FXUS63 KMPX 050452
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1052 PM CST FRI DEC 4 2009

.DISCUSSION...

MAIN CONCERN DURING THE SEVEN DAY FORECAST REVOLVES AROUND A
POTENTIAL SIGNIFICANT SNOW EVENT FOR PORTIONS OF THE FORECAST AREA
TUESDAY INTO WEDNESDAY. MORE ON THAT IN A BIT. 

IN THE SHORT TERM...FLURRIES AND SNOW SHOWERS CONTINUE TO STREAM
SE ACROSS MUCH OF THE FA AHEAD OF A SHORT WAVE ENTERING NW MN.
THIS FEATURE WILL MOVE ACROSS THE CWA TONIGHT. BEST LAYER
MOISTURE...ISENTROPIC OMEGA AND 400 MB PV ADVECTION IS SHOWN
ACROSS WEST CENTRAL WI EARLY TONIGHT. THIS IS ALSO WHERE THE SREF
PROBABILITY FOR MEASURABLE PRECIP IS HIGHEST. WILL USE SCT SNOW
SHOWERS FOR THIS AREA WITH UP TO A HALF INCH OF ACCUMULATION. KEPT
FLURRIES ACROSS THE MN CWA FOR MUCH OF THE NIGHT. A WEAK RIDGE OF
HIGH PRESSURE ACROSS THE EASTERN DAKOTAS WILL MOVE IN OVERNIGHT. A
DECREASE IN CLOUDINESS IS EXPECTED AS A RESULT WITH MORE OVERNIGHT
LOWS IN THE SINGLE DIGITS ACROSS MUCH OF THE MN CWA.

THE LOW LEVEL FLOW WILL TURN MORE SOUTHERLY ON SATURDAY AHEAD OF A
LOW PRESSURE SYSTEM FORMING OVER THE NORTHERN PLAINS. THE SURFACE
LOW IS IN RESPONSE TO AN UPPER LEVEL LOW DROPPING SE FROM BRITISH
COLUMBIA. A HALF WAY DECENT DAY IS EXPECTED TOMORROW WITH
AFTERNOON HIGHS IN THE MIDDLE TO UPPER 20S. CLOUDINESS WILL BEGIN
TO THICKEN ACROSS THE NORTHERN PORTIONS OF THE FA DURING THE
AFTERNOON AS MID FRONTOGENESIS BEGINS. 

THE SURFACE LOW WILL SLIDE OFF TO OUR EAST SATURDAY NIGHT AND
SUNDAY AS THE UPPER LOW TO OUR WEST SHEARS APART. A SHORT WAVE FROM
THE UPPER LOW IS NOW PROJECTED TO PASS FURTHER SOUTH OF US SUNDAY
NIGHT AND EARLY MONDAY BY ALL OF THE DETERMINISTIC RUNS TODAY.
THIS HAS NOW PUSHED THE BULK OF THE PRECIPITATION INTO THE FAR
SOUTHERN REACHES OF MN FOR SUNDAY NIGHT. THE GFS ENSEMBLE FOR THE
PAST TWO DAYS HAS BEEN SHOWING VERY LOW PROBABILITIES FOR
MEASURABLE PRECIPITATION TO OUR SOUTH AND THIS IS STARTING TO
LOOK MORE AND MORE LIKE THE CASE. WITH THE SYSTEM STILL 48 TO 60
HOURS AWAY...WAS CAREFUL TO NOT LOWER POPS TO MUCH OVER SOUTHERN
MN. MAIN CHANGE WAS TO ELIMINATE POPS ACROSS CENTRAL AREAS OF
MN...ESPECIALLY FROM KSTC TO KAXN ON NORTH.

IN THE WAKE OF THIS FEATURE ON MONDAY...A 1044 MB HIGH IS
FORECAST OVER SOUTHERN ALBERTA WITH SUBSTANTIAL RIDGING ACROSS THE
NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY. WHAT THIS TRANSLATES
INTO IS MORE LOW LEVEL COLD AIR FOR THE BEGINNING OF NEXT WEEK
WITH 850 MB TEMPERATURES VERY SIMILAR TO WHAT WE HAVE HAD THE PAST
TWO DAYS. HENCE...MORE LOWS IN THE SINGLE DIGITS WITH HIGHS IN THE
TEENS AND LOWER 20S.

BEYOND MONDAY...A STRONG SHORT WAVE IS SHOWN BY THE ECMWF...GFS
AND CANADIAN TO PASS ACROSS THE FOUR CORNERS AREA ON TUESDAY AND
REACH THE TN AND OH VALLEYS ON WEDNESDAY. TIMING AND DEPTH IS NOT
TOO BAD FOR A FEATURE 120 HOURS OUT. SURFACE LOW PRESSURE IS
PROJECTED FROM THE OK PANHANDLE TO IN/OH FROM TUESDAY INTO
WEDNESDAY. THIS PLACES THE SOUTHEAST HALF OF THE FORECAST AREA IN
A FAVORABLE AREA FOR SNOW ACCUMULATION...ALTHOUGH THE ECMWF AND
CANADIAN WOULD FAVOR THE HEAVIEST SNOW WELL TO OUR SOUTH WHILE
THE GFS IS A FURTHER NORTH AND WOULD FAVOR AREAS TO THE SOUTH AND
EAST OF THE TWIN CITIES. PLENTY WILL CHANGE BETWEEN NOW AND THEN
BUT FOR NOW HAVE RAISED POPS INTO THE LIKELY CATEGORY FOR TUESDAY
NIGHT TO THE EAST AND SOUTH OF THE TWIN CITIES WITH CHANCE POPS TO
THE WEST AND NORTH. 

THE FORECAST PERIOD ENDS WITH HIGH PRESSURE BUILDING IN FOR
THURSDAY AND FRIDAY WITH MORE BELOW NORMAL TEMPERATURES FOR BOTH
DAYS. 

&&

.AVIATION.../06Z TAF ISSUANCE/ 

MAIN FORECAST CONCERNS DEAL WITH MVFR CEILINGS IN THE FIRST 6 HRS
AS PERSISTENT MOIST RH FIELDS BELOW 85H AND THE CONTINUED LIFT
ASSOCIATED WITH THE DEPARTING UPPER SYSTEM ACROSS THE NORTHERN GREAT
LAKES...REMAINS NEAR THE AREA. STC/RNH/MSP/EAU WILL LIKELY SEE
SOME 2500' CEILINGS WITH VSBY AROUND 5SM AT THE WORSE. MOST AREAS
SHOULD BEGIN TO SEE VFR CEILINGS AFTER 09Z...WITH CEILINGS AOA
5000' BY 12Z. WEAK SFC LOW MOVING ACROSS SOUTHERN MN TODAY WITH
AID IN THE WINDS BACKING TO THE SE OVERNIGHT...AND TO THE E/NE BY
MID MORNING...THEN TO THE N/NW BY LATE TOMORROW AFTN. WIND SPEEDS
SHOULD BE LOW AND UNDER 10 KTS. ..JLT..

&&

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

$$

RAH/JLT