FXUS63 KMPX 251217
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
617 AM CST WED NOV 25 2009

UPDATED FOR 12Z AVIATION DISCUSSION BELOW...

.DISCUSSION...

MAIN FORECAST CONCERNS ARE IN THE NEXT 24 TO 36 HRS AND CENTER 
AROUND PRECIP TYPE AND AMOUNTS AS WELL AS WINDS. EARLY MORNING WATER 
VAPOR IMAGERY SHOWS THE UPPER LOW THAT BROUGHT DREARY WEATHER THE 
PAST FEW DAYS NOW ROTATING EASTWARD ACROSS NORTHERN ILLINOIS AND 
INDIANA. ANOTHER DEEP TROUGH IS WORKING SOUTHEASTWARD ACROSS NORTH 
DAKOTA TOWARDS MINNESOTA. FURTHER WEST...RIDGING HAS AMPLIFIED OVER 
EASTERN BRITISH COLUMBIA AND WESTERN ALBERTA IN RESPONSE TO A DEEP 
UPPER LOW JUST OF THE B.C. AND ALASKA COASTS. AS MENTIONED 
ABOVE...THE MOST ACTIVE PERIOD OF THE FORECAST WILL BE OVER THE NEXT 
24 TO 36 HRS WITH A RESPITE ARRIVING FOR THANKSGIVING AND CONTINUING 
INTO THE WEEKEND. AFTER THAT...THE PATTERN LOOKS TO BECOME MORE 
ACTIVE AGAIN...BUT THERE IS ONLY SUPPORT FOR LOW POPS INTO EARLY 
NEXT WEEK.

TODAY AND TONIGHT...THE FORECAST AREA IS IN THE COL AREA BETWEEN THE 
UPPER LOW TO THE EAST AND THE APPROACHING UPPER LOW TO THE WEST. A 
NARROW AREA OF CLEAR SKIES HAS DEVELOPED BETWEEN THE TWO SYSTEMS 
ACROSS THE CENTRAL PART OF THE AREA AND WILL CONTINUE TO TRANSLATE 
EASTWARD. A BAND OF MID LEVEL CONVERGENCE/FRONTOGENESIS CONTINUES TO 
FORCE A BAND OF RAIN WHICH IS NOW RIGHT ALONG THE MN/WI BORDER AND 
SLOWLY MOVING EAST. THIS WILL CONTINUE EAST THIS MORNING BUT WILL 
LIKELY BEGIN TO DECREASE IN COVERAGE/INTENSITY THROUGH MID MORNING. 
RADAR MOSAIC SHOWS RAIN/SNOW SHOWERS MOVING ACROSS SOUTHEASTERN 
NORTH DAKOTA INTO WEST CENTRAL MINNESOTA AS THE UPPER TROUGH 
APPROACHES. OVERALL THIS SYSTEM WILL TRACK A BIT FURTHER WEST THAN 
FORECAST YESTERDAY. THIS WILL HAVE AN IMPACT ON THERMAL PROFILES AND 
THEREFORE PRECIP TYPE THROUGH TONIGHT. PRECIPITATION WILL SPREAD 
INTO THE WESTERN CWA OVER THE NEXT FEW HOURS. WITH THE LOW TRACKING 
SOUTHEASTWARD ACROSS FAR SOUTHWEST MN... AREAS ALONG AND SOUTH OF 
THE MN RIVER VALLEY WILL BE IN POSITION TO TO RECEIVE THE STEADIEST 
PRECIPITATION THIS MORNING...WITH RADAR TRENDS SUPPORTING THIS. DRY 
AIR WILL WRAP INTO THE LOW WITH TIME THIS MORNING SO SIZABLE BREAKS 
IN THE PRECIPITATION ARE EXPECTED ACROSS THE SOUTHWEST AND SOUTH 
AROUND MIDDAY. THE UPPER LOW WILL BECOME BETTER ORGANIZED AS IT 
DIVES INTO CENTRAL IOWA EARLY THIS AFTERNOON. FORCING WILL INCREASE 
AS THIS OCCURS WITH INCREASED Q-VECTOR CONVERGENCE SHOWING UP IN THE 
MID LEVELS AND POTENTIAL VORTICITY ANOMALY TAKING ON MORE DEFINITION 
OVER SOUTHERN MINNESOTA. THEREFORE EXPECT THE BEST COVERAGE AND 
HIGHEST INTENSITY PRECIPITATION THIS AFTERNOON AND CONTINUE INTO THE 
EARLY EVENING. THE FAVORED AREA WILL BE THE SOUTHEAST THIRD OR SO OF 
THE CWA ALONG AND EAST OF I-35 AND SOUTH OF I-94 OR FROM THE 
SOUTHERN TWIN CITIES METRO SOUTH-SOUTHWEST TO WASECA AND ALBERT LEA 
AND FROM THE SOUTHERN TWIN CITIES SOUTHEAST TO RED WING AND TOWARDS 
EAU CLAIRE. OVERALL THE HEAVIEST PRECIP WILL BE JUST SOUTHEAST OF 
THE CWA.

PRECIPITATION TYPE IS THE NEXT ISSUE. AS MENTIONED ABOVE...WITH
THE LOW FURTHER WEST THE COLD AIR WILL NOT ADVANCE AS FAR EAST AS
QUICKLY AND WARM AIR WRAPPING AHEAD OF THE LOW WILL BE ABLE TO
WORK WESTWARD INTO THE EASTERN HALF OF THE CWA TODAY. MID LEVEL
TEMPS/THICKNESSES ARE COLD ENOUGH TO SUPPORT SNOW BUT MODEL
FORECAST SOUNDINGS SHOW MUCH WARMER LOW LEVEL AIR THAN RECENT
DAYS. WILL STICK WITH SNOW ACROSS THE WESTERN QUARTER TO THIRD OF
THE AREA THIS MORNING BASED ON CURRENT TRENDS. WITH COLUMN TEMPS
WARMER TO THE EAST RAIN/SNOW MIX WILL BE MORE
PREVALENT...ESPECIALLY THIS MORNING ACROSS EAST CENT MN WITH
CONTINUED DRIZZLE/LIGHT RAIN ACROSS WEST CENT WI IN CONJUNCTION
WITH THE BAND NOTED ABOVE. WITH FORCING INCREASING THIS AFTERNOON
PRECIPITATION INTENSITY MAY BE JUST STRONG ENOUGH TO TRANSITION
PRECIP TO ALL SNOW ACROSS EAST CENT MN BY LATE AFTERNOON WHILE
RAIN WITH A MIX OF RAIN/SNOW AND POSSIBLY SOME ICE PELLETS WILL BE
UNDERWAY ACROSS WEST CENT WI WITH THE BETTER CHANCE FOR A MIX
COMING LATE IN THE AFTERNOON AND EARLY THIS EVENING. COLD AIR WILL
MAKE QUICKER FORWARD PROGRESS THIS EVENING BUT PRECIP WILL BE
WINDING DOWN. AS FAR AS SNOW ACCUMULATION GOES...THIS WILL BE
TOUGH BUT AN INCH OR SO WILL BE POSSIBLE WHERE SNOW IS MOST
PERSISTENT ACROSS SOUTH CENTRAL MN AND NORTHEASTWARD TOWARDS THE
FAR SOUTHERN TWIN CITIES METRO AND RED WING. SHOULD PRECIP BECOME ALL
SNOW EARLIER THAN CURRENTLY FORECAST THEN 2 INCH AMOUNTS ARE
POSSIBLE BUT THIS IS LOOKING LESS LIKELY. NORTHWEST WINDS WILL
INCREASE MARKEDLY IN THE WEST THIS MORNING BEFORE SPREADING
SOUTHEASTWARD. BASED ON THE PATH OF THE LOW AND EXPECTED PATH OF
HIGHER TROP PRESSURES THE STRONGEST WINDS WILL BE IN THE FAR
SOUTHWEST BUT ALL AREAS WILL BE BREEZY BY EVENING. STRONGEST
SUSTAINED WINDS OF 20 TO 25 MPH ARE EXPECTED FAR WEST WITH GUSTS
OVER 30 MPH.

THURSDAY THROUGH SATURDAY...THE UPPER LOW WILL BE MOVING ACROSS THE 
OHIO VALLEY THURSDAY MORNING. SFC HIGH PRESSURE WILL BE BUILDING 
EASTWARD INTO THE AREA WHILE THE WESTERN RIDGE PUSHES EASTWARD INTO 
THE DAKOTAS. IT WILL BE A MUCH COOLER DAY THAN THE AREA HAS SEEN IN 
A WHILE WITH HIGHS ONLY IN THE LOWER TO MID 30S THANKS TO H85 AIR IN 
THE -4 TO -6 C RANGE AND A BRISK NORTHWESTERLY WIND. WINDS WILL 
SLACKEN IN THE AFTERNOON THOUGH...AS THE SFC RIDGE AXIS REACHES THE 
FORECAST AREA. THE UPPER RIDGE WILL BECOME RE-ORIENTED OFF TO THE 
WEST RESULTING IN SLIGHTLY FLATTER UPPER FLOW OVERHEAD LOCALLY BUT 
WARM ADVECTION WILL STILL GET UNDERWAY THURSDAY NIGHT AHEAD OF A 
WEAK TROUGH. THIS LOOKS TO ONLY RESULT IN SOME INCREASED CLOUD COVER 
AND A REDUCED TEMPERATURE DECREASE INTO FRIDAY MORNING. A SHARPER 
UPPER RIDGE WILL CROSS THE AREA SATURDAY KEEPING DRY WEATHER IN 
PLACE. 

SATURDAY NIGHT THROUGH SUNDAY NIGHT...AN UPPER TROUGH WILL BE MOVING 
ACROSS SOUTHERN CANADA SATURDAY NIGHT BRINGING FALLING SFC PRESSURES 
AHEAD OF IT. MAIN LOW CIRCULATION WILL BE WELL OFF TO THE NORTH WITH 
A TROUGH AXIS EXTENDING SOUTHWARD INTO THE PLAINS. ENOUGH UPPER 
FORCING WILL BE IN PLACE TO SUPPORT SOME PRECIPITATION POTENTIAL 
TOWARDS SUNDAY MORNING BUT NOTHING SIGNIFICANT IS EXPECTED AT THIS 
TIME. MODEL DISAGREEMENT REMAINS WITH THE EVOLUTION AND PATH OF THE 
UPPER LOW INTO MONDAY. WILL KEEP THE GOING FORECAST AS IS FOR NOW 
BUT LOW POPS MAY BE NEEDED SUNDAY NIGHT AND MONDAY.  ..MDB..

&&

.AVIATION... /12Z TAF ISSUANCE/ 
AN UPPER LOW PRESSURE OVER THE UPPER MIDWEST...WILL WRING OUT SOME 
LIGHT SNOW OR RAIN TODAY AS THE SYSTEM MOVES SOUTHEAST OVER NORTHERN 
ILLINOIS BY THURSDAY MORNING. PRECEDING THE PRECIP BAND THAT WAS  
ASSOCIATED WITH THE UPPER LOW...AN AREA OF LIFR TO IFR WEATHER CONDS 
COVERED PARTS OF WEST CENTRAL WI AND EAST CENTRAL MN. SOME PARTIAL 
CLEARING AND IMPROVEMENT HAD OCCURRED OVER CENTRAL MN DURING THE 
OVERNIGHT AND MORNING HOURS. CONDS ARE EXPECTED TO DETERIORATE THIS 
MORNING OVER WESTERN MN..AND OVER EAST CENTRAL MN AND PARTS OF WEST 
CENTRAL WISCONSIN THIS AFTERNOON. WEATHER CONDS ARE EXPECTED TO 
IMPROVE TO VFR OR SKC OVER WEST CENTRAL AND CENTRAL MN THIS EVENING 
WITH MVFR FLYING CONDS LINGERING OVER WEST CENTRAL WISCONSIN DURING 
THE REMAINDER OF THE PERIOD.  SFC PRES GRADIENT WILL CONTINUE TO 
TIGHTEN OVER WESTERN HALF OF MN TODAY. EXPECT GUSTS TO AROUND 30 
KNOTS AT TIMES...ESPECIALLY WEST OF THE MINNESOTA RIVER VALLEY.  
WINDS DIMINISHING DURG THE EVENING/OVERNIGHT TONIGHT.   

&&

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

$$

MDB/JM