FXUS63 KMPX 040453
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1053 PM CST THU DEC 3 2009

.DISCUSSION...

TEMPERATURES AT OR BELOW SEASONAL VALUES ALONG WITH BOUTS OF
SNOW/FLURRIES WILL BE THE RULE OVER THE NEXT SEVEN DAYS AS A
RATHER VIGOROUS UPPER AIR PATTERN OCCURS OVER NORTH AMERICA.

FIRST WEATHER MAKER IS A LOW/MID LEVEL CIRCULATION OVER SOUTH
CENTRAL MN. THIS FEATURE IS DRIFTING SLOWLY SOUTH ON RADAR. SNOW
WILL CONTINUE OVER SOUTH CENTRAL MN FOR THE REST OF THE AFTERNOON
THEN DIMINISH THIS EVENING. FLURRIES WILL BE COMMON ACROSS THE
AREA TONIGHT AS A COLD CYCLONIC FLOW OCCURS. 

AN UPPER LOW NOW OVER NORTHERN ONTARIO WILL DRIFT SOUTH TOWARD MN
ON FRIDAY. LAYER MOISTURE WILL INCREASE ONCE AGAIN AHEAD OF A
SHORT WAVE ROTATING ACROSS THE CWA DURING THE DAY. LAYER Q-VECTOR
CONVERGENCE INCREASES FROM THE NORTH DURING THE DAY ALONG WITH AN
INCREASE IN PV. CHANCES FOR SNOW SHOWERS FOR CENTRAL MN AND MUCH
OF WEST CENTRAL WI STILL LOOK GOOD WITH FLURRIES TO THE SOUTH.

A PERIOD OF DRY WEATHER IS THEN ANTICIPATED FOR SATURDAY AND
SATURDAY NIGHT. THEN THE FUN BEGINS FROM SUNDAY ONWARD AS A SERIES
OF SHORT WAVES HEAD OUR WAY FROM THE PACIFIC NORTHWEST. THE FIRST
ONE WILL DRIVE AN AREA OF ACCUMULATING SNOW PRIMARILY ACROSS
NEBRASKA AND IOWA WITH SOUTHERN MN BEING ON THE NORTHERN FRINGE.
AT LEAST THAT IS THE IDEA FROM THE ECMWF WHICH HAS BEEN PRETTY
CONSISTENT WITH THIS SYSTEM FOR SEVERAL DAYS NOW. THE GFS ON THE
OTHER HAND HAS TRENDED MUCH FATHER NORTH WITH THE SE HALF OF THE
CWA IN THE PATH FOR ACCUMULATING SNOW SUNDAY NIGHT. HOWEVER...THE
12Z GFS ENSEMBLE PROBABILITIES FOR .05 INCHES IN 12 HOURS IS
BARELY 20 PERCENT ACROSS FAR SOUTHERN MN. HENCE...CONTINUED WITH
THE ECMWF AND ONLY CHANCE POPS FOR SUNDAY AND SUNDAY NIGHT WITH
THE BEST CHANCE NEAR THE IOWA BORDER. 

SOME FLURRIES MAY LINGER ON MONDAY IN THE WAKE OF THIS
SYSTEM...ESPECIALLY OVER WEST CENTRAL WI. OTHERWISE...COLD HIGH
PRESSURE WILL MOVE IN FOR MONDAY NIGHT AND PART OF TUESDAY. 

THINGS THEN GET PRETTY INTERESTING AFTER THAT AS A RATHER LARGE
DISCREPANCY DEVELOPS BETWEEN THE ECMWF AND THE GFS WITH THE NEXT
SHORT WAVE APPROACHING FROM THE WEST FOR TUESDAY NIGHT AND
WEDNESDAY. DP/DT SHOWS THAT ALTHOUGH BOTH MODELS ARE SLOWING THE
EASTWARD ADVANCEMENT OF THE SHORTWAVE...THE ECMWF NOW HAS A CLOSED
UPPER LOW NEAR THE IA/MN BORDER WEDNESDAY MORNING WITH SURFACE LOW
PRESSURE OVER NORTHERN IL. THE GFS REMAINS WITH AN OPEN WAVE WITH
THE SURFACE LOW OVER KY. A CHECK OF THE GFS ENSEMBLE SHOWS THE LOW
NEAR INDIANAPOLIS. THE GFS ENSEMBLE PROBABILITIES FOR MEASURABLE
PRECIP ARE ALSO PRETTY HIGH TUESDAY AFTERNOON/NIGHT OVER THE SE
HALF OF THE CWA. THEREFORE...THE CHANCE FOR SNOW WAS
INCREASED/EXPANDED A BIT ACROSS THE SOUTHERN HALF OF THE CWA...BUT
MUCH UNCERTAINTY EXISTS. 

AS PREVIOUSLY MENTIONED...TEMPERATURES...LOWS AND HIGHS...WILL BE
AT OR BELOW SEASONAL VALUES. MAIN CONCERN IS TONIGHT AND FRIDAY
NIGHT ACROSS WEST CENTRAL AND SOUTHWEST MN WHERE LOWS IN THE
SINGLE DIGITS ARE EXPECTED. HOPEFULLY IT WON'T GET COLDER BUT
SEVERAL INCHES OF SNOW HAVE OCCURRED TODAY HERE AND THERE IN THE
AFOREMENTIONED AREAS. HIGHS WILL ALSO STRUGGLE TOMORROW WITH THE
COLD POCKET OVERHEAD IN THE LOW LEVELS. HIGHS ONLY IN THE LOWER
20S EXPECTED CWA WIDE AND THIS MAY BE TOO OPTIMISTIC AS ONLY TEENS
OCCURRED OVER THE NORTH DAKOTA AND NORTHERN SOUTH DAKOTA. SIMILAR
TEMPERATURE PATTERNS WILL LIKELY OCCUR NEXT MONDAY NIGHT AND
TUESDAY.

&&

.AVIATION.../06Z TAF ISSUANCE/ 

MAIN AVIATION CONCERN IS TIMING OF NEXT -SN EVENT TODAY AND HOW
LOW TO DROP VSBYS. VSBYS HAVE BEEN MOSTLY VFR THIS EVENING...WHICH
SHOULD CONTINUE THROUGH MOST OF THE TAF SITES THRU 09/12Z...AXN/STC
WILL BEGIN TO SEE SLIGHTLY LOWER CEILINGS/VSBY AS THE NEXT WAVE
BEGINS TO AFFECT THIS REGION. 

CEILINGS HAVE BEEN PROBLEMATIC WHICH IS ANOTHER CONCERN LATER
TODAY AS MOISTURE LEVELS REMAIN HIGH BELOW 85H...AND ANY DIURNAL
HEATING WILL AID IN CLD DEVELOPMENT. IN ADDITION...ANOTHER WAVE
WILL BEGIN TO AFFECT THE TAFS BY LATE MORNING/AFTN WITH VSBYS AS
LOW AS 2SM...ESPECIALLY FOR STC/MSP/RNH/EAU WHERE BEST LIFT AND
DEEPER MOISTURE WILL RESIDE. 

HAVE CONTINUED MVFR CEILINGS FOR THE MOST PART...BUT THERE COULD
BE A TEMPORARY PERIOD OF IFR CEILINGS IF THE SNOWFALL IS LOCALLY
HEAVY. NOT ANTICIPATING ANYTHING TOO DRASTIC AS UPSTREAM
CONDITIONS IN SOUTH CENTRAL CANADA REMAIN MVFR...WITH BRIEF
PERIODS OF IFR VSBYS. AFT 00Z/05...CONDITIONS SHOULD GRADUALLY
IMPROVE AS DRIER AIR WILL BEGIN TO FILTER ACROSS THE DAKOTAS...AND
INTO WESTERN MN. ..JLT..

&&

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

$$

RAH/JLT