Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 232150
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
350 PM CST TUE DEC 23 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 342 PM CST TUE DEC 23 2014

SFC ANALYSIS PUTS THE SW-NE ELONGATED SFC LOW PRES CENTER OVER
CENTRAL WI...AND THIS SHOWS UP NICELY ON VIS SATELLITE IMAGERY
JUST W OF KGRB. ALOFT...ITS UPPER LEVEL COUNTERPART IS SHIFTED
SLIGHTLY NE OVER THE UP OF MI...AND MODELS SHOW THE LOW ALOFT
SHIFTING AWAY TO THE NE WHILE THE SFC CYCLONE WILL BE MUCH SLOWER
TO MOVE AWAY FROM THE AREA. SO WHILE THE LACK OF UPPER LEVEL
SUPPORT MEANS A GRADUAL DIMINISHING AND EASTWARD SHIFT OF THE
PRECIP ACROSS THE AREA...THE SFC LOW WILL KEEP WIDESPREAD LOW
CLOUDS AND BR/DZ IN PLACE FOR MUCH OF THE PERIOD. THE LACK OF ICE
ALOFT PLUS SOME DRYING OUT OF THE MID-LEVELS WILL ALSO CONTRIBUTE
TO THE VERY LIGHT QPF OF ANY PRECIP THROUGH THIS SHORT-TERM
PERIOD...BUT WILL ALSO CONTRIBUTE TO THE PRODUCTION OF MIST AND
DRIZZLE IN PATCHES ACROSS THE AREA...FOR MAINLY THE EVENING AND
EARLY MORNING HOURS. SOME FOG MAY WELL DEVELOP OVER THE ERN HALF
OF THE CWFA OVERNIGHT INTO TOMORROW WITH SOME WARMER DEWPOINT AIR
ATOP COOLER SFCS...BUT THIS WOULD BE MORE OF A PROBLEM WITH MORE
PREVALENT SNOW COVER...AND THIS IS NOT THE CASE FOR A WIDE MARGIN
OF THE WFO MPX CWFA. SPEAKING OF THE LACK OF SNOW COVER... THIS
WILL AID IN KEEPING TEMPERATURES MORE MILD OVERNIGHT THRU TOMORROW
AS FLOW ALOFT WILL NOT BE CONDUCIVE TO BRINGING IN SIGNIFICANTLY
COLDER AIR FOR TOMORROW ON THE BACKSIDE OF THIS LOW. THE NW FLOW
ALOFT WILL BE MORE APT TO BRING IN SOME COLDER AIR IN WRN
MN...WHERE THERE MAY WELL BE A FEW MORE BREAKS IN THE OVERCAST
PLUS STRONGER NW CAA...BUT BY AND LARGE TEMPERATURES WILL BE
FAIRLY STEADY IN THE UPPER 20S TO MID 30S THRU MIDDAY TOMORROW.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 342 PM CST TUE DEC 23 2014

MAIN STORY DURING THE LONG TERM IS THE EXPECTED CONTINUED
AMPLIFICATION IN THE ERN PAC RIDGE...RESULTING IN INCREASINGLY NW
FLOW...ALONG WITH TEMPERATURES RETURNING BACK TO THE BELOW SIDE OF
NORMAL BY THIS TIME NEXT WEEK. NOT MUCH WEATHER IS EXPECTED OVER THE
NEXT WEEK THOUGH...WITH JUST A LIGHT SNOW EVENT EXPECTED ON
FRIDAY...WITH ANOTHER POSSIBLE DUSTING IN THE SUN/MON TIMEFRAME.

THE LONG TERM WILL START ON CHRISTMAS DAY WITH A SHORTWAVE RIDGE
MOVING THROUGH...ALONG WITH ANOTHER WARM BUBBLE OF AIR AT H85 THAT
WILL SEE TEMPS AT THAT LEVEL RISE ABOVE 0C. WE WILL HAVE A COLD
FRONT STALLING OUT ACROSS WRN/CENTRAL MN AS WELL...WITH HIGHS AHEAD
OF THE FRONT GETTING INTO THE 35-40 RANGE. NORTH OF THIS WARM
NOSE/FRONT...THERE WILL BE ENOUGH ISENTROPIC LIFT TO GET A BAND OF
PRECIP GOING...BUT ANY PRECIP...IF IT FALLS...WOULD BE ACROSS
CENTRAL MN.

THURSDAY NIGHT AND FRIDAY...WE WILL SEE AN ELONGATED POSITIVELY
TILTED H5 THROUGH WORK ACROSS THE AREA...MODELS CONTINUE TO SHOW A
QUICK HIT OF SNOW WORKING ACROSS THE AREA IN RESPONSE TO ISENTROPIC
LIFT ON THE 290-300K SFC AND FGEN IN THE H7-H6 LAYER. ALL GUIDANCE
SHOW A SW-NE ORIENTED BAND OF 1-3 INCHES OF SNOW FALLING ACROSS MN.
THE NAM IS ON THE NORTH END OF THE ENVELOPE WITH THE BAND FALLING
FROM FARGO INTO THE ARROWHEAD...WHILE THE GEM SETS THE SOUTH END
WITH THE SNOW FALLING FROM NEW ULM THROUGH THE TWIN CITIES TO
HAYWARD. FOLLOWED THE ECMWF/HPC PROGS...WHICH SPLITS THE DIFFERENCE
WITH THIS BAND FALLING FROM ROUGHLY MADISON TO DULUTH. SOUTH OF THIS
BAND THERE WILL BE A DRY SLOT...WITH VERY DRY AIR COMING UP AT
H7...SO WE SHOULD SEE A PRETTY SHARP CUT OFF IN THE SNOWFALL TO THE
SOUTH.

NEXT POTENTIAL SNOW MAKER LOOKS TO COME IN THE SUN/MON TIMEFRAME AS
A CLIPPER COMES DOWN WITH A SURGE OF ARCTIC AIR. AGAIN...THIS DOES
NOT LOOK TO REALLY BE MUCH OF AN ISSUE OR SNOW MAKER FOR THAT
MATTER. IN FACT...FOR THE REST OF DECEMBER...THE SYSTEM FRIDAY
LOOKS TO BE ABOUT OUR LAST SHOT AT SNOWFALL FOR THE MONTH. WITH BOTH
STC AND MSP SITTING AROUND 1.5" OF SNOW ON THE MONTH...THERE IS A
GOOD CHANCE THAT THIS COULD BE THE FIRST TIME SINCE 2004 THAT BOTH
LOCATIONS FAILED TO GET MORE THAN 2" OF SNOW FOR THE MONTH OF
DECEMBER.

FOR TEMPERATURES...BOTH THE GFS AND ECMWF AGREE THAT BY NEXT
TUESDAY WE WILL BE BACK IN ARCTIC AIR...BUT THEY DISAGREE
CONSIDERABLY ON WHEN WE GET THERE. THE GFS HAS TEMPERATURES
REMAINING MORE OR LESS STEADY THROUGH FRIDAY...BEFORE STARTING TO
DROP OFF FRIDAY NIGHT AS CAA KICKS IN. THE ECMWF DROPS TEMPS
SLIGHTLY THIS WEEKEND...BUT DOES NOT REALLY BRING IN THE STRONG CAA
UNTIL SUNDAY NIGHT. THE RESULT IS THAT THE ECMWF IS A GOOD 10-15
DEGREES WARMER THAN THE GFS THIS WEEKEND. THIS FAR OUT...STAYED WITH
A BLENDED FORECAST...THOUGH BASED ON HOW MUCH THE COLD AIR HAS
STRUGGLED TO GET INGESTED INTO THE SYSTEM OFF TO OUR EAST
TODAY...WOULD FAVOR THE WARMER SOLUTION FOR THE WEEKEND. BY NEW
YEARS EVE...BOTH THE GFS/ECMWF HAVE 925-850 TEMPS THAT WOULD SUPPORT
LOWS LESS THAN -20 WITH HIGHS BELOW ZERO IF WE HAD OUR TYPICAL 6-10
INCHES OF SNOW ON THE GROUND. HOWEVER...WITH MOST PLACES 6-10 INCHES
BELOW NORMAL ON SNOW COVER...THIS COLD SURGE AROUND NEW YEARS WILL
BE SIGNIFICANTLY MODIFIED BY THE BARE GROUND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1159 AM CST TUE DEC 23 2014

PERSISTENT DEGRADED CONDITIONS TO LAST THROUGH MUCH OF TOMORROW AS
A LARGE LOW PRESSURE SYSTEM LUMBERS EASTWARD THROUGH THE REGION.
CEILINGS ARE STRADDLING THE MVFR/IFR THRESHOLD AT INITIALIZATION
TIME...AND ARE EXPECTED TO DROP INTO IFR RANGE FOR ALL SITES THIS
EVENING THRU TOMORROW MORNING. THE TRICKY PART WILL BE DETERMINING
VISIBILITY DUE TO THE PATCHY/BANDED NATURE OF ONGOING
PRECIPITATION. THE PRECIP AS A WHOLE WILL STEADILY WEAKEN...BUT
THERE IS A CHANCE THAT SOME MOD/HVY PATCHES OF THE PRECIP MAY HIT
ONE OF THE MPX TERMINALS...SPECIFICALLY RNH-MSP. NOT LOOKING FOR
ANYTHING LONG-DURATION...BUT ENOUGH TO DROP VSBY INTO IFR RANGE.
OTHERWISE...PREVAILING VSBY AT ALL SITES WILL BE MVFR AS THE
PRECIP WILL BE VERY LIGHT /-SHSN/. WINDS WILL SLOWLY BACK FROM NNE
TO NW OVERNIGHT THRU TMRW MRNG.

KMSP...MSP STARTS OUT WITH MVFR CEILINGS BUT MAY DROP EASILY INTO
UPPER-END IFR AT ANY POINT THIS AFTN INTO THIS EVE SO THAT WILL
NEED TO BE MONITORED. ASIDE FROM THE POTENTIAL FOR A MOD-HVY BAND
OF -SN IN THE FIRST COUPLE HRS OF THE 18Z TAF...PRECIP INTENSITY
WILL BY AND LARGE BE LIGHT...BUT SO LIGHT THAT IT MAY RESULT IN
MIST THAT WOULD REDUCE VSBY. ATTM...AM THINKING ONLY MVFR VSBY
CATEGORY IN THAT CASE. CONDS TO REMAIN DEGRADED THRU THE DAY
TMRW...INCLUDING A STRONG LIKELIHOOD OF IFR CEILINGS OVERNIGHT
INTO TMRW AFTN.

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


&&

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

$$

SHORT TERM...JPC
LONG TERM...MPG
AVIATION...JPC






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