Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 151854
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1254 PM CST MON DEC 15 2014

.UPDATE...FOR 18Z AVIATION DISCUSSION BELOW

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 341 AM CST MON DEC 15 2014

WELL THE WINTER WEATHER EVENT WE`VE BEEN TALKING ABOUT FOR 5 DAYS
NOW IS FINALLY HERE. THE PRECIP SHIELD IS NEARING THE SOUTHERN
MINNESOTA BORDER AND WILL CONTINUE ITS STEADY MOVEMENT NORTHWARD
TODAY. WE MAINTAINED THE WINTER WEATHER ADVISORY AND WARNING AS
IS...WITH NO CHANGE IN LOCATION OR TIMING. EVEN THOUGH MOST OF THE
LIQUID WILL FALL OVER THE NEXT 12-18 HOURS...THE AMOUNT OF ICING IN
WEST CENTRAL AND SOUTH CENTRAL MINNESOTA TODAY IS STILL SOMEWHAT
UNCERTAIN...HOWEVER...GIVEN THE RELATIVELY WARM SURFACE TEMPS...WE
DON`T THINK ICE ACCUMULATION WILL GET OUT OF HAND TODAY. IN
FACT...THE CHANGE OVER FROM RAIN TO SLEET AND SNOW MAY HAPPEN
RELATIVELY QUICKLY ONCE IT BEGINS...LEAVING A SMALL WINDOW FOR THE
ALWAYS DANGEROUS FREEZING RAIN.

THE SURFACE TROUGH/COLD FRONT HAS ADVANCED INTO EASTERN MINNESOTA
AND HAS SET UP QUITE THE TEMPERATURE GRADIENT ACROSS MINNESOTA WITH
50S IN THE FAR EAST AND LOWER TO MID 30S IN THE FAR WEST. AS
MENTIONED ABOVE...WIDESPREAD PRECIP IS MAKING PROGRESS TO THE NORTH
OUT AHEAD OF A VERY NICE WATER VAPOR SIGNATURE IN THE SOUTHERN AND
CENTRAL PLAINS THIS MORNING. WE EXPECT WIDESPREAD PRECIP TODAY.
SO...100% POPS ARE IN THE FORECAST...AND OUTSIDE OF COUNTIES SUCH AS
STEVENS AND DOUGLAS...GETTING LIQUID TO REACH THE GROUND WILL
CERTAINLY NOT BE A PROBLEM TODAY. IN FACT...WE`RE EXPECTING
WIDESPREAD 0.25"-0.75" LIQUID EQUIVALENT TODAY ACROSS MUCH OF THE
FORECAST AREA.

THE QUESTION ALL ALONG IS HOW FAST WILL THE TEMPERATURES AT THE
SURFACE DROP BELOW FREEZING RELATIVE TO THE HOW FAST WE GET RIDE OF
THE WARM LAYER ALOFT. THE FORECAST SOUNDINGS /GFS-NAM-RAP/ AT
LOCATIONS SUCH AS KRWF MAINTAIN THE WARM LAYER AT 800-850MB UNTIL
THE MID TO LATE AFTERNOON...BUT ALSO MAINTAIN SURFACE TEMPERATURE
NEAR OR JUST ABOVE FREEZING. IF THIS IS THE CASE...MUCH OF THE
ADVISORY/WARNING AREAS COULD LOSE A LOT OF QPF TO JUST PLAIN OLD
COLD RAIN /WET ROADS AND 33-34 DEGREES/. THE AIR IS COLDER BACK
ACROSS FAR WEST CENTRAL MN...BUT THESE AREAS SHOULD BE ON THE FRINGE
OF THE EXPECTED PRECIP SHIELD TODAY. OVERALL...THE DATA THIS MORNING
SUGGESTS WHEN THE SURFACE TEMPS DROP TO 31-32 DEGREES...THE PROFILE
WILL COOL ENOUGH TO GET SLEET OR SNOW. THIS IS GOOD NEWS...BECAUSE
IT SHOULD LIMIT THE AMOUNT OF ICING DUE TO FREEZING RAIN.
NOW...THERE IS A CAVEAT...POWERLINES AND TREES CAN BE A DEGREE OR
TWO COOLER THAN THE SURFACE AND ACCUMULATE EVEN IF ROADS/SIDEWALKS
DO NOT. FOR GOOD ICING...HOWEVER...WE REALLY NEED TO SEE SURFACE
TEMPS CLOSER TO 30 OR COLDER...THAT WAY THE LATENT HEAT RELEASE DUE
TO FREEZING DOESN`T WARM THE NEAR SURFACE AIR. THE WARNING COULD
STILL PAN OUT...IT WILL BE CLOSE...BUT WE WILL CERTAINTY NOT BE
SURPRISED IF THE IMPACTS DUE TO ICING /OR LACK THERE OF/ ARE LIMITED
BY TEMPS THE HANG RIGHT AT 32-34 DEGREES WHILE THE MODERATE TO HEAVY
PRECIP IS FALLING. NOTHING TOO DIFFERENT LATE THIS EVENING WITH THE
P-TYPE GOING OVER TO SNOW WITH 1-4" INCHES ACROSS A LARGE CHUNK OF
MINNESOTA BY TUESDAY MORNING.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 341 AM CST MON DEC 15 2014

PICKING UP THE FORECAST TUESDAY MORNING...THE ONGOING SYSTEM FOR
TODAY WILL HAVE ITS PRECIPITATION EAST OF ALMOST THE ENTIRE FA BY
6AM TOMORROW MORNING. BY THIS TIME...THE SURFACE LOW WILL BE NEAR
DETROIT...WITH RAPID DRYING OCCURRING IN THE MID LEVELS OF THE
ATMOSPHERE BEHIND THE SYSTEM. SO...SMALL POPS FOR WESTERN WI
REMAIN IN THE FORECAST FOR TUESDAY MORNING AS THE PRECIP EXITS TO
THE EAST.

SKY COVER WILL SLOWLY DECREASE TUESDAY. THE NAM IS STILL
INDICATING VERY HIGH RH JUST ABOVE THE GROUND...BUT THE EC AND GFS
INDICATE AT LEAST SOME DRYING AT THIS LEVEL. THE PROBLEM IS...A
NORTHERN STREAM SHORTWAVE WILL BE STRENGTHENING THROUGH THE
DAY...KEEPING US UNDER CYCLONICALLY CURVED FLOW. THIS WAVE LOOKS
DRY...WITH NOTHING MORE THAN FLURRIES OR VERY LIGHT SNOW SHOWERS
EXPECTED. THE CYCLONICALLY CURVED FLOW COULD ALLOW SOME CLOUDS TO
LINGER IF THE NAM IS ON TO SOMETHING WITH THE ADDED MOISTURE.
SOUTHWESTERN MN HAS THE BEST CHANCE OF BREAKING OUT IN TO
SUNSHINE.

WEDNESDAY AND THURSDAY...A SURFACE HIGH WILL BUILD IN TO THE
REGION BEHIND THIS NORTHERN WAVE...WITH MUCH MORE SEASONAL
TEMPERATURES FOR HIGHS AND LOWS BEGINNING TOMORROW. THE NEXT
SYSTEM TO WATCH IS A DEEP TROUGH CURRENTLY OUT IN THE PACIFIC
OCEAN THAT WILL PUSH ASHORE TOMORROW AND PROGRESS EASTWARD THROUGH
THE WEEK. THE EC/GFS DIFFER QUITE A BIT IN THE STRENGTHENING OF
THIS SYSTEM...WHICH ALSO IMPACTS THE POSITIONING OF IT THROUGH THE
WEEK. THE EC TAKES THE POSITIVELY TILTED UPPER TROUGH AND PIVOTS
IT TO MORE OF A NEGATIVE TILT AS A SURFACE CYCLOGENESIS OCCURS IN
THE DEEP SOUTH. WITH THE STRONGER SOLUTION...THE EC TAKES THE LOW
ACROSS THE DEEP SOUTH WITH THE NORTHERN EXTENT OF THE PRECIP
SHIELD REACHING AS FAR NORTH AS THE OHIO RIVER VALLEY. SO A DRY
FORECAST FOR THE LOCAL AREA AS WE REMAIN UNDER THE INFLUENCE OF
SURFACE HIGH PRESSURE. THE GFS HAS THE SYSTEM WEAKER AND ABOUT ONE
STATE NORTH...BUT STILL KEEPS THE PRECIP SOUTH OF OUR FORECAST
AREA. SEASONAL TEMPERATURES LOOK TO CONTINUE THROUGH THE END OF
THE LONG RANGE FORECAST PERIOD.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1255 PM CST MON DEC 15 2014

WIDESPREAD IFR AND LIFR CONDITIONS WILL PREVAIL INTO THIS EVENING.
RAIN AND MIXED PRECIPITATION WILL TRANSITION TO SNOW AT WESTERN
SITES /KAXN AND KRWF/ THIS AFTERNOON...AND AT CENTRAL/EASTERN
SITES /KMSP-KRNH-KEAU/ THIS EVENING. LIGHT TO MODERATE SNOW THEN
LINGERS TONIGHT...WITH PREVALENT MVFR CONDITIONS THROUGH TUESDAY
MORNING. STRONG NORTH-NORTHWEST WINDS THROUGH THE PERIOD...WITH
SUSTAINED 15-20KT SPEEDS AND GUSTS TO BETWEEN 25 AND 35 KTS.

KMSP...
VSBYS SHOULD HOVER IN THE 1-2SM RANGE WITH CIGS BELOW 500 FT
THROUGH THIS AFTERNOON. THE PRECIP TYPE SHOULD BE RAIN THROUGH THE EVENING
COMMUTE...WITH A 1-2 HOUR MIX OF RAIN/SLEET AROUND 1Z. THE
TRANSITION TO SNOW IS EXPECTED AROUND 3Z...WITH MVFR CONDITIONS
AND -SN THROUGH THE OVERNIGHT HOURS. THE PRECIP SHUTS OFF FOR
TUESDAY...BUT CIGS REMAIN MVFR THROUGH MOST OF THE PERIOD.

/OUTLOOK FOR KMSP/

WED...VFR. WINDS NW 10 KTS.
THU...VFR. WINDS W 5 KTS.
FRI...VFR. WINDS SSE 5 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR
     MNZ041>043-047>049-054-055-058.

     WINTER WEATHER ADVISORY UNTIL 3 AM CST TUESDAY FOR MNZ044-045-
     050>052-059-066>068-075.

     WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR MNZ056-057-
     064-065-073.

     WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR MNZ074-
     082.

WI...DENSE FOG ADVISORY UNTIL 6 PM CST THIS EVENING FOR WIZ014>016-
     023-025-027-028.

&&

$$


SHORT TERM...CLF
LONG TERM...SPD
AVIATION...LS





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