FXUS63 KMPX 220446
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1045 PM CST MON DEC 21 2009

.UPDATED FOR AVIATION DISCUSSION BELOW...

.DISCUSSION...

FIRST FORECAST PROBLEM TONIGHT IS BAND OF SNOW SETTING UP ACROSS
SOUTH CENTRAL MN. FAIRLY IMPRESSIVE ISENTROPIC LIFT SETTING UP ION
THE 290/295 SURFACE ACROSS THIS AREAS WITH UP TO 3 G/KG MOISTURE
TO WORK WITH. AROUND ONE QUARTER INCH QPF AND A LITTLE HIGHER IN
SOME SPOTS SHOULD YIELD SOME SNOW AMOUNTS UP TO 5 INCHES. SREF
DOES HAVE SOME LOW END PROBS OF A DENDRITIC GROWTH ZONE OF 50-100
MB OVER SOUTH CENTRAL MN INTO NE IOWA OVERNIGHT. THERE IS SOME
RISK THAT HIGHER SNOW AMOUNTS MAY BE NEEDED A LITTLE FATHER NORTH
THIS EVENING. THERE IS STILL A SMALL CHANCE OF FREEZING DRIZZLE ON
TUESDAY OR TUESDAY NIGHT AFTER THE FORCING MOVE AWAY FOR THIS
SYSTEM. 

OTHERWISE...THE TRENDS OF MODEL GUIDANCE FOR THE IMPENDING STORM
HAVE COME INTO SOME AGREEMENT. THE 12Z GFS ENSEMBLE MEMBERS NOW
HAVE A CLOSE CLUSTER OF TRACKS FROM NORTHEAST MISSOURI ACROSS
EASTERN IOWA INT SOUTHERN WI. THE ECMWF CONTINUES A SIMILAR TREND
OF LOW LEVEL FEATURES. THIS PLACES MUCH OF THE THE CWA IN HEAVY
SNOW ESPECIALLY FROM SW MN INTO EAST CENTRAL MN AND PARTS OF
WESTERN WISCONSIN. THE 200 MB FORECAST TEMP GRADIENT FROM THE
CENTRAL PLAINS INTO THE UPPER MISS VALLEY AND THE GREAT LAKES AND
THE IMPLIED PV ANOMALY TO OUR SOUTH..SUGGEST SOME FINAL SNOWFALL
TOTALS NEAR 20 INCHES IN SOME SPOTS WHICH COULD INCLUDE AMOUNTS
FROM TONIGHT. OTHER AREAS OF THE CWA COULD SEE 8 INCHES + FOR
TOTALS. THE GEFS IS ALSO STILL SHOWING A SIGNAL FOR HIGH
PRECIPITABLE WATER JUST TO OUR SOUTH...FOR THIS TIME OF YEAR AS
WELL. MAY NEED TO ADD SOME MIXED PRECIP OVER FAR SE MN AND WESTERN
WISCONSIN WHICH COULD CUT DOWN OF SNOW TOTALS. WILL GO AHEAD AND
ISSUE A WINTER STORMS WATCH FOR THE ENTIRE AREA...STARTING
WEDNESDAY AFTERNOON IN THE SOUTH CENTRAL...AND THE REST OF THE
AREA WEDNESDAY NIGHT. WILL CONTINUE THE WATCH THROUGH FRIDAY...BUT
HIGHLIGHTS MAY ULTIMATELY NEED TO BE EXTENDED BEYOND THAT EASTERN
AREAS. THIS IS REACHING OUT FOR A WATCH SCENARIO...THUS THE REASON
FOR THE INITIAL TIMING. THERE WILL LIKELY BE A FEW WAVES OF
FORCING FOR THIS EVENT WITH THE INITIAL WARM ADVECTION/ISENTROPIC
LIFT FOR WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT...AND THEN THE
DEEPENING OF THE SYNOPTIC SCALE SYSTEM OVER THE MISSOURI AREA.
THERE IS STILL A TREND FOR THE SYSTEM TO FILL AFTER BECOMING
STACKED UP WHILE MIGRATING OFF TO THE NORTHEAST. WE WILL STILL SEE
SNOW WITH THIS BEYOND CHRISTMAS DAY BUT LIGHTER AMOUNTS. LITTLE
DIURNAL RANGE IN TEMPS THOUGH MUCH OF THE PERIOD UNTIL ALONG ABOUT
CHRISTMAS DAY,

&&

.AVIATION.../06Z TAF ISSUANCE/ 

MAIN CONCERN FOR THE REMAINDER OF THE NIGHT IS LIGHT SNOW MOVING 
ACROSS KRWF-KMSP-KRNH REGION.  BEST SATURATION NOW MOVING ACROSS THE 
CWA NOW-12Z TUE.  WILL MENTION SOME IFR CONDS OVER THIS REGION OF 
THE FA.  DRIER AIR TO THE EAST AND NORTH WILL LIMIT CIGS TO MVFR.
MAY SEE SOME BKN CIGS OVER THE FAR NORTHEAST FA DURING TUE 
MORNING...BUT WILL MAINTAIN MVFR CIGS FOR THE MOST PART ACROSS THE 
ENTIRE AREA.  WEAK LIFT INDICATED ON ISENTROPIC CHARTS COULD 
CONTINUE FLURRY THREAT INTO MUCH OF THE DAY.  SHOULD BE WIDELY SCT 
HOWEVER SO WILL LEAVE OUT OF TAF SITES FOR NOW.  CIGS MAY DROP OFF 
TO IFR AGAIN TUE NIGHT AS LIFT INTENSIFIES AHEAD OF DEVELOPING 
STORM.  EASTERLY SFC FLOW WILL CONTINUE THOUGH THE 
PERIOD...GENERALLY LESS THAN 12 KTS DURING THE PERIOD.
&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY 
     AFTERNOON FOR ANOKA-BENTON-BROWN-CARVER-CHIPPEWA-CHISAGO-
     DAKOTA-DOUGLAS-GOODHUE-HENNEPIN-ISANTI-KANABEC-KANDIYOHI-
     LAC QUI PARLE-LE SUEUR-MCLEOD-MEEKER-MILLE LACS-MORRISON-
     NICOLLET-POPE-RAMSEY-REDWOOD-RENVILLE-RICE-SCOTT-SHERBURNE-
     SIBLEY-STEARNS-STEVENS-SWIFT-TODD-WASHINGTON-WRIGHT-YELLOW 
     MEDICINE.

     WINTER WEATHER ADVISORY UNTIL 6 AM CST TUESDAY FOR BROWN-MARTIN-
     NICOLLET-REDWOOD-WATONWAN-YELLOW MEDICINE.

     WINTER WEATHER ADVISORY UNTIL 9 AM CST TUESDAY FOR BLUE EARTH-
     FARIBAULT-FREEBORN-STEELE-WASECA.

     WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY 
     AFTERNOON FOR BLUE EARTH-FARIBAULT-FREEBORN-MARTIN-STEELE-
     WASECA-WATONWAN.

WI...WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY 
     AFTERNOON FOR BARRON-CHIPPEWA-DUNN-EAU CLAIRE-PEPIN-PIERCE-
     POLK-RUSK-ST. CROIX.

&&

$$

JPR/DWE