Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 181630
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
930 AM MST THU DEC 18 2014

.UPDATE...
WEAK UPPER LEVEL LOW OVER SOUTH CENTRAL NORTH DAKOTA IS WEAKENING
RAPIDLY THIS MORNING. LIGHT SNOW OVER THE FAR EASTERN ZONES HAS
ENDED AND HAVE REMOVED POPS FOR THE REMAINDER OF THE MORNING.
LEE-SIDE TROUGH HAS SET UP AHEAD OF AN APPROACHING SHORT WAVE AND
THIS HAS ALLOWED WINDS TO INCREASE IN LIVINGSTON. OCCASIONAL
WINDS GUSTS OF 30 KTS CAN BE EXPECTED THROUGH THE DAY. DID LOWER
TEMPERATURES IN BILLINGS TODAY AS SURFACE ANALYSIS SHOWING COLD
AIR OVER THE BIGHORN BASIN IN WYOMING. SURFACE GRADIENT WILL ALLOW
THIS COLD AIR TO FEED INTO THE CLARKS FORK AND THIS WILL RESULT IN
COOLER AIR ADVECTING INTO BILLINGS. BUFKIT ALSO INDICATING
SOUTHWEST WINDS IN BILLINGS THROUGH THE DAY SO HAVE BACKED OFF ON
HIGHS TO THE UPPER 30S. REST OF THE FORECAST ON TRACK. RICHMOND

&&

.SHORT TERM...VALID FOR TDY AND FRI...

SATELLITE IS SHOWING AN UPPER LEVEL LOW SPINNING SOUTHEAST ACROSS
THE SOUTHEAST PORTIONS OF THE STATE. THIS WEAK DISTURBANCE WILL
BRING A SLIGHT CHANCE FOR SOME FLURRIES ACROSS THE FALLON AND
CARTER COUNTIES THROUGH MID MORNING. CAN`T RULE OUT SOME ISOLATED
POCKETS OF FOG AS WELL ACROSS THE EAST. HOWEVER...THERE IS A BIT
MORE MIXING THAN THE PAST FEW MORNINGS SO ONLY SOME ISOLATED AREAS
ARE EXPECTED THROUGH MID MORNING. OTHERWISE...WEAK LEE-SIDE
TROUGHING WILL SET UP ACROSS OUR FORECAST AREA TODAY RESULTING IN
SOME WIND FOR THE LIVINGSTON AREA AND ADJACENT BEARTOOTH/ABSAROKA
FOOTHILLS. HOWEVER...WINDS ARE NOT EXPECTED TO BECOME STRONG
THOUGH.

AN AMPLIFIED HIGH PRESSURE RIDGE WILL BE OVER THE STATE FRIDAY
BRINGING DRY CONDITIONS ALONG WITH SLIGHTLY WARMER TEMPERATURES. A
SURFACE LOW OVER SOUTHWEST CANADA WILL BRING CONTINUED LEE-SIDE
TROUGHING ACROSS OUR AREA THROUGH THE DAY KEEPING WINDY CONDITIONS
ACROSS THE FOOTHILLS LOCATIONS. AS THE LOW MOVES EAST FRIDAY NIGHT
INTO SATURDAY MORNING IT WILL SWING A PACIFIC FRONT ACROSS THE
AREA...BRINGING A CHANCE FOR SNOW SHOWERS FRIDAY NIGHT INTO
SATURDAY. THERE`S NOT MUCH IF ANY TEMPERATURE DIFFERENCE BEHIND
THE FRONT ON SATURDAY AS READINGS WILL BE SIMILAR TO TODAY AND
FRIDAY WITH MOST LOCATIONS IN THE UPPER 30S TO LOWER 40S. HOOLEY

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

AN ACTIVE EXTENDED PERIOD ESPECIALLY FOR AREA MOUNTAINS. STILL
LOOKS LIKE SOME POTENTIAL FOR SNOW CHRISTMAS EVE INTO CHRISTMAS
DAY.

FOR THIS WEEKEND...SURGE OF PACIFIC MOISTURE PLOWS INTO THE
NORTHERN ROCKIES ON THE NOSE OF A STRONG 160KT JET STREAM. THESE
STRONG JET STREAM WINDS EXTEND HALF WAY ACROSS THE PACIFIC OCEAN
SO WILL SEE A PROLONGED PERIOD OF MOISTURE ADVECTION INTO THE AREA
AS THIS FEATURE WILL PERSIST OVER THE AREA INTO WEDNESDAY. FOR
SATURDAY AND SUNDAY THE JET STREAM WILL BE ORIENTED IN A ZONAL
MANNER WHICH WILL ALLOW LEE SIDE TROFFING AND DOWNSLOPE WARMING TO
BOOST TEMPERATURES WELL ABOVE SEASONAL LEVELS. THIS WOULD NORMALLY
BE A FAIRLY DRY PATTERN BUT THE AMOUNT OF PACIFIC MOISTURE WILL
BRING AT LEAST A CHANCE OF PRECIPITATION TO MOST LOCATIONS...WITH
LIKELY POPS FOR AREA MOUNTAINS ON WEST FACING SLOPES. DESPITE THE
WARM NATURE OF THIS SYSTEM COULD STILL SEE 6 TO 12 INCHES OF SNOW
BY THE END OF THE WEEKEND ON THOSE WEST FACING SLOPES. FOR LOWER
ELEVATIONS THE WARMTH DURING THE DAY WILL PROVIDE MAINLY RAIN AS A
PRECIPITATION TYPE...HOWEVER OVERNIGHT AND INTO THE MORNING HOURS
CAN`T RULE OUT SOME VALLEY FREEZING RAIN OVER SOUTHEAST MONTANA.

EARLY NEXT WEEK...AS WE GET INTO EARLY NEXT WEEK THE ORIENTATION
OF THE JET VEERS MORE NORTHERLY THANKS TO A SUBTROPICAL RIDGE
SLIDING EAST OUT OF HAWAII INTO THE EASTERN PACIFIC OFF
CALIFORNIA. THE STRENGTH OF THE JET DENOTES THE PRESENCE OF COLDER
AIR OVER CANADA WHICH WILL BE ALLOWED TO DROP SOUTHWARD ONCE THE
JET ORIENTATION SHIFTS MORE NORTHERLY ACROSS THE AREA.
TEMPERATURES ON SUNDAY WILL BE NEAR 50 DEGREES IN SOME AREAS BUT
DROP INTO THE 30S BY TUESDAY AND INTO THE UPPER 20S TO LOWER 30S
ON WEDNESDAY. PACIFIC MOISTURE WILL CONTINUE TO FLOW OVER THE AREA
DURING THIS PERIOD KEEPING A CHANCE OF PRECIPITATION IN THE
FORECAST EACH DAY. BEST CHANCES WILL REMAIN IN THE MOUNTAINS BUT
WITH A SHIFT TOWARD THE NORTHERN SLOPES SEEING THE HIGHEST
POPS/SNOW ACCUMULATIONS.

CHRISTMAS EVE/CHRISTMAS DAY...SPLIT IN THE JET OVER THE CENTRAL
PACIFIC LOOKS TO DRIVE THE DEVELOPMENT OF A STRENGTHENING RIDGE
OVER ALASKA FROM WEDNESDAY INTO NEXT WEEKEND. THIS INFLUENCE
DEVELOPS A STRONG KINK IN THE JET OVER THE PACIFIC NORTHWEST ON
WEDNESDAY THAT DROPS INTO THE NORTHERN AND CENTRAL ROCKIES
WEDNESDAY NIGHT INTO THURSDAY AS A DEEPENING STORM SYSTEM. LATEST
PROGS HAVE TRENDED SOUTHWARD...WITH THE BULK OF THIS SYSTEM
HITTING WYOMING WITH THE HEAVIEST SNOWFALL ON THE 00Z RUNS.
HOWEVER THERE IS STILL PLENTY OF TIME FOR A SHIFT IN TRACK AND
STRENGTH WITH THIS SYSTEM. EVEN WHERE IT CURRENTLY IS PROGGED
THERE IS STILL A 20 TO 40 PERCENT CHANCE OF SOME SNOW CHRISTMAS
EVE INTO CHRISTMAS DAY WITH DIFFLUENT SOUTHERLY FLOW ALOFT
COMBINED WITH UPSLOPE SURFACE GRADIENT. WILL HAVE TO KEEP A CLOSE
EYE ON THIS SYSTEM AS THE DOOR TO COLD CANADIAN AIR IS OPEN AND
THERE IS PLENTY OF PACIFIC MOISTURE AVAILABLE TO DEVELOP A
SIGNIFICANT SNOWFALL SOMEWHERE IN THE INTER-MOUNTAIN WEST AND
FRONT RANGE...WHETHER THAT IS OVER MONTANA OR COLORADO IS STILL
IN QUESTION. THOSE PLANNING TRAVEL WEDNESDAY INTO THE WEEKEND
SHOULD BE ALERT TO CHANGES IN THE FORECAST THAT COULD IMPACT
TRAVEL CONDITIONS.

LOOKING OUT JUST A BIT FURTHER THE LATEST ECMWF...AND TO AN
EXTENT THE GFS...HINTS AT AN ARCTIC INTRUSION ON THE HEELS OF
THIS POTENTIAL CHRISTMAS SYSTEM. CHAMBERS


&&

.AVIATION...

LINGERING PATCHY FOG/LOW CLOUD NEAR THE DAKOTAS BORDER WILL
DISSIPATE BY MIDDAY. VFR FLIGHT CONDITIONS WILL OTHERWISE PREVAIL
TODAY AND TONIGHT WITH SCATTERED TO BROKEN MID AND HIGH CLOUD.
MOUNTAINS WILL BE OBSCURED AT TIMES WITH A FEW SNOW SHOWERS OVER
THE HIGH TERRAIN. SOUTHWEST WINDS WILL BE GUSTY AT TIMES ALONG THE
FOOTHILLS INCLUDING KLVM WITH GUSTS OF 25-35 KTS. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY FRI     SAT     SUN     MON     TUE     WED
-------------------------------------------------------
BIL 038 025/041 029/041 029/046 038/044 026/039 020/032
    0/B 00/B    22/W    24/W    32/W    22/W    22/J
LVM 041 025/042 029/045 030/048 039/047 026/043 019/038
    1/N 11/N    31/B    35/W    44/W    32/W    22/J
HDN 037 015/037 020/040 020/045 031/043 019/038 014/032
    0/B 00/B    22/W    14/W    32/W    22/J    22/J
MLS 038 018/039 022/041 023/044 030/040 023/037 018/030
    0/B 00/B    12/W    03/W    22/W    22/W    11/E
4BQ 041 017/040 019/042 021/046 030/042 021/038 016/033
    0/B 00/B    12/W    03/W    22/W    22/J    11/B
BHK 035 017/037 019/042 020/043 025/038 021/034 015/028
    1/B 00/B    12/J    03/W    22/J    22/J    11/E
SHR 040 015/038 020/040 019/043 032/042 019/039 015/036
    0/B 11/U    12/J    03/W    33/W    22/J    22/J

&&

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

&&

$$
WEATHER.GOV/BILLINGS


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