Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 191051
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
351 AM MST FRI DEC 19 2014

.SHORT TERM...VALID FOR TDY AND SAT...

MODELS FOR THE SHORT TERM CONTINUE TO BE IN A GOOD AGREEMENT AND
CONSISTENT SO NOT MANY CHANGES HAVE BEEN MADE WITH THE PREVIOUS
FORECAST. AN AMPLIFIED HIGH PRESSURE RIDGE WILL BE OVER OUR
FORECAST AREA TODAY BRINGING DRY CONDITIONS ALONG WITH MILD
TEMPERATURES FOR THIS TIME OF YEAR. A SLIGHT CHANCE FOR SNOW
SHOWERS WILL CONTINUE TODAY FOR THE BEARTOOTH/ABSAROKA MOUNTAINS
AS A SYSTEM ACROSS THE PACIFIC NORTHWEST APPROACHES. WEAK LEE-SIDE
TROUGHING WILL CONTINUE TODAY INTO TONIGHT RESULTING IN WINDY
CONDITIONS FROM BILLINGS WESTWARD BUT ADVISORY WINDS ARE NOT
EXPECTED.

THIS RIDGE WILL BE BRIEF AS ANOTHER TROUGH AND PACIFIC FRONT MOVE
ACROSS THE WESTERN HALF OF OUR FORECAST AREA TONIGHT AND ACROSS
THE EAST DURING THE DAY SATURDAY. WILL CONTINUE WITH CURRENT TREND
OF CHANCES FOR RAIN AND SNOW SHOWERS THIS EVENING AND TONIGHT FROM
BILLINGS WESTWARD THEN SHIFTING EAST DURING THE DAY SATURDAY.
SOUNDINGS SHOW TEMPERATURES AT THE SURFACE BELOW FREEZING WITH A
SMALL POCKET OF WARM AIR JUST ABOVE THE SURFACE LATE TONIGHT INTO
SATURDAY MORNING FROM ABOUT BILLINGS EASTWARD SO SOME FREEZING
RAIN SHOWERS MAY BE POSSIBLE DURING THIS TIME. MUCH STRONGER LEE-
SIDE TROUGHING SETS UP SATURDAY NIGHT INTO SUNDAY RESULTING IN
TIGHT PRESSURE GRADIENTS FOR THE UPPER YELLOWSTONE AND STILLWATER
VALLEYS. THIS WILL RESULT IN THE LIKELIHOOD OF STRONG WINDS FROM
ABOUT BIG TIMBER TO LIVINGSTON AND THE ADJACENT FOOTHILLS. HOOLEY

.LONG TERM...VALID FOR SUN...MON...TUE...WED...THU...

THE EXTENDED IS PUNCTUATED BY SNOW IN THE HIGH COUNTRY AND THE
POTENTIAL FOR LOWER ELEVATION SNOW CHRISTMAS EVE AND CHRISTMAS
DAY. TEMPERATURES WILL TREND FROM WELL ABOVE NORMAL TO START THE
HOLIDAY WEEK TO BELOW NORMAL BY CHRISTMAS.

SUNDAY AND MONDAY...STRONG AND LENGTHY WESTERLY PACIFIC JET
STREAM WILL PUSH INTO THE AREA DURING THE WEEKEND FROM THE WEST. A
SUBSTANTIAL MOISTURE TAP ASSOCIATED WITH THE JET WILL BRING
SIGNIFICANT SNOW TO AREA MOUNTAINS THROUGH THE WEEKEND INTO EARLY
NEXT WEEK. SNOW WILL BE CONCENTRATED MAINLY ON WEST FACING SLOPES
AND THE MOUNTAINS AROUND COOKE CITY COULD SEE OVER A FOOT OF SNOW
DURING THE SATURDAY THROUGH MONDAY TIME FRAME...AND LOCALLY
HEAVIER ACCUMULATIONS WILL BE POSSIBLE. WINDS COMBINED WITH THIS
HEAVY WET SNOWFALL MAY RESULT IN SOME AVALANCHE ISSUES SUNDAY INTO
EARLY NEXT WEEK AS WELL. SOME SNOW WILL LIKELY SLOP OVER THE
MOUNTAINS ONTO THE EAST SLOPES BUT DOWNSLOPE WARMING WILL LIMIT
ACCUMULATIONS IN THESE AREAS. ACROSS THE PLAINS THERE WILL BE
ENOUGH DOWNSLOPE WARMING TO PUSH TEMPERATURES TO NEAR 50 DEGREES
SUNDAY AND MONDAY OVER WESTERN AND CENTRAL ZONES. DESPITE THIS
DOWNSLOPE THERE IS SO MUCH MOISTURE THAT WIDESPREAD 30 AND 40 POPS
SEEM REASONABLE SUNDAY...WITH 30 POPS ON MONDAY. PRECIPITATION
TYPE WILL BE TRICKY FOR THE LOWER ELEVATIONS WITH THIS SYSTEM AND
WILL LIKELY SEE A MIX OF RAIN/SNOW WEST OF BILLINGS WITH A
RAIN/FREEZING RAIN/SNOW MIX TO THE EAST. BEST CHANCES FOR FREEZING
RAIN WILL BE LATE NIGHT INTO THE MORNING HOURS SUNDAY AND MONDAY.
WHILE ANY AMOUNT OF FREEZING RAIN WILL BE A TRAVEL CONCERN...AT
THIS POINT NOT SEEING A REASON TO CHANGE TRAVEL PLANS...BUT IF
YOU ARE PLANNING TRAVEL SUNDAY AND MONDAY KEEP TABS ON THE LATEST
FORECAST FOR ANY CHANGES TO THIS THINKING.

TUESDAY...PACIFIC JET GETS TILTED TO THE NORTHWEST TUESDAY WHICH
SHUNTS BEST MOISTURE FEED NORTH OF THE AREA. THUS WILL SEE
PRECIPITATION CHANCES DECREASE TUESDAY. HOWEVER THERE IS STILL
ENOUGH MOISTURE AND INSTABILITY AROUND TO SUPPORT AT LEAST A
SLIGHT CHANCE FOR RAIN OR SNOW ACROSS THE AREA TUESDAY AND TUESDAY
NIGHT. EXPECT GUSTY WINDS ALONG THE FRONT RANGE INCLUDING I-90
AROUND LIVINGSTON.

WEDNESDAY INTO CHRISTMAS...MODELS IN BETTER AGREEMENT WITH THE
OVERALL PATTERN FOR THIS TIME FRAME. GFS SHIFTED MORE TOWARD THE
ECMWF SOLUTION THOUGH IT GOES A BIT FARTHER SOUTH WITH THE
STRONGEST ENERGY. AS A RESULT THE GFS DEVELOPS A STORM SYSTEM OVER
MAINLY SOUTHERN WYOMING AND COLORADO WHILE THE ECMWF IS A BIT
FURTHER NORTH. BOTH SOLUTIONS BRING A GLANCING BLOW OF QG FORCING
TO THE AREA WEDNESDAY NIGHT INTO EARLY THURSDAY AND BOTH HAVE A
GOOD UPSLOPE GRADIENT AS COLDER CANADIAN AIR PUSHES IN FROM THE
NORTH. ALL THIS ADDS UP TO A GOOD CHANCE FOR SNOW CHRISTMAS EVE
NIGHT THROUGH MUCH OF THE DAY CHRISTMAS ALONG AND SOUTH OF A
ROUNDUP TO BROADUS LINE...WITH SNOW SHOWERS OVER THE REST OF THE
AREA. AT THIS POINT THE HIGHEST IMPACT SNOWFALL LOOKS TO STAY
SOUTH OF THE AREA WITH JUST LIGHT ACCUMULATIONS OVER OUR AREA
(FOOTHILLS ZONES POSSIBLY EXCEPTED). HOWEVER THIS SYSTEM IS STILL
WELL OUT IN THE EXTENDED AND SHOWS SIGNS OF DEVELOPING INTO A
STRONG SNOWSTORM SO WILL NEED TO KEEP A CLOSE EYE ON IT OVER THE
WEEKEND. THOSE WITH TRAVEL PLANS...ESPECIALLY TO THE SOUTH SHOULD
STAY TUNED TO THE LATEST FORECAST AND BE ANTICIPATING SOME WINTER
DRIVING CONDITIONS.

TEMPERATURES ON CHRISTMAS WILL BE BELOW SEASONAL LEVELS IN THE
20S. YESTERDAY MODELS WERE HINTING AT A MUCH COLDER PUSH OF ARCTIC
AIR FOR THE WEEKEND. THE LATEST RUNS HAVE BACKED OFF OF THIS
SOLUTION. HOWEVER NORTHERLY FLOW WILL REMAIN OVER THE AREA WHICH
HINTS AT CONTINUED BELOW NORMAL TEMPERATURES THROUGH CHRISTMAS
WEEKEND. CHAMBERS

&&

.AVIATION...

VFR CONDITIONS WILL PREVAIL TODAY. EXPECT INCREASING MID AND HIGH
LEVEL CLOUD COVER FROM THE WEST...WITH INCREASING CHANCES FOR RAIN
SHOWERS IN LOWER ELEVATIONS WEST OF BILLINGS BY EVENING. SNOW
SHOWERS WILL DEVELOP OVER WESTERN MOUNTAINS WITH LOCAL MVFR TO IFR
CONDITIONS NEAR PRECIPITATION ALONG WITH OCCASIONAL MOUNTAIN
OBSCURATION. BY EVENING MOUNTAIN SNOW WILL BECOME MORE PERSISTENT
WITH IFR OR LOWER CONDITIONS AND MOUNTAIN OBSCURATION BECOMING
PREDOMINANT. WINDS OVER WESTERN FOOTHILLS INCLUDING KLVM WILL GUST
30 TO 40KTS OUT OF THE SOUTHWEST TODAY INTO TONIGHT. CHAMBERS
&&

.PRELIMINARY POINT TEMP/POPS...

    TDY SAT     SUN     MON     TUE     WED     THU
-------------------------------------------------------
BIL 041 029/042 031/045 033/042 026/041 025/035 019/027
    0/B 41/B    24/O    23/R    22/O    22/S    43/S
LVM 042 028/042 033/041 033/041 024/038 021/034 016/025
    1/N 31/N    34/O    44/O    32/S    23/S    54/S
HDN 037 020/039 020/043 031/041 025/039 023/034 017/027
    0/B 32/J    14/O    23/R    23/O    22/S    34/S
MLS 039 022/040 022/041 027/038 023/035 023/032 013/024
    0/B 23/J    14/O    22/O    22/S    32/S    22/S
4BQ 040 019/041 021/041 028/039 022/035 023/033 014/025
    0/B 13/J    13/O    22/O    22/S    32/S    33/S
BHK 036 018/039 021/037 026/034 019/032 023/029 010/020
    0/B 13/W    05/O    22/S    21/B    32/S    22/S
SHR 038 022/040 020/041 030/040 023/037 022/034 014/025
    1/U 22/J    13/O    23/O    32/S    22/S    55/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS


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