FXUS63 KMPX 060452
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1052 PM CST SAT DEC 5 2009

.UPDATE...

ADDED 06Z TAF DISCUSSION BELOW. 

&&

.DISCUSSION...

CONCERNS ARE MANY OVER THE NEXT SEVEN DAYS AS A COLD AND ACTIVE
WEATHER PATTERN DOMINATES. 

IN THE SHORT TERM...CLOUDINESS HAS BEEN INCREASING THIS AFTERNOON
AS MID LEVEL FRONTOGENESIS SPREADS SOUTH INTO CENTRAL MN AND
WESTERN WI. THIS IS AHEAD OF AN UPPER TROF MOVING EAST ACROSS THE
FA OVERNIGHT. THE NAM AND GFS ARE BOTH SHOWING SATURATION AND
ADIABATIC OMEGA DEVELOPING (285K) OVER SE MN AND WEST CENTRAL WI
EARLY TONIGHT AS LOW LEVEL WAA IS MAXIMIZED. SOME LOW AMOUNTS OF
QPF INDICATED BY THE NAM IN THIS AREA WITH VERY LOW PROBABILITIES
FOR MEASURABLE ON THE 15Z SREF. DECIDED TO INCLUDE SMALL CHANCES
FOR LIGHT SNOW THROUGH THE NIGHT FROM ALBERT LEA TO LADYSMITH ON
EAST.

SURFACE RIDGING WILL THEN DOMINATE ACROSS THE UPPER MISSISSIPPI
VALLEY ON SUNDAY WHILE A WEAK LOW PRESSURE SYSTEM BEGINS TO TAKE
SHAPE OVER THE SOUTHERN PLAINS. THE DETERMINISTIC RUNS OF THE
NAM...GFS...CANADIAN AND ECMWF REMAIN CONSISTENT AND POINT TO THE
LOW PASSING ACROSS NORTHERN MO AND IL SUNDAY NIGHT AND MONDAY. THE
BEST SATURATION AND FORCING IS STILL SEEN PASSING ACROSS FAR
SOUTHERN MN AND SOUTHERN WI DURING THE AFOREMENTIONED PERIODS. THE
MODEL RUNS ARE ALSO CONSISTENT ON KEEPING THE NORTHERN EXTENT OF
THE HUNDREDTH OF AN INCH LINE ACROSS THE SOUTHERN TWIN CITIES
METROPOLITAN AREA. THEREFORE...VERY MINIMAL POPS FOR THE
SOUTHERN TWIN CITIES SUNDAY NIGHT AND EARLY MONDAY INCREASING TO
CATEGORICAL POPS ALONG THE INTERSTATE 90 CORRIDOR. BASED ON QPF
AND SNOW RATIOS AROUND 14 TO 1...ARRIVED AT NEARLY 2 INCHES OF
ACCUMULATION BY MONDAY MORNING ALONG I-90 DECREASING TO TRACE
AMOUNTS NEAR A CANBY-TWIN CITIES-LADYSMITH LINE.

IN THE WAKE OF THIS SYSTEM EARLY ON MONDAY...MORE RIDGING WILL
DOMINATE ACROSS THE AREA AS A NEW LOW PRESSURE STORM SYSTEM
BEGINS TO TAKE SHAPE OVER THE SOUTHWESTERN UNITED STATES. THIS
LOW IS ALSO HANDLED WELL AGAIN TODAY BETWEEN THE GFS...CANADIAN
AND ECMWF. CURRENT PROJECTIONS SHOWS THE LOW OVER THE OK PANHANDLE
TUESDAY NIGHT WITH THE LOW REACHING THE CENTRAL GREATS BY LATE
WEDNESDAY. WHAT IS QUITE INTERESTING FOR US IS THAT ALTHOUGH THE
LOW IS PRETTY FAR SOUTH FOR A TYPICAL HEAVY SNOW EVENT...MUCH OF
THE CWA WILL BE ON THE WEST SIDE OF AN INVERTED SURFACE TROUGH.
THE DETERMINISTIC RUNS ARE SHOWING MID LEVEL FRONTOGENESIS FROM
WESTERN IA UP ACROSS THE TWIN CITIES TO NORTHERN WI. THE 285K
THETA SURFACES FROM THE VARIOUS SOLUTIONS ALL SHOW SATURATION
AND RATHER IMPRESSIVE ADIABATIC OMEGA SPREADING ACROSS THE SE HALF
OF THE CWA TUESDAY INTO EARLY WEDNESDAY. 

MIXING RATIOS ARE BETWEEN 1.5 G/KG OVER THE TWIN CITIES WITH 2
G/KG ACROSS SOUTH CENTRAL MN. THIS DOESN'T SEEM LIKE MUCH...BUT WE
WILL BE IN MODIFIED ARCTIC AIR. THE 12Z MREF PLUMES INDICATE
A MEAN OF 0.45 INCHES FOR THE TWIN CITIES TUESDAY AFTERNOON TO
WEDNESDAY AFTERNOON. USING THE AVERAGE GFS COBB SNOW RATIOS FOR
THIS PERIOD COMES TO 17. MULTIPLYING THE TWO RESULTS IN 7.8 INCHES.
DOING THE SAME FOR KRST RESULTS IN ABOUT 11 INCHES. LOOKING AT THE
COOK SNOW TECHNIQUE SHOWS 16 DEGREES OF WARM ADVECTION BETWEEN
NORTHERN NM AND CENTRAL WI MIDDAY ON TUESDAY. WHAT IS REALLY 
INTRIGUING IS THAT ALTHOUGH A SOUTHERN STREAM COUPLED JET IS
INDICATED OVER THE OHIO VALLEY TUESDAY NIGHT...THERE IS A NORTHERN
STREAM JET MAX OF 80-100 KNOTS THAT FORMS OVER AND TO THE NORTH OF
LAKE SUPERIOR. THIS PLACES MUCH OF OUR FA IN AN AREA OF MODERATE
TO STRONG DIFFERENTIAL LAYER DIVERGENCE.

SO...NO WINTER STORM WATCH YET...BUT WE ARE GETTING CLOSE IF WE
CAN MAINTAIN ONE MORE CYCLE OF THE CANADIAN...GFS AND ECMWF
SHOWING WHAT COULD BE A PRETTY GOOD WINTER STORM FROM LATE
TUESDAY INTO WEDNESDAY. ITS LOOKING MORE AND MORE LIKE OUR SE HALF
COULD SEE 6 OR MORE INCHES OF SNOW. IN ADDITION...THE PRESSURE
GRADIENT THAT DEVELOPS WOULD INDICATE NEAR 30 MPH SUSTAINED WINDS
TUESDAY NIGHT AND MUCH OF WEDNESDAY ACROSS SOUTH CENTRAL MN AND
ADJACENT AREAS OF WI WITH BLOWING AND DRIFTING SNOW. THE CHANGES
MADE TODAY WERE TO EXPAND THE SNOW CHANCES INTO THE LIKELY TO
CATEGORICAL CATEGORIES OVER JUST ABOUT ALL OF THE CWA FOR TUESDAY
NIGHT AND ACROSS THE EASTERN TWO-THIRDS ON WEDNESDAY.

A CHECK OF THE CIPS WINTER WEATHER ANALOG GUIDANCE TODAY USING THE
72 HOUR FORECAST FROM THE GFS INDICATED JAN 21 1982 AS THE NUMBER
ONE ANALOG. ARCTIC HIGH OVER SOUTH CENTRAL CANADA...DEEP UPPER LOW
OVER THE FAR WEST SHEARING EAST AND AN INVERTED SURFACE TROUGH UP
ACROSS THE FA. THIS ANALOG PRODUCED SOME VERY HEAVY SNOW ACROSS
PARTS OF THE FA.

BEYOND THE MID WEEK STORM...A NEW SURGE OF ARCTIC AIR WILL BE
FLOWING IN WITH MORE BELOW NORMAL TEMPERATURES. IN FACT...THE
FORECAST FOR WEDNESDAY HAS LITTLE TO NO RECOVERY WITH THE HIGH 
TEMPERATURES ACROSS WESTERN AND SOUTHERN MN. THE ARCTIC SLIDE
WILL BE UNDERWAY.

&&

.AVIATION.../06Z TAF ISSUANCE/ 
AREA OF LOW VFR CIGS 030-050 OVER SE MN AND WEST CENTRAL WI IN AN
AREA OF WEAK LIFT WILL LINGER THROUGH ABOUT 09Z-10Z OVER WI NEAR
KEAU AND UNTIL ABOUT 08Z NEAR KMSP. SMALL AREA OF MVFR CIGS SW OF
KRWF GENERALLY DRIFTING TOWARD THE SW AND SHOULD REMAIN TO THE SW
AS WEAK RIDGING TAKES OVER. AN ADDITIONAL AREA OF CONCERN IS A
LARGER AREA OF MVFR CIGS OVER NORTHERN MN WHICH IS DROPPING SW AT
AROUND 10 TO 12 KNOTS SOME OF THIS WILL MOVE INTO THE KAXN AREA
10Z-12Z AND PERSIST THROUGH THE MORNING BUT LIFTING SOME IN THE
AFTERNOON. PRESENT THINKING IS THAT MVFR CIGS COULD AFFECT KRWF
BUT LESSER CHANCES AT KSTC. A LOW PRESSURE AREA TO OUR SOUTH COULD
BRING IN LIGHT SNOW TO THE SOUTH OF THE TAF SITES LATE IN THE
PERIOD LEAVING SCT-BKN 030-050 CLDS UNDER A MID LEVEL CIGS FROM
THE AFTERNOON TO THE END OF THE TAF PERIOD.

&&

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

$$

RAH/JPR