FXUS63 KMPX 301142
AFDMPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
542 AM CST MON NOV 30 2009
.DISCUSSION...
TEMPERATURES WILL BE THE MAIN FOCUS THIS FORECAST PERIOD FOLLOWED
BY PERIODIC LOW PRECIP CHANCES. AFTER A COOL AND BRISK SUNDAY
THINGS WILL START TO WARM UP BUT THIS WILL ONLY BE TEMPORARY AS A
LARGE SCALE TROUGH BECOMES ESTABLISHED OVER MOST OF CANADA AND THE
U.S. BY LATE WEEK...WITH EMBEDDED SHORTWAVE TROUGHS BRINGING
SURGES OF INCREASINGLY COLDER AIR. IN THE MEAN TIME...EARLY
MORNING WATER VAPOR IMAGERY SHOWS A LONGWAVE TROUGH EXTENDING FROM
JAMES BAY SOUTHWARD ACROSS THE WESTERN GREAT LAKES AND MID
MISSISSIPPI RIVER VALLEY WHILE A CUTOFF UPPER LOW CONTINUES TO
SETTLE SOUTHWARD OVER NORTHWESTERN MEXICO. FAIRLY FLAT UPPER
RIDGING EXTENDS NORTHWARD FROM OFF THE CALIFORNIA COAST INTO THE
PACIFIC NORTHWEST WHILE WEAKLY RIDGED FLOW IS IN PLACE ACROSS
SOUTHWESTERN CANADA AND BECOMING MORE ACTIVE. LOOKING A LITTLE
CLOSER...A SUBTLE VORT MAX APPEARS OVER NORTH CENTRAL SASKATCHEWAN
WITH A SHEARED TROUGH TO ITS SOUTH. THIS WILL IMPACT THE WEATHER
TODAY. NEXT FEATURE OF NOTE IS A CIRCULATION COMING ON SHORE OVER
FAR NORTHWESTERN BRITISH COLUMBIA WHICH WILL MOVE EASTWARD AND
AMPLIFY BRINGING THE FIRST SHOT OF MUCH COLDER AIR FOR THE MIDDLE
PART OF THE WEEK.
TODAY...FIRST CONCERN WILL BE SHEARED VORT MAX CROSSING THE AREA AS
LEADING EDGE OF FLAT RIDGE OUT TO THE WEST MOVES TOWARDS THE AREA
TODAY. STRONG WARM ADVECTION WILL ACCOMPANY THIS FEATURE AS WILL A
WEAK SFC TROUGH. NORTHERN AND EASTERN PORTION OF THE CWA WILL BE ON
THE SOUTHERN END OF BETTER FORCING. MID LEVEL FRONTOGENESIS
INCREASES LATE THIS MORNING AS THE WAA MOVES EASTWARD ACROSS THE
AREA AND FOCUSES FROM ABOUT LITTLE FALLS SOUTH TO THE INTERSTATE
94 CORRIDOR FROM ST. CLOUD TO EAU CLAIRE AND POINTS NORTH OF THE
INTERSTATE THROUGH THE AFTERNOON. 285K AND 290K ISENTROPIC SFCS
SHOW GOOD UPGLIDE WITH STRONG ADIABATIC OMEGA AND SUFFICIENT
SATURATION OVER THE AFOREMENTIONED AREAS AFTER 15Z. ONE CAVEAT
WILL BE GETTING THE COLUMN SATURATED ENOUGH TO ALLOW PRECIP TO
REACH THE GROUND BEFORE FORCING MOVES OFF TO THE EAST. THE FOCUS
FOR THE PRECIP WILL PRIMARILY BE JUST NORTH AND EAST OF THE CWA
BUT FEEL DESPITE THE FAST MOVING FORCING THERE IS ENOUGH SUPPORT
FOR AN INCREASE IN POPS WITH THE IDEA THAT A SEVERAL HOUR WINDOW
OF PRECIPITATION WILL DEVELOP/MOVE INTO THE NORTHERN CWA IN THE
VICINITY OF ALEXANDRIA OR LITTLE FALLS AND MOVE EASTWARD WHILE
EXPANDING SOUTHWARD TOWARDS ST. CLOUD...THE NORTHERN TWIN CITIES
METRO...NEW RICHMOND...TO DURAND WISCONSIN DURING THE EARLY/MID
AFTERNOON. THE WARMER AIR IS FORECAST TO ARRIVE MUCH MORE QUICKLY
THAN IT LOOKED LIKE YESTERDAY WHICH WILL IMPACT PRECIP TYPE
FORECAST. EXPECT SNOW AT THE ONSET AS THE COLUMN REMAINS BELOW
FREEZING BEFORE QUICKLY WARMING. MAGNITUDE OF FORCING AND THE
EXPECTATION OF WET BULB TEMPS REMAINING BELOW FREEZING DURING
START OF ANY PRECIP MIGHT BE ENOUGH TO SUPPORT SOME LIGHT
ACCUMULATIONS OF A COATING OR SO BEFORE RAIN MIXES IN AND POSSIBLY
EVEN TAKES OVER INTO MID AFTERNOON ACROSS AFFECTED PORTIONS OF THE
MN CWA AND WESTERN WI CWA. FAR NORTHEASTERN CWA FROM ABOUT RICE
LAKE TO BLOOMER MAY STAY SNOW THE ENTIRE TIME AND THEREFORE HAVE
THE BEST CHANCE OF HAVING A FEW TENTHS OF SNOW ACCUMULATE. TEMPS
WILL BE A CHALLENGE. WARM ADVECTION WILL BE IN PLACE BUT INVERSION
WILL HELP LIMIT MIXING TO 950 OR 925 MB ACROSS MOST OF THE AREA
WITH A BIT BETTER MIXING POTENTIAL SOUTHWEST. SOUTHWESTERLY WINDS
WILL INCREASE THROUGH THE DAY AND ALSO HELP TEMPS IN THE SOUTHWEST
WITH DOWNSLOPE COMPONENT. NORTHEASTERN CWA COUNTIES WILL LIKELY BE
HELD IN THE MID 30S WHILE THE SOUTHWEST WARMS INTO THE MID 40S.
CENTRAL AREAS INCLUDING THE TWIN CITIES SHOULD MAKE IT TO AROUND
40.
TONIGHT THROUGH WEDNESDAY...WINDS WILL SLACKEN THIS EVENING AS A
BRIEF PERIOD OF SFC RIDGING MOVES ACROSS. THE AFOREMENTIONED UPPER
TROUGH CURRENTLY MOVING ONSHORE OVER NORTHWEST BRITISH COLUMBIA WILL
DIG INTO NORTHERN NORTH DAKOTA BY TUESDAY MORNING. A SFC LOW WILL
DEEPEN AND MOVE ALONG THE INTERNATIONAL BORDER AND INTO NORTHERN
MINNESOTA DURING THE DAY TUESDAY. HAVE SEEN SOME CHANGES IN HOW THE
MODELS HANDLE THIS SYSTEM. GFS HAS HAD A STEADY SOUTHWARD TREND OVER
ITS LAST SEVERAL RUNS WITH THE 00Z/30TH RUN TAKING THE SFC LOW
ACROSS NORTHERN MINNESOTA FROM ABOUT DRAYTON TO SILVER BAY WITH
UKMET AND CANADIAN GEM TAKING A SIMILAR TRACK. ECMWF IS A BIT
FURTHER NORTH WITH ITS 12Z/29TH RUN BUT IS ACTUALLY JUST SOUTH OF
THE GFS TRACK ON THE 00Z/30TH RUN. THE 00Z NAM IS MUCH DIFFERENT
THAN THESE BRINGING THE LOW ACROSS SOUTHERN MINNESOTA AND WILL
DISCOUNT THIS SOLUTION AT THE MOMENT. PRESSURE OF THE SFC LOW IS
ALSO FORECAST TO BE HIGHER THAN PREVIOUS DAYS WITH LOWEST PRESSURE
AROUND 1000 MB. LOW/MID LEVEL WARM AXIS WILL SURGE INTO SOUTHERN MN
TUESDAY MORNING WITH H85 TEMPS OF 0C TO +6C. HIGHS WILL BE TOUGH AND
WILL BE DEPENDENT ON THE SPEED OF THE COLD FRONTAL PASSAGE. WITH THE
SHIFT SOUTH IN THE TRACK THE FRONT WILL CROSS SOONER AND NOW LOOKS
TO BE HALFWAY ACROSS THE AREA BY MIDDAY. WESTERN AREAS MAY SEE EARLY
HIGHS BEFORE COOLING IN THE AFTERNOON WITH SHARP COLD ADVECTION AND
BREEZY WEST TO NORTHWEST WINDS. THE FRONT LOOKS TO PASS DRY WITH THE
UPPER FORCING AND MOISTURE CENTERED ACROSS THE NORTHERN THIRD OF
MINNESOTA. THE PASSAGE OF THE UPPER TROUGH AXIS WILL OCCUR TUESDAY
NIGHT AND BRING A SECOND SURGE OF COLD AIR BRINGING H85 TEMPS DOWN
TO -10 TO -14C BY WEDNESDAY AFTERNOON. CYCLONIC FLOW...COLD
ADVECTION...AND STEEP LOW LEVEL LAPSE RATES WILL SUPPORT FLURRIES OR
LIGHT SNOW SHOWERS WEDNESDAY OVER MOST OF THE AREA.
WEDNESDAY NIGHT THROUGH FRIDAY NIGHT...LONGWAVE TROUGH WILL BE
FIRMLY ESTABLISHED OVER THE GREAT LAKES AND EASTERN U.S. WITH A
RIDGE OVER THE WEST. DECENT MODEL AGREEMENT ON ANOTHER TROUGH
ROTATING SOUTHWARD BRINGING EVEN COLDER AIR AND MORE CHANCES FOR
SNOW SHOWERS WEDNESDAY NIGHT THROUGH THURSDAY. THURSDAY STILL LOOKS
TO BE THE COLDEST DAY WITH HIGHS ONLY IN THE LOW TO MID 20S. MODEL
DIFFERENCES INCREASE INTO FRIDAY WITH REGARD TO WHAT HAPPENS WITH
THE UPPER FLOW PATTERN AND TIMING OF ANOTHER TROUGH AFFECTING THE
AREA. ..MDB..
&&
.AVIATION.../12Z TAF ISSUANCE/
LOW PRESSURE OVER LAKE WINNIPEG AT 12Z TO MOVE SE TO CTRL LAKE
SUPERIOR BY 00Z...SWINGING A COLD FRONT GRADUALLY THROUGH MN AND
WRN WI. THE ELEVATED WARM FRONT WITH THIS SYSTEM WILL BE THE MAIN
FOCUS FOR CLOUDS AND POSSIBLY LIGHT SNOW/RAIN ACROSS WRN WI. THIS
FEATURE IS CURRENTLY DRAPED FROM N TO S FROM NW MN TO CTRL MN. AS
THIS SHIFTS EAST...WIDESPREAD 4KFT TO 8KFT CIGS WILL BLANKET ERN
MN AND WRN WI INTO THIS AFTN. SOME LIGHT PRECIPITATION IS LIKELY
IN WRN WI. THIS PROBABLY WILL BE SNOW...ALTHOUGH THERE IS A NARROW
WINDOW AT FIRST WHERE IT COULD BE LIGHT RAIN. NO ACCUM OR IFR
CONDITIONS EXPECTED. WINDS TO BE FROM THE SW AND VEER TODAY WITH
THE PASSING OF THE DEVELOPING COLD FRONT. WINDS WILL BE GUSTY IN
WRN MN AS THE SYSTEM IS IN A GRADUAL DEEPENING PHASE. SUSTAINED
WINDS OF 12-15 KTS EXPECTED AT THE TAF SITES FROM 16Z OR 17Z
THROUGH LATE AFTN.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&
$$
MDB/MTF
