Winter Storm in Montana, January 30 to 31, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
327 AM MST WED JAN 30 2013

.SHORT TERM...VALID FOR TDY AND THU...

PICTURE IS BECOMING A BIT MORE CLEAR IN THE SHORT TERM PERIOD.

DOWNSLOPE WARMING HAS COMMENCED ALONG OUR WESTERN FOOTHILLS AS
LEE SIDE PRESSURE FALLS CONTINUE. WIND GUSTS IN EXCESS OF 30 MPH
AND TEMPS IN THE MID TO UPPER 20S OBSERVED AT LIVINGSTON AND BIG
TIMBER AT 3 AM. THESE LEE SIDE PRESSURE FALLS PER 40-50 KT NWLY
MID LEVEL FLOW AHEAD OF NEXT SHORTWAVE FROM THE NORTH WILL RESULT
IN STRONG DOWNSLOPING AND A PERIOD OF WARMER CONDITIONS ACROSS OUR
WEST TODAY...AND NOW BELIEVE THIS WARMING WILL REACH BILLINGS AT
LEAST FOR A FEW HOURS TODAY. HAVE RAISED HIGHS TO 30-35 ACROSS OUR
WEST. COLD AIR WILL REMAIN ENTRENCHED IN OUR EAST WITH HIGHS IN
THE UPPER SINGLE DIGITS TO LOW TEENS...BUT EVEN THIS AIRMASS WILL
MODERATE SLIGHTLY AS NEXT MORE POTENT ARCTIC FRONT DROPS OUT OF
CANADA. IN THE MEANTIME...WIND SPEEDS HAVE DROPPED TO 10 MPH OR
LESS IN OUR EAST SO HAVE CANCELLED THE WIND CHILL ADVISORY FOR
CUSTER... FALLON AND CARTER. THESE AREAS WILL BE PRONE TO ANOTHER
ROUND OF COLD WIND CHILLS AGAIN TONIGHT INTO THURSDAY.

COLD FRONT WILL SURGE BACK INTO THE AREA LATE TODAY AND
TONIGHT...AND TEMPS WILL FALL AS WINDS SHIFT TO THE NORTH THEN
EAST. 850MB TEMPS TO -25C EXPECTED NEAR THE DAKOTAS BORDER BY
EARLY THURSDAY...AND GIVEN STRONG LEE SIDE PRESSURE RISE MAX THERE
IS A CHANCE THAT THIS FRONT WILL BACK ALL THE WAY TO LIVINGSTON
LATE TONIGHT...THOUGH THIS IS NOT A CERTAINTY. BILLINGS TEMPS WILL
DROP QUICKLY BACK TO THE SINGLE DIGITS TONIGHT AS WE WILL SEE
FIRST HAND THE BATTLE BETWEEN THE TWO AIRMASSES.

WATER VAPOR IMAGERY SHOWS A NICE MOISTURE TAP COMING INTO THE BC
COAST...WITH NW FLOW SHORTWAVE DROPPING THRU WESTERN CANADA. MOIST
NWLY ISENTROPIC ASCENT WILL BRING A PERIOD OF SNOWFALL TO MUCH OF
THE AREA TODAY INTO THURSDAY...BEGINNING IN THE WESTERN MTNS EARLY
THEN ENHANCING IN OUR CENTRAL PARTS LATER TODAY AS THE FRONT SAGS
BACK INTO THE AREA. NW FLOW ALOFT...LOW LEVEL CONVERGENCE AND DEEP
DENDRITIC LAYER ALL SUGGEST A MORE SIGNIFICANT SNOWFALL FOR OUR
SOUTH CENTRAL PARTS...WITH DRIER/COLDER AIR TO THE EAST AND
DOWNSLOPING WINDS TO THE WEST. THIS WILL IMPACT I-90 FROM HARDIN
TO SHERIDAN AND HIGHWAY 212 OVER LAME DEER DIVIDE. BELIEVE SNOW
WILL SHIFT INTO BILLINGS TONIGHT PER THE BACKDOOR FRONT AND
DEEPENING COLD AIR/UPSLOPE FLOW. SHOULD SEE A COUPLE INCHES IN THE
BILLINGS AREA BUT MUST STILL STRESS UNCERTAINTY PENDING EVOLUTION
OF SFC FRONT. THE BIG HORNS AND NW ASPECTS OF THE CRAZY AND
ABSAROKA MOUNTAINS WILL ALSO BE FAVORED FOR SNOWFALL OVER THE NEXT
36 HOURS. OUR WESTERN LOWER ELEVATIONS SUCH AS BIG TIMBER...
LIVINGSTON AND RED LODGE WILL BE LARGELY SHELTERED BY THE
DOWNSLOPING...BUT COULD SEE A LITTLE ACCUMULATION OVER PARK COUNTY
ONCE THE STRONGER ASCENT WORKS IN LATER TODAY. SNOW EVENT WILL
TAPER OFF BY MIDDAY THURSDAY AS HEIGHTS BEGIN TO RISE FROM THE
WEST. EXPECT A WIDE RANGE OF TEMPS ON THURSDAY WITH 30S IN OUR
WEST AND ONLY SINGLE DIGITS ALONG THE DAKOTAS BORDER. AS FOR
BILLINGS...THINK WE WILL STAY UNDER THE INFLUENCE OF THE COLDER
SFC RIDGE UNTIL LATE IN THE DAY...THEN A GOOD CHANCE OF RISING
TEMPS THURSDAY NIGHT AS SFC TROF FINALLY SHIFTS EAST AND SW WINDS
STRENGTHEN. WEAK SHORTWAVE IN THE BACKING FLOW ALOFT MAY BRING
SOME LIGHT SNOW SHOWERS LATE THURSDAY NIGHT AS TEMPS RISE.

JKL

.LONG TERM...VALID FOR FRI...SAT...SUN...MON...TUE...

FRIDAY WILL SEE THE DEPARTURE OF THE ARCTIC INTO THE DAKOTAS BUT
NOT BEFORE A SHORTWAVE IN NORTHWEST FLOW ALOFT FORCES SOME SHOWER
ACTIVITY. DEFINITELY WILL SEE WARMING TEMPERATURES ACROSS THE EAST
AND WITH MOST OF THE PRECIP FALLING INTO DOWNSLOPING WINDS DO NOT
EXPECT MUCH IN THE WAY OF AMOUNTS. SHOULD SEE 15 TO 20 DEGREE
TEMPERATURE INCREASES ACROSS THE CENTRAL AND EASTERN ZONES WITH
THE WEST BEING WINDY AND MIXED WITH TEMPERATURES IN THE 40S.

UPPER LEVEL RIDGE WEST OVER THE PACIFIC NORTHWEST ON SATURDAY
BEGINS TO SHIFT EAST AND FLATTEN THROUGH SUNDAY. THIS SUPPORTS
CONTINUALLY FALLING SURFACE PRESSURES EAST OF THE CONTINENTAL
DIVIDE AND TIGHTENS WIND GRADIENTS FOR GAP FLOW AREAS. THIS WILL
BRING DRY AND WARMER CONDITIONS BUT AM STAYING A BIT BELOW
GUIDANCE AS DRAINAGE FLOWS AND EXISTING SNOW COVER COULD LIMIT
FULL WARMING.

MONDAY A TROUGH BEGINS BUILDING ALONG THE WEST COAST AND HEIGHTS
BUILD AGAIN ACROSS THE REGION. STRONG FLOW ALOFT OVER THE CANADIAN
ROCKIES KEEPS LEESIDE TROUGHING IN PLACE SO EXPECT WIND TO BE
UNYIELDING FOR LIVINGSTON AND NYE FOR MOST OF THE EXTENDED. THIS
PATTERN PERSISTS WITH FLUCUATIONS IN THE SURFACE TROUGH STRENGTH
THROUGH TUESDAY. MODELS TRY TO DEVELOP A CUTOFF LOW ALONG THE WEST
COAST LATER IN THE EXTENDED BUT INITIALLY THIS JUST KEEPS THE
RIDGE IN PLACE WITH DRY AND MILD WEATHER WEDNESDAY. BORSUM
&&

.AVIATION...

ARCTIC AIRMASS ENTRENCHED OVER EASTERN MONTANA WILL RETREAT FROM
THE FOOTHILLS BACK TO CENTRAL AREAS TODAY AND THEN MAKE A SURGE
BACK TO THE WEST TONIGHT. MOISTURE OVERRUNNING THIS BOUNDARY WILL
GENERATE SNOW AND THIS WILL BE FAVORED ALONG A KSHR-KBIL AXIS.
ALONG THIS BOUNDARY MVFR AND OCCASIONAL IFR CONDITIONS WILL BE
POSSIBLE LATER TODAY AS A BAND OF SNOW SHOWERS DEVELOP. TO THE
EAST...ONLY ISOLATED SNOW SHOWERS AND MVFR CONDITIONS ARE
EXPECTED. TO THE WEST GUSTY WEST WINDS WILL DOMINATE FOR THE DAY
LIMITING PRECIPITATION BUT THE ARCTIC IS LIKELY TO RETURN TONIGHT
BRINGING INCREASED SNOW SHOWER ACTIVITY. BORSUM
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY THU     FRI     SAT     SUN     MON     TUE
-------------------------------------------------------
BIL 030 006/027 022/042 023/042 028/046 028/046 026/048
    6/S 75/S    22/J    00/B    01/N    11/N    11/B
LVM 035 020/039 030/041 025/042 030/043 029/046 030/048
    5/S 64/S    22/W    11/N    11/N    11/N    11/N
HDN 024 005/022 018/041 017/040 020/043 025/043 023/045
    8/S 87/S    22/J    00/U    01/U    11/U    11/U
MLS 011 911/009 008/035 016/037 019/040 023/039 023/041
    7/S 64/S    22/J    10/B    01/U    01/B    11/U
4BQ 015 905/013 009/037 016/039 020/041 024/041 021/043
    8/S 97/S    22/J    00/U    00/U    01/B    00/U
BHK 007 918/002 902/033 017/034 019/037 020/037 021/039
    5/S 41/B    12/J    10/B    00/U    01/B    11/B
SHR 025 005/026 017/039 016/041 017/043 023/044 025/046
    7/S 87/S    22/W    00/U    00/U    01/U    01/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL NOON MST THURSDAY FOR
      ZONES 38-57-58.
WY...WINTER WEATHER ADVISORY IN EFFECT UNTIL NOON MST THURSDAY FOR
      ZONES 98-99.

&&

WEATHER.GOV/BILLINGS

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