A METEOROLOGICAL MINEFIELD WITH 
BIG BUST POTENTIAL. OF MOST CONCERN IS SYSTEM TUE-TUE NIGHT AND
WHETHER HEADLINES NEEDED. 

SURFACE RIDGE AXIS HAS SHIFTED EAST WITH RETURN FLOW DEVELOPING.
WARM ADVECTION AIDING DEVELOPMENT OF SNOW INTO MN AND NORTHERN PORTIONS
OF IA ATTIM. MODELS IN DECENT AGREEMENT AND DEPICT INCREASING
WARM ADVECTION WITH MODERATE-STRONG ISENTROPIC LIFT AND FRONTOGENETICAL
FORCING DEVELOPING LATE MORNING AND THROUGH THE AFTERNOON. QPF DIFFERS SOME
BUT GENERALLY .10 TO .20 INCH ALONG AND NORTH OF HIGHWAY 30 DWINDLING
TO A COUPLE OF HUNDREDTHS NEAR HIGHWAY 34. ISENTROPIC INSPECTION OF 285K
SURFACE REVEALS 2-3 G/KG MOISTURE. CRITICAL TO AMOUNTS WILL BE 
HOW LONG SATURATION PROCESS TAKES. WITH HIGHER SNOW TO LIQUID RATIOS 
OF 12:1 OR SO POSSIBLE WILL GO WITH 1-2 INCHES NORTHERN 1/3RD...WITH POTENTIAL
FOR 3 INCH SOMEWHERE. AN INCH OR LESS FURTHER SOUTH THROUGH I-80.
HAVE REMOVED PCPN IN FAR SOUTH...EXTREME NORTHEAST MO AND PORTIONS OF WEST
CENTRAL IL AS IT LOOKS LIKE FORCING SHIFTS N/E BEFORE SATURATION OCCURS.
TEMPS TRICKY...WITH CLOUDS AND SNOW. NGM SFC PARCEL TRAJECTORIES SUGGEST
SOURCE REGION NORTHEAST OK WHERE READINGS YESTERDAY WERE IN U30S TO
L40S. WILL TEMPER A BIT ESPECIALLY CENTRAL AND NORTH WHERE PCPN CHCS GREATEST.
ANY LINGERING SNOW OR FLURRIES IS EXPECTED TO SHUTDOWN EARLY THIS EVE 
AS FORCING DEPARTS. 

THEN...CONCERN SHIFTS TO NEXT SYSTEM FOR TUE-TUE NIGHT. MODELS HAVING
TROUBLE RESOLVING PHASING OF NORTHERN STREAM ENERGY IN 
SOUTHERN CANADA AND SHORTWAVE TROUGH IN SOUTHWESTERN STATES. THIS IN TURN
IMPACTS PLACEMENT AND STRENGTH OF SURFACE WAVE ALONG FRONTAL ZONE WHICH
IN TURN AFFECTS PLACEMENT OF MAIN SNOW BAND. NGM AND ETA TRENDING SOUTH
LIKE MOST SYSTEMS THIS WINTER SEASON. MEANWHILE...AVN/GFS AND UKMET ARE 
FURTHER NORTH WITH UPPER JET AND DEPICT COUPLING YIELDING STRONG 
UPPER DIVERGENCE AND VVEL. ONLY DISCREPANCY BETWEEN GFS AND UKMET IS WITH
QPF WITH UKMET LIGHTER JUST UNDER .20 WHILE AVN/GFS NEARLY .33
ETA CUTS OFF ENERGY IN WEST WHILE AVN/GFS PROGRESSIVE AND DIGGY. BOTTOM LINE IS
CONFIDENCE IS VERY LOW. GLANCED AT 06Z RUNS OF META AND GFS.
META HAS JUMPED WELL NORTH WITH QPF INTO MUCH OF EASTERN IA AND NORTHWEST AND
WEST CENTRAL IL. QPF NEARLY .70 WHICH LOOKS WAY TOO AGGRESSIVE GIVEN
PRESENCE OF CONFLUENT UPPER FLOW...THUS BELIEVE .20 TO .25 MORE REASONABLE.
WITH SNOW TO WATER RATIOS AT 12:1 OR SO...LOOKING AT SOLID ADVISORY EVENT
WITH AMOUNTS OF 3-5 INCHES WITH 6 INCHES POSSIBLE. AVN/GFS TIME SECTS 
SHOW PRESENCE OF EPV INDICATING ELEVATED INSTABILITY...THUS CONVECTIVE BANDS 
WITH LOCALLY HIGHER AMOUNTS. GIVEN SUCH LARGE DISCREPANCIES IN
MODELS...AND FACT THAT BULK OF ACCUM SNOWS LIKELY TUE AFTN-TUE NIGHT WILL
HOLD OFF ON HEADLINES AND LET DAY CREW TAKE ANOTHER LOOK. 
HOPEFULLY 12Z RUNS WILL OFFER BETTER AGREEMENT. WILL HIGHLIGHT SIGNIFICANT
SNOW POTENTIAL IN MORNING HWO. 

ANY SNOW COVER WILL HAVE BIG IMPACT ON TEMPS IN EXTENDED. MADE LITTLE CHANGES
ATTIM DUE TO BIG MODEL DISCREPANCIES. 

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

$$

05