FXUS63 KMPX 041809
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1209 PM CST FRI DEC 4 2009

.UPDATE...

ADDED AVIATION DISCUSSION FOR 18Z TAFS BELOW...

&&

.PREVIOUS DISCUSSION...

915 AM CST UPDATE

RADAR AND SFC OB TRENDS SHOW A LARGE AREA OF SNOW SHOWERS ACROSS
THE NORTHEASTERN TWO-THIRDS OF THE CWA THIS MORNING. SATELLITE
SHOWS COLD UPPER VORTEX ROTATING OVER ONTARIO AND THE UPPER GREAT
LAKES WITH A SERIES OF WEAK WAVES ROTATING AROUND IT. CONTINUED
Q-VECTOR CONVERGENCE AND DEEP LAYER OF MOISTURE ASSOCIATED WITH A
PASSING VORT MAX SUGGEST THAT SNOW SHOWERS WILL CONTINUE INTO THE
AFTERNOON WITH THE VERY COLD AIR DOING AN EFFICIENT JOB OF
WRINGING OUT THE MOISTURE. ADDITIONAL FLUFFY ACCUMULATIONS UP TO A
HALF OR ONE INCH ARE EXPECTED ALONG THE INTERSTATE 94 CORRIDOR
WITH LESSOR AMOUNTS AND LESSER SNOW SHOWER COVERAGE TO THE SOUTH
AND WEST OF THE INTERSTATE. THE BULK OF THE ACTIVITY WILL PIVOT EAST
WITH TIME THIS AFTERNOON BUT SCATTERED FLURRIES AND ISOLATED SNOW
SHOWERS WILL CONTINUE ACROSS THE MN CWA ONCE THE MORE WIDESPREAD
ACTIVITY IS MORE FOCUSED OVER WEST CENT WI.  ..MDB..

EARLY MORNING DISCUSSION /ISSUED 345 AM CST FRI DEC 4 2009/

FORECAST CONCERN NEAR TERM IS THE CONTINUING THREAT OF SNOW
SHOWERS OVER MAINLY THE NORTHERN PORTION OF THE CWA DURING THE
DAY. MODELS CONTINUE TO TREND WHAT APPEARS TO BE VIGOROUS VORT
MAXIMA ROTATING VCNTY OF LAKE WINNIPEG THIS MORNING. TREND OF THE
NAM_WRF WAS TO INTENSIFY IT A BIT AS IT MOVES SOUTH SOUTHEAST
DURING THE AFTERNOON/EVENING. SOME DECENT LIFT/Q VECTOR
CONVERGENCE MOVES OVER THE NORTHEAST CWA THIS AFTERNOON/EVENING.
THIS IS ENOUGH FOR CHANCE POPS OVER THE NORTHERN AREA FOR MORE
SNOW SHOWERS TODAY. CLOUDS DID BREAK OPEN OVER THE SOUTHWEST IN
THE WAKE/SUBSIDENCE OF THE PREVIOUS SHORT WAVE. THIS PROVIDED NICE
TEMP DROP IN LIGHTLY SNOW COVERED REGION OF THE SOUTHWEST. SHOULD
SEE CLOUDS MOVE BACK IN EARLY THIS MORNING AS NEXT WAVE
APPROACHES. SOME WEAK CAA CONTINUES INTO THIS MORNING AND WITH
EXPECTED CLOUDS...LITTLE RISE IN TEMPERATURES EXPECTED. WENT WITH
A COLDER NAM GUIDANCE TEMPERATURES CONSIDERING TRAJECTORY OF
AIRMASS FROM YESTERDAY.

SYSTEM EXITS TO THE EAST OF THE AREA OVERNIGHT. SHOULD SEE SOME
CLEARING OVER THE WESTERN AND CENTRAL CWA DURING THE NIGHT. CLOUDS
MAY HANG INTO WC WI THROUGH THE NIGHT AS SFC RDG BUILDS INTO THE
WESTERN CWA. UNCLEAR HOW MUCH CLOUD COVER WILL BE AROUND SAT AND
SUNDAY AS TROUGH SHEARS OFF TO THE EAST. TEMPERATURES WILL BE
DE PENDANT OF CLOUD COVER INTO SUNDAY...SO WENT CLOSE TOM MAV
NUMBERS FOR NOW. MODELS DIVERGE SOMEWHAT ON HANDLING OF NEXT SHORT
WAVE TROUGH FOR SUN NIGHT INTO MONDAY. GFS HOLDS THE WAVE A BIT
FARTHER SOUTH THAN PREVIOUS RUNS...WITH THE COLD SFC HIGH WINNING
OUT ACROSS THE AREA. THE 00Z NAM_WRF AND 00Z ECMWF CONTINUE TREND
OF CLIPPING THE FAR SOUTHERN CWA WITH THIS SYSTEM. WILL TRIM POPS
A BIT TO THE NORTH BUT CONTINUE THE CHANCE POPS OVER THE FAR
SOUTHERN CWA. 

LONGER TERM...MODELS HAVE BEEN TRENDING TOWARD DEVELOPMENT OF
SIGNIFICANT LONG WAVE TROUGH OVER THE NATIONS MIDSECTION TOWARD
MIDWEEK. 00Z RUNS CONTINUE THE TREND OF SIGNIFICANT CYCLOGENESIS
NEAR THE CO/OK PANHANDLE REGION LATE TUE AND LIFTING NORTHEAST TO 
SOUTHERN LK MICHIGAN REGION BY WED MORNING. THIS TRACK WOULD
AFFECT MAINLY OUR SOUTHERN CWA AS THE LOW TRACKS SOUTH AND EAST.
THE HEAVIER SNOWS WOULD CLIP OUR SOUTHERN CWA WITH THE HEAVIEST SNOW
BAND OVER IOWA AND WI. THIS COULD BE OUR FIRST SIGNIFICANT STORM
OF THE SEASON AND WILL HIGHLIGHT THIS THREAT IN THE HWO.

&&

.AVIATION.../18Z TAF ISSUANCE/ 

UPPER LEVEL LOW PRESSURE CONTINUES TO BRING SNOW SHOWERS TO ALL
BUT KRWF THIS AFTERNOON. CEILINGS AND VISIBILITY ARE HIGHLY
VARIABLE WITH CIGS PRIMARILY MVFR AND VISIBILITY MOSTLY VFR
OUTSIDE OF SNOW SHOWERS BUT IFR/MVFR IN SNOW SHOWERS. LIGHT FLUFFY
ACCUMULATIONS CONTINUE UNDER THE MORE INTENSE SNOW SHOWERS. SNOW
SHOWERS WILL DIMINISH FROM WEST TO EAST LATE THIS AFTERNOON AND
EARLY THIS EVENING. EXPECT CEILINGS TO IMPROVE TO VFR FROM WEST TO
EAST THIS EVENING AND OVERNIGHT AS DRIER LOW LEVEL AIR MOVES IN.
SCATTERED LOW CLOUDS MAY DEVELOP SATURDAY MORNING. WEST SOUTHWEST
WINDS WILL CONTINUE THIS AFTERNOON BEFORE BECOMING SOUTHERLY
TONIGHT THEN SOUTHEASTERLY SATURDAY MORNING.

KAXN...LIGHT SNOW CONTINUES BUT COVERAGE WILL BE DECREASING OVER
THE NEXT FEW HOURS LEADING TO IMPROVING VISIBILITY. MVFR CEILINGS WILL
CONTINUE WITH IMPROVEMENT TO VFR EXPECTED BY EARLY THIS EVENING.
MID AND HIGH CLOUDS WILL REMAIN OVER THE AREA TONIGHT.

KSTC...LIGHT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON.
EXPECT VISIBILITY PRIMARILY IN THE 3 TO 5 SM RANGE IN -SN BUT A
BRIEF DROP TO 2SM REMAINS POSSIBLE. MVFR CIGS WITH VARIABLE BASES WILL
CONTINUE INTO EARLY EVENING WITH A SLIGHT INCREASE IN LOWEST BASES
FROM 1500 FT TO AROUND 2500 FT LATE THIS AFTERNOON.

KRWF...VFR LOOKS TO PREVAIL WITH MVFR CIGS HELD OFF TO THE NORTH
AND EAST. SOME LIGHT SNOW REMAINS POSSIBLE BUT VISIBILITY IS
EXPECTED TO REMAIN ABOVE 6 SM IF THIS OCCURS.

KMSP...VARIABLE CLOUD BASES WILL CONTINUE THROUGH THE AFTERNOON
WITH CIGS PRIMARILY ABOVE 1700 FT WITH PERIODIC DIPS TO AROUND
1500 FT AS MORE INTENSE SNOW SHOWERS PASS. VISIBILITY WILL BE
HIGHLY VARIABLE AS WELL WITH VALUES PRIMARILY AROUND 6SM WITH
DROPS TO 3 OR 4SM WITH SNOW SHOWERS WITH A BRIEF 2SM POSSIBLE.
CEILINGS ARE EXPECTED TO IMPROVE TO ABOVE 3000-4000 FT EARLY THIS
EVENING AS THE SNOW TAPERS OFF.

KEAU...VARIABLE MVFR CIGS BETWEEN 1500 AND 3000 FT WILL CONTINUE
AS SNOW SHOWERS INCREASE IN COVERAGE AND INTENSITY EARLY THIS
AFTERNOON. VISIBILITY WILL BE VARIABLE AND LIKELY DROP TO AROUND
2SM FOR SHORT TIMES THIS AFTERNOON. VFR CONDITIONS WILL TAKE A
LITTLE LONGER TO EXIT BUT EXPECT THAT VFR CONDITIONS WILL RETURN
LATE THIS EVENING.

KRNH...1500 TO 2500 FT CEILINGS WILL CONTINUE AS WILL SNOW
SHOWERS. VISIBILITY IS EXPECTED TO FALL TO 3 OR 4SM IN THE MORE
INTENSE SNOW SHOWERS WITH DECREASES TO AROUND 2SM POSSIBLE AT TIMES.
1500 FT BASES WILL BE LESS LIKELY BY LATE AFTERNOON WITH PRIMARILY
2500 FT BASES EXPECTED AT THAT TIME. VFR IS FORECAST TO RETURN
THIS EVENING AND CONTINUE THROUGH THE PERIOD.  ..MDB..

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

$$

DWE/MDB