Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 230058 AAA
AFDMPX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
658 PM CST MON DEC 22 2014

.UPDATE...
ISSUED AT 650 PM CST MON DEC 22 2014

THE CHANGE OVER TO SNOW IS OBVIOUSLY TAKING ITS TIME THIS EVENING.
THERE SEEM TO BE A FEW REASONS WHY. OUR BALLOON LAUNCHED A COUPLE
HOURS AGO SHOWED A FREEZING LEVEL AT ABOUT 1000FT ABOVE THE
GROUND. THAT`S TYPICALLY THE ROUGH THRESHOLD FOR A RAIN-TO-SNOW
CHANGE. SURFACE TEMPS ARE GENERALLY IN THE MID 30S...WHICH WOULD
CERTAINLY YIELD SNOW IF WE HAD SATURATION OVER A DEEP LAYER (AND
THROUGH THE DENDRITE GROWTH ZONE). AS OF RIGHT NOW...WE ARE
SOMEWHAT LACKING SATURATION IN THAT LAYER...WHICH IS ABOVE
10-12KFT. WE ARE ALSO LACKING IN FORCING. WE HAVE WEAK OMEGA WITH
THE APPROACHING TROUGH. IF THE LIFT WERE STRONGER WE WOULD
UNDOUBTEDLY HAVE DEEPER SATURATION AND IT WOULD BE SNOWING ALMOST
EVERYWHERE. SO...RIGHT NOW...WE ARE KIND OF WAITING FOR THE FLOW
TO BECOME MORE E-NE SO WE GET SOME COLD ADVECTION - ALONG WITH
SOME MINOR COOLING DUE TO NIGHTFALL. VARIOUS LOCATIONS AROUND THE
FORECAST AREA THAT HAVE A LITTLE HIGHER ELEVATION HAVE BEEN
REPORTING LIGHT SNOW OR "UP" AT TIMES THIS EVENING. THE MAIN
PRECIP BAND ARRIVES BY ABOUT MID MORNING AND MOST OF THAT WILL BE
SNOW GIVEN THE GOOD FORCING. THAT WILL BE FAIRLY FAR TO THE
EAST...IN FAR EASTERN MN AND WESTERN WI. SO WITH THAT...WESTERN
AND EVEN MUCH OF CENTRAL MN COULD BE ON THE OUTSIDE OF THE MAIN
SNOW BAND AND THUS RECEIVE LITTLE SNOW. THIS INCLUDES PLACES LIKE
ST. CLOUD, LITCHFIELD AND REDWOOD FALLS. THE TC METRO STILL LOOKS
OK FOR MINOR SNOW ACCUMS...BUT THE BEST LOCATIONS SHOULD BE FROM
ALBERT LEA TO EAU CLAIRE.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 322 PM CST MON DEC 22 2014

LIGHT SNOW IS BEGINNING TO MIX IN WITH THE RAIN AT MID AFTERNOON
ACROSS THE TWIN CITIES AND POINTS SOUTH TO IOWA AS THE THERMAL
PROFILE IS BEGINNING TO COOL BELOW 0C IN THE 875-925MB LAYER. EVEN
SURFACE TEMPERATURES HAVE COOLED A COUPLE OF DEGREES THIS
AFTERNOON ACROSS MUCH OF OUR FA. CONTINUED COOLING HEADING INTO THE
EVENING HOURS WILL LIKELY LEAD TO MUCH OF THE PRECIPITATION ACROSS
CENTRAL MN THROUGH THE TWIN CITIES AND WEST CENTRAL WI BECOMING
SNOW. SHORT TERM MODEL SOLUTIONS INDICATE A DIMINISHING TREND TO
THE PRECIPITATION IN THESE AREAS WHICH SHOULD KEEP SNOW
ACCUMULATIONS MINIMAL. IT REMAINS WARMER OVER WEST CENTRAL THROUGH
SOUTH CENTRAL MN THIS EVENING WITH JUST LIGHT RAIN EXPECTED.
HOWEVER...VISIBILITIES HAVE LOWERED NEAR THE BUFFALO RIDGE...ALONG
THE SURFACE TROUGH AXIS...AND SOME DENSE FOG CAN BE EXPECTED EARLY
TONIGHT SOUTHWEST OF THE MN RIVER VALLEY UNTIL WINDS BECOME MORE
NORTHEAST LATER TONIGHT.

TUESDAY REMAINS A REAL PROBLEM WEATHER WISE. A CLOSED MID LEVEL
LOW WILL EJECT NORTHEAST FROM IA INTO WI DURING THE DAY. THIS
PLACES A DEFORMATION ZONE FROM SOUTH CENTRAL MN THROUGH WEST
CENTRAL WI. THE THERMAL PROFILE INDICATES THIS WILL BE MAINLY AN ALL
SNOW EVENT. HOWEVER...SOME WARMER AIR ARRIVES INTO WEST CENTRAL WI
DURING THE MORNING IN THE 850-900MB LAYER WITH TEMPERATURES RISING
ABOVE 0C ALLOWING FOR A MIX OF RAIN AND SNOW. MODEL SPREAD REMAINED
TODAY WITH TIMING AND DEPTH WITH THIS SYSTEM BUT MORE IMPORTANTLY
WITH THE EXPECTED PRECIPITATION AMOUNTS. FOR THIS REASON THE SREF
WAS USED FOR QPF AMOUNTS AS IT WAS HIGHER THAN MOST SOLUTIONS.
THIS PLACED BETWEEN 0.15 AND 0.25 INCHES OF QPF IN THE
AFOREMENTIONED AREAS. THE PROBLEM THAT ARISES IS WITH THE SNOW
RATIOS. THE AF SNOW RATIO METHOD RESULTS IN VALUES IN THE RANGE OF
3:1 TO 5:1. THE COBB TECHNIQUE WOULD BE MORE IN THE 8:1 TO 9:1
RANGE. THE COBB VALUES WERE USED BUT WITH RATIOS LESS THAN 10:1
SNOW AMOUNTS ONLY CAME UP IN THE 1 TO 2 INCHES RANGE IN THE
MORNING WITH ANOTHER HALF INCH TO 1 INCH IN THE AFTERNOON. STILL
THINK THESE MAY BE TOO LOW WITH A POTENTIAL 4 INCH BAND POSSIBLE
BEGINNING SOMEWHERE BETWEEN FAIRMONT AND ALBERT LEA AND EXTENDING
NORTHEAST THROUGH DAKOTA COUNTY AND THEN THROUGH NEW RICHMOND AND
RICE LAKE IN WEST CENTRAL WI. AREAS TO THE WEST AND NORTH WILL SEE
MUCH LESS SNOW. ALL OFFICES HELD ON TO THE WINTER WEATHER ADVISORY
FOR PORTIONS OF WI DUE TO THE UNCERTAINTY OVERNIGHT AS WELL AS ON
TUESDAY. LITTLE VARIATION IN THE TEMPERATURES TONIGHT AND TUESDAY
WITH LOWS TONIGHT IN THE 31-34 DEGREE RANGE WITH HIGHS ON TUESDAY
FROM 33 TO 36.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 322 PM CST MON DEC 22 2014

TWO CONCERNS OVER THE NEXT SEVERAL DAYS...ONE FOR TUESDAY
EVENING...WITH ANOTHER PROBLEM BY THE END OF THE WEEK.

THE TRANSITION FROM TUESDAY INTO TUESDAY NIGHT WILL BE ASSOCIATED
WITH THE DECAYING UPPER LOW ACROSS THE WESTERN GREAT LAKES...WITH A
STRONGER UPPER LOW/SFC LOW/ DEVELOPING ON THE SOUTHERN JET ACROSS
MO/AR/IL. CONFIDENCE REMAINS HIGH ENOUGH TO CONTINUE HIGH END CHC
POPS FOR TUESDAY EVENING ACROSS MOST OF THE CWA. THE MAIN REASON IS
THE DEFORMATION ZONE CENTERED ACROSS OUR REGION...WILL CONTINUE TO
SHEAR OUT...SQUEEZING OUT A FEW HUNDREDTHS...RESULTING WITH AN
ADDITIONAL HALF INCH OF SNOW. AGAIN...NOT EXPECTING TOO MUCH
ESPECIALLY CONSIDERING THE SOUTHERN STREAM HAVING MORE INFLUENCE ON
THE OVERALL WEATHER PATTERN.

ALTHOUGH THE PATTERN REMAINS PROGRESSIVE ACROSS THE CONUS THIS
WEEK...THE RESULTING SLOWER MOVEMENT OF TODAY/S TUESDAY SYSTEM WILL
LEAD TO A SLOWER SOLUTION FOR THE SYSTEM BY THE END OF THE WEEK. THE
EC AND THE LOCAL HOPWRF /24KM/ SOLUTIONS HAVE SHOWN FRIDAY SYSTEM
WARMER AND FURTHER NORTHWARD ACROSS THE UPPER MIDWEST. IN
ADDITION...THERE WILL LIKELY BE A STRONG THERMAL GRADIENT ALONG WITH
A SHARP CONTRAST BETWEEN THE DRIER AIR TO THE SOUTH...AND THE
STRONGER FRONTAL BANDING TO THE NORTH. BASICALLY...IT IS QUITE
POSSIBLE WE CAN SEE A LOCALIZED BAND OF 6+ INCHES OF SNOW WHERE THE
STRONGEST BANDING OF THE 85H/70H/60H FRONT LIES FRIDAY/FRIDAY NIGHT.
THE BEST SCENARIO IS TO CONTINUE CHC POPS...LEAN MORE TOWARD HIGHER
QPF AMTS ACROSS OUR NW CWA AS THIS SYSTEM EVOLVES THRU THE NEXT FEW
DAYS.

TEMPS WILL LIKELY REMAIN ABV NORMAL THRU AT LEAST FRIDAY...OR UNTIL
FRIDAY/S SYSTEM BRINGS DOWN COLDER AIR FOR THE END OF THE YEAR.
LONGER RANGE MODELS HAVE DEPICTED THE COOLER TEMPS FOR THE FIRST
WEEK OF 2015...BUT NOTHING TOO ABNORMAL...MAINLY CLIMATOLOGY
WHICH IS LOWS AROUND 5 TO 10...WITH HIGHS IN THE TEENS AND 20S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 602 PM CST MON DEC 22 2014

WE SOUND A LITTLE LIKE A BROKEN RECORD HERE...BUT GENERALLY IFR
CONDITIONS ARE EXPECTED THROUGH THE NIGHT AND INTO TOMORROW. THERE
HAS BEEN SOME IMPROVEMENT WITH CIGS AND VISBY GOING TO MVFR IN
WESTERN WI AND FAR EASTERN MN...THIS COULD EASILY LINGER FOR MOST
OF THE EVENING BUT EVENTUALLY WE DO EXPECT IFR TO RETURN TONIGHT -
ESPECIALLY WHEN THE -RA/-DZ CHANGES OVER TO -SN. EVEN LIGHT SNOW
DOES A GOOD JOB OF REDUCING VIS. SPEAKING OF SNOW...WE EXPECT
LITTLE IMPACTS DUE TO SNOW ACCUMULATING ON RUNWAYS TONIGHT. WITH
TEMPS NEAR OR JUST ABOVE FREEZING THE GROUND IS WET AND RELATIVELY
WARM. WE WOULD NEED BETTER SNOW RATES THAN WHAT IS EXPECTED
TONIGHT TO ACCUMULATE ON THESE SURFACES. MOST LIKELY WE ARE JUST
LOOKING AT A DUSTING ON GRASS OR ELEVATED SURFACES TONIGHT OR
NOTHING AT ALL. THE BETTER SNOW RATES MOVE IN SHORTLY AFTER
SUNRISE TOMORROW. KSTC/KAXN AND EVEN KRWF MIGHT BE SHOULD BE JUST
ON THE OUTSIDE OF THE BETTER ACCUMULATING SNOW TOMORROW.

KMSP...

WE`LL LIKELY HANG ONTO VFR CEILINGS FOR AT LEAST A COUPLE MORE
HOURS AND THEN SEE THE CEILINGS GET BACK DOWN BELOW 1000FT AND
ALSO A VIS REDUCTION TONIGHT. WE DON`T EXPECT MUCH SNOW
TONIGHT...AND AS MENTIONED ABOVE...GIVEN THE SURFACE TEMPS AND
LIGHT NATURE OF THE SNOW TONIGHT...ACCUMULATION ON RUNWAYS WILL BE
LITTLE TO NONE. WE`LL HAVE TO WATCH OUT FOR THE SECOND HALF OF THE
MORNING COMMUTE TOMORROW...THE HEAVIER SNOWBAND WILL BE
APPROACHING BY THEN. ALTHOUGH...MOST OF THE ACCUMULATING SNOW WILL
OCCUR AFTER 14Z-15Z.

/OUTLOOK FOR KMSP/
WED...MVFR. WINDS NW 10-15 KTS.
THU...VFR. WINDS W 5-10 KTS.
FRI...MVFR CHC -SN. WINDS NW 10 KTS.


&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM CST
     TUESDAY FOR WIZ016-027.

&&

$$

UPDATE...CLF
SHORT TERM...RAH
LONG TERM...JLT
AVIATION...CLF








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