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000
FXUS65 KBYZ 091031
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
331 AM MST MON DEC 9 2013

.SHORT TERM...VALID FOR TDY AND TUE...

WIND-RELATED WINTER WEATHER ISSUES TODAY WILL TRANSITION BACK TO A
HIGH PROBABILITY OF 1 TO 2 INCHES OF SNOW IN MANY AREAS TUE AS TWO
SHORT WAVES CROSS THE REGION IN STRONG NORTHWEST FLOW ALOFT. WE DO
STILL EXPECT A SLOW MODERATION IN TEMPERATURES TO CONTINUE THOUGH.

TODAY...LEE-SIDE SURFACE PRESSURE FALLS ON THE ORDER OF 5 HPA/3 HR
CENTERED ACROSS THE CENTRAL ALBERTA-SASKATCHEWAN BORDER EARLY THIS
MORNING WILL REACH NORTHEAST MT AND WESTERN ND BY MIDDAY. THE WIND
SPEEDS IN SOUTH CENTRAL MT WILL CONTINUE RAMPING UP AS THAT OCCURS
AND WILL BE BOOSTED FURTHER BY EXTRA PRESSURE GRADIENT THANKS TO A
FORMIDABLE COLD AIR MASS TRAPPED WEST OF THE LOCAL MOUNTAINS. WIND
SPEEDS IN THE GRIDDED FORECAST WERE HEAVILY WEIGHTED TO RAP OUTPUT
SINCE IT IS HANDLING EARLY-DAY WINDS NEAR BIG TIMBER /WHICH IS THE
FAVORED SPOT FOR THE HIGHEST SPEEDS IN THIS PATTERN/ WELL. WE THUS
HAVE HIGH CONFIDENCE IN SUSTAINED SPEEDS OF 40 TO 50 MPH AND GUSTS
TO 70 MPH FROM LIVINGSTON TO BIG TIMBER TODAY...AND GUSTS UP TO 55
MPH AT HARLOWTON AND 45 MPH AROUND BILLINGS TOO. THE WINDS WILL BE
ON THE INCREASE ON THE PLAINS OF SOUTH CENTRAL AND SOUTHEAST MT BY
21 UTC AS WELL AS MIXING INCREASES AND A MODEST BATCH OF LOW-LEVEL
HEIGHT RISES BEGINS AFFECTING THAT AREA...THOUGH MOMENTUM TRANSFER
WILL BE LACKING AND ONLY SUPPORTS GUSTS TO ABOUT 35 MPH ACROSS THE
SOUTHEAST PART OF MT. ADD IN SNOW SHOWERS WHICH COULD DROP A QUICK
INCH OF SNOW AND REDUCE VISIBILITY ON THEIR OWN TOO OVER SOUTHEAST
MT THOUGH...AND CONDITIONS COULD BE QUITE HAZARDOUS OVER THAT AREA
AS WELL. WE ACTUALLY PUSHED POPS FOR SNOW SHOWER ACTIVITY INTO THE
70-90 PERCENT RANGE OVER SOUTHEAST MT THIS AFTERNOON BASED ON GOOD
AGREEMENT IN 00 UTC GUIDANCE IN NOTABLE QG-FORCING OVER THAT AREA.
NEEDLESS TO SAY...BLOWING AND DRIFTING SNOW IS MENTIONED TODAY AND
INTO THIS EVENING FOR MOST OF THE AREA...THOUGH DEPTH AND PHYSICAL
CHARACTERISTICS OF THE SNOW SUGGEST THE BIGGEST ISSUE COULD END UP
BEING SIGNIFICANT DRIFTING. WE WILL NONETHELESS NEED TO BE WARY OF
THE POSSIBILITY OF BONAFIDE GROUND BLIZZARD CONDITIONS IN THE OPEN
COUNTRY WHERE LOCALLY DEEPER SNOW PACK RESIDES...THOUGH THE CHANCE
OF THAT APPEARS RELATIVELY LOW /SUBJECTIVELY NEAR 30 PERCENT/.

WHERE HEADLINES ARE CONCERNED...WE ADDED ALL OF BIG HORN COUNTY TO
A WINTER WEATHER ADVISORY FROM 18 TO 06 UTC SINCE OUR RAP-WEIGHTED
WIND FORECAST SUPPORTED SPEEDS SUFFICIENT FOR BLOWING AND DRIFTING
SNOW ISSUES THERE TOO. THE REST OF OUR PREVIOUSLY-ISSUED HEADLINES
WERE LEFT IN TACT. WE WILL PROBABLY HIT HIGH WIND CRITERIA FOR THE
SUSTAINED 50 MPH SPEEDS AT BIG TIMBER TODAY...BUT FELT IT WAS BEST
TO COVER THIS WITH ONE PRODUCT...THE WINTER WEATHER ADVISORY. NOTE
THAT IF WINDS IN SOUTH CENTRAL MT /NAMELY IN THE LIVINGSTON TO BIG
TIMBER CORRIDOR/ STAY UP PAST 12 UTC TUE MORNING AS SOME OF THE 00
UTC GUIDANCE SHOWS...PARTS OF THE ADVISORY MAY NEED TO BE EXTENDED
IN TIME WITH A LATER FORECAST RELEASE.

TONIGHT...THE SHORT WAVE WILL EXIT THE AREA...AND WINDS WILL BE ON
A DOWNWARD TREND /ESPECIALLY AFTER 06 UTC/...EVEN THOUGH THEY WILL
STAY GUSTY IN SOUTH CENTRAL MT. WE CAUTIOUSLY FOLLOWED THE LEAD OF
RECENTLY WELL-PERFORMING GUIDANCE THAT SHOWS LOWS ONLY AROUND 10 F
/MUCH WARMER THAN RECENT NIGHTS/ GIVEN EXPECTED LOW-LEVEL MIXING.

TUE...A LIGHT SNOW EVENT IS EXPECTED IN MANY AREAS AS A GOOD BATCH
OF QG-FORCING WITH ANOTHER SHORT WAVE TROUGH RIDES SOUTHEAST ALONG
THE THERMAL BOUNDARY LEFT BEHIND TODAY/S WAVE. IT LOOKS LIKE WINDS
WILL EVEN TURN NORTH OR NORTHEAST IN BILLINGS BY AFTERNOON...SO WE
WILL PROBABLY GET IN ON SOME LIGHT SNOW HERE TOO. WE HAD ENOUGH IN
THE WAY OF CONFIDENCE IN THIS WHOLE SCENARIO TO SIGNIFICANTLY RAMP
UP POPS IN MANY AREAS...GOING AS FAR AS 80 PERCENT FROM MILES CITY
TO HYSHAM AND DOWN TOWARD LAME DEER AND LODGE GRASS. THIS LOOKS TO
BE A GOOD 1 TO 2 INCH SNOW EVENT IN MANY AREAS. SCHULTZ

.LONG TERM...VALID FOR WED...THU...FRI...SAT...SUN...

NORTHWEST FLOW ALOFT ON WEDNESDAY SLOWLY BECOMES A MORE WESTERLY
FLOW ON THURSDAY WHICH WILL ALLOW A LEESIDE SURFACE PRESSURE
TROUGH TO BE THE DOMINANT FEATURE EAST OF THE CONTINENTAL DIVIDE.
THIS PATTERN HOLDS UNTIL LATER ON FRIDAY WHEN AN UPPER LEVEL RIDGE
BUILDING INTO THE PACIFIC NORTHWEST TURNS THE FLOW NORTHWESTERLY
OVER MONTANA AND WYOMING. AT SOME POINT COLDER AIR OVER THE
DAKOTAS WILL HAVE A CHANCE TO PUSH A BACKDOOR COLD FRONT INTO
SOUTHERN MONTANA BUT WHEN IS NOT EXACTLY SURE...WHETHER IT WILL BE
FRIDAY NIGHT OR SATURDAY NIGHT. THIS IS THE BEST CHANCE FOR SNOW
IN THE PLAINS DURING THE EXTENDED PERIOD...THOUGH THE MODELS WILL
HAVE CHANCES FOR OROGRAPHIC SHOWERS AS THE FLOW ALOFT CONTINUES TO
BE FAIRLY MOIST.

TEMPERATURES WEDNESDAY THROUGH FRIDAY ARE GOING TO BE GOVERNED BY
A COUPLE OF FACTORS. DOWNSLOPE WINDS WILL BE FAVORED ACROSS THE
WESTERN AND CENTRAL ZONES BUT AIR WEST OF THE DIVIDE IS SO COLD
THAT THE WARMUP WILL BE MUCH SLOWER THAN NORMAL FOEHN WINDS WOULD
CREATE. ALSO...SNOW COVER WILL REGULATE A PART OF THE WARMUP AND
THE POSITION OF THE SURFACE TROUGH WILL SHOW THE EASTWARD EXTENT
OF THE BEST WARMING WITH TEMPERATURES STAYING COOLER EAST OF THE
TROUGH. BY THE WEEKEND THE PUSH WESTWARD OF THE COLD FRONT WILL
SUPPORT A DROP OF TEMPERATURES BUT AGAIN HOW FAR WEST AND HOW
DRAMATIC IS STILL NOT CERTAIN. WITH COLDER AIR POOLED UP WEST OF
THE DIVIDE WIND IS GOING TO BE A OMNIPRESENT FEATURE FOR THE
WESTERN ZONES. BORSUM

&&

.AVIATION...

FAST MOVING COLD FRONT WILL MOVE THROUGH EASTERN AND CENTRAL
MONTANA BRINGING INCREASED WINDS...BLOWING SNOW AND SNOW SHOWERS.
BEST CHANCE FOR SNOW WILL BE FOR EASTERN MONTANA WITH BLOWING SNOW
BEING THE BIGGEST PROBLEM FOR KBIL AND KLVM. VERY STRONG WINDS ARE
POSSIBLE FOR KLVM WITH DRIFTING AND BLOWING SNOW CREATING IFR
CONDITIONS AT TIMES. KBIL WILL SEE WINDS GUSTS TO 45 MPH WITH MVFR
CONDITIONS DUE TO BLOWING SNOW. KMLS WILL SEE LOWER CEILINGS IN
THE SNOW SHOWERS WITH IFR CONDITIONS AT TIMES. KSHR WILL SEE
CONDITIONS STAY MOSTLY VFR BUT WILL APPROACH MVFR CONDITIONS LATER
IN THE AFTERNOON. BORSUM

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY TUE     WED     THU     FRI     SAT     SUN
-------------------------------------------------------
BIL 019 014/023 005/029 020/033 018/034 015/034 024/036
    1/Q 16/S    51/B    11/B    11/B    11/B    11/B
LVM 016 010/022 007/026 020/032 021/034 019/032 024/033
    2/J 24/S    42/J    11/N    12/J    11/B    11/N
HDN 022 012/022 901/027 014/035 015/032 012/032 022/036
    2/J 28/S    51/B    11/B    11/E    11/B    12/B
MLS 020 009/016 907/023 010/031 013/026 010/028 020/035
    9/J 38/S    21/B    11/B    12/J    11/B    22/B
4BQ 020 011/020 903/022 011/034 017/031 012/032 023/036
    8/J 47/S    21/B    00/B    01/B    11/B    22/B
BHK 016 009/013 910/017 009/029 012/022 010/027 018/033
    9/J 56/S    11/B    01/B    11/B    11/E    12/B
SHR 023 008/024 901/027 014/036 016/034 014/033 022/038
    2/J 25/S    51/B    01/B    12/J    11/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 5 AM MST TUESDAY FOR
      ZONES 28-29-34-35-39-41-42-56-63-65-66.
     WIND CHILL ADVISORY IN EFFECT UNTIL 11 AM MST THIS MORNING
      FOR ZONES 30>33-36>38-57-58.
     WINTER WEATHER ADVISORY IN EFFECT FROM 11 AM THIS MORNING TO
      11 PM MST THIS EVENING FOR ZONES 30>33-36>38-57-58.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS