Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 221734
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
1034 AM MST MON DEC 22 2014

.UPDATE...
TWO AREAS OF SNOW THIS MORNING. EASTERN AREAS SEEING BAND OF SNOW
ON THE INCREASE AND WRAP AROUND MOISTURE CONTINUES TO MOVE TOWARDS
THE AREA. BAND OF SNOW OVER WESTERN AREAS IS TRANSITORY AND
FIGHTING TEMPERATURES NEAR FREEZING SO NOT SEEING MUCH IN THE WAY
OF ACCUMULATIONS. DID UP POPS FOR WESTERN AREAS AND LOWER POPS FOR
BILLINGS AREA. UPDATE SENT. BORSUM

&&

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

ACTIVE WEATHER PATTERN CONTINUES THROUGH THE SHORT
TERM...ALTHOUGH MOST OF OUR FORECAST AREA WILL BE QUIETER THAN
SUNDAY. A NORTHWEST FLOW ALOFT WITH EMBEDDED PIECES OF ENERGY WILL
MOVE SOUTHEAST ACROSS OUR AREA TODAY. THE MAIN WEATHER FEATURE FOR
TODAY WILL BE A STRONG SURFACE LOW PRESSURE OVER EASTERN SOUTH
DAKOTA AND NEBRASKA THIS AFTERNOON INTO THIS EVENING. THE LOW WILL
STRENGTHEN DURING THE DAY RESULTING IN TIGHT PRESSURE GRADIENTS
AS FAR WEST AS EASTERN MONTANA AND WYOMING. THIS WILL RESULT IN
WINDY CONDITIONS ACROSS MAINLY THE EASTERN HALF OF OUR FORECAST
AREA. HOWEVER...IT WILL BE WINDY ACROSS OUR ENTIRE ENTIRE BUT NOT
AS MUCH AS WAS THE CASE SUNDAY. A STRONG VORT MAX DIVES SOUTH OUT
OF CANADA AND ACROSS THE MONTANA/DAKOTA BORDERS THIS AFTERNOON AND
EVENING. MOISTURE ON THE FRONT SIDE OF THE LOW WILL GET PULLED
NORTH AND WESTWARD WRAPPING BACK ON THE BACK SIDE OF THE LOW
ACROSS MAINLY FALLON CARTER AND CARTER COUNTIES. ALTHOUGH THE
LATEST MODELS RUNS HAVE BROUGHT SOME OF THE HEAVIER QPF AMOUNTS
WEST INTO THE EASTERN PORTIONS OF CUSTER AND POWDER RIVER
COUNTIES.

GGW RADAR IS STARTING TO FILL IN DURING THE PAST COUPLE OF HOURS
WITH MOVEMENT SOUTH/SOUTHEAST. TIMING BRINGS THE SNOW INTO CUSTER
AND FALLON COUNTY AROUND DAYBREAK OR SLIGHTLY THEREAFTER. WILL NOT
MAKE ANY CHANGES TO THE WINTER WEATHER ADVISORY FOR FALLON AND
CARTER COUNTIES WHICH IS CURRENTLY IN EFFECT EVEN THOUGH THE SNOW
LOOKS TO START LATER THAN PREVIOUSLY ANTICIPATED. GIVEN THAT
MODELS BRING THE QPF FURTHER WEST AND WPC IS BRINGING THE 2-4 INCH
SNOW AMOUNTS INTO EASTERN CUSTER AND POWDER RIVER COUNTIES...WILL
ADD THESE TWO COUNTIES TO THE ADVISORY WITH A START TIME OF 9 AM.
THE SYSTEM LOOKS TO BE A QUICK MOVER WITH THE SNOW EXPECTED TO END
AFTER MIDNIGHT TONIGHT. ELSEWHERE ACROSS THE FORECAST
AREA...EXPECT A WINDY DAY WITH A SLIGHT CHANCE FOR A SNOW SHOWER.

THE LOW PULLS EAST TUESDAY WITH PRESSURE GRADIENTS SLACKENING
ACROSS OUR EAST. HOWEVER...ANOTHER SURFACE LOW SETS UP ACROSS
SOUTHERN B.C. DURING THE AFTERNOON AND THIS WILL ALLOW FOR LEE-
SIDE TROUGHING TO RE-DEVELOP ACROSS OUR AREA. PRESSURE GRADIENTS
TIGHTEN CONSIDERABLY BY TOMORROW EVENING/NIGHT ACROSS OUR WESTERN
AREAS AND THIS WILL BRING ANOTHER ROUND OF STRONG WINDS TO
LIVINGSTON AND THE BEARTOOTH/ABSAROKA FOOTHILLS. HAVE INCREASED
WINDS IN THE GRIDS TO ADVISORY LEVELS BUT WILL HOLD OFF ON ANY
STATEMENTS WITH THIS ISSUANCE. TEMPERATURES THE NEXT COUPLE OF
DAYS WILL RUN AT OR SLIGHTLY ABOVE NORMAL FOR THE NEXT COUPLE OF
DAYS. HOOLEY

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

GFS CONTINUES TO BE THE OUTLIER FOR THE CHRISTMAS SYSTEM THIS
MORNING. THE NAM WINDOW IS NOW TOUCHING THE CHRISTMAS TIME FRAME
AND IT AND THE SREF MEAN ARE IN SUPPORT OF THE ECMWF SOLUTION
WITH THE CANADIAN NOT TOO FAR OFF. WPC GUIDANCE SUPPORTS A BLEND
OF EC/NAM FOR TIMING AND PRECIPITATION AND SEE NO REASON TO
DEVIATE FROM THIS AS THE EC HAS BEEN THE MORE CONSISTENT MODEL
OVER THE PAST FEW DAYS. CONSISTENCY WAS GOOD LAST NIGHT BUT THIS
DISSIPATED WHEN THE 06Z GFS CAME IN AND SHIFTED ITS SOLUTION NORTH
AND SLOWED ARRIVAL OF THE COLDER CANADIAN AIRMASS. THE GFS
CONTINUES TO HOLD ONTO THIS SOLUTION WHICH HOLDS OFF SNOW 18 HOURS
LATER THAN OTHER MODELS DUE TO A SECONDARY SURFACE LOW THAT MOVES
OUT OF IDAHO AND ACROSS CENTRAL MONTANA WEDNESDAY NIGHT INTO
THURSDAY MORNING. THE OTHER MODELS HAVE A MORE TRADITIONAL SURFACE
PATTERN WITH A SURFACE LOW DROPPING INTO WYOMING IN ONE PIECE
WEDNESDAY EVENING. BOTH MODEL SETS BRING PRECIPITATION AND COLDER
AIR TO THE AREA...THE GFS JUST BRINGS IT IN FOR CHRISTMAS
AFTERNOON AND NIGHT WHILE THE PREFERRED MODEL CONSENSUS IS FOR A
LATE WEDNESDAY NIGHT INTO THURSDAY TIMING. WHILE CONSISTENCY
BETWEEN THE GFS AND OTHER MODELS IS POOR THE CONSISTENCY BETWEEN
THE OTHER MODEL SOLUTIONS IS GOOD. SO WILL LEAN ON THIS MIX FOR
THE CURRENT FORECAST PACKAGE...BUT WILL LEAVE SOME ROOM FOR THE
SLOWER GFS POSSIBILITY.

WEDNESDAY WILL BE A WARM AND IN SOME LOCATIONS A WINDY DAY. ZONAL
FLOW ALOFT WILL SUPPORT LEE SIDE TROF AND POTENTIALLY STRONG WINDS
FOR LIVINGSTON...NYE...BIG TIMBER AND POSSIBLY HARLOWTON. PACIFIC
MOISTURE TRAPPED IN THIS WESTERLY FLOW COULD BRING A FEW SNOW
SHOWERS TO THE WESTERN MOUNTAINS BUT BY AND LARGE WEDNESDAY WILL
BE DRY. DISTURBANCE DROPS INTO THE PACIFIC NORTHWEST WEDNESDAY
AFTERNOON AND BY WEDNESDAY EVENING JET DIVERGENCE INCREASES AND
PULLS CANADIAN COLD FRONT SOUTHWARD AND THROUGH THE AREA
OVERNIGHT. EXPECT TO SEE SNOW DEVELOP OVER NORTHERN AND WESTERN
ZONES BEFORE MIDNIGHT...SPREADING SOUTH AND EAST DURING THE
OVERNIGHT HOURS. AS COLD AIR DEEPENS UP AND NORTHERLY WINDS
UPSLOPE INTO THE MOUNTAINS WILL SEE SNOW INTENSITY INCREASE. LOOKS
LIKE THE HEAVIEST SNOW WILL BE FROM 3 AM THROUGH EARLY AFTERNOON.
2 TO 4 INCHES OF SNOW SEEMS REASONABLE FOR MUCH OF THE AREA BY
CHRISTMAS AFTERNOON...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE. THE
FOOTHILLS AROUND RED LODGE AND SHERIDAN COULD GO OVER 6 INCHES
BASED ON LATEST QPF AND SNOW RATIO PROJECTIONS. WILL PROBABLY NEED
SOME WINTER HIGHLITES FOR THIS SYSTEM BUT WILL WAIT UNTIL WE
HOPEFULLY GET MORE MODEL AGREEMENT BEFORE WORKING THAT OUT.

AREA WILL BE UNDER A TROF IN NORTHERLY FLOW ON FRIDAY WHICH WILL
KEEP TEMPERATURES COOL. WILL KEEP LOW PRECIPITATION CHANCES IN THE
FORECAST BUT WOULDN`T EXPECT ANY ACCUMULATION WITH IT. SATURDAY
WILL SEE SOME WEAK RIDGING ALOFT FOR DRY CONDITIONS AND A BIT
WARMER TEMPERATURES. MODELS HINTING AT A COLDER SYSTEM FOR THE END
OF THE WEEKEND WITH THE POTENTIAL FOR HIGH TEMPERATURES IN THE
SINGLE DIGITS AND LOWER TEENS FOR EARLY NEXT WEEK. STILL TOO MUCH
UNCERTAINTY TO DROP TEMPERATURES THAT FAR RIGHT NOW BUT DID TREND
TEMPERATURES LOWER AND ADDED IN A CHANCE OF SNOW FOR SUNDAY INTO
MONDAY TO GET FOOT IN THE DOOR.

FOR HOLIDAY TRAVELERS...TUESDAY LOOKS LIKE THE BEST TRAVEL DAY
ACROSS THE NORTHERN ROCKIES. WEDNESDAY DOESN`T LOOK TOO BAD OVER
SOUTHERN MONTANA EITHER BUT AREAS NORTH AND WEST WILL BE SEEING
INCREASING SNOW CHANCES. FOR CHRISTMAS EVE AND CHRISTMAS DAY
EXPECT SNOW THAT COULD MAKE TRAVEL DIFFICULT. CHAMBERS
&&

.AVIATION...

UNSTABLE NORTHWEST FLOW OVER THE AREA WILL KEEP SHOWER ACTIVITY
GOING THROUGH THE DAY TODAY IN MOST LOCATIONS. HEAVIER PRECIPITATION
IS EXPECTED ALONG AND EAST OF A MILES CITY TO BROADUS LINE. MVFR
CONDITIONS WILL DEVELOP BY MID DAY AS SNOW INTENSIFIES...
PRODUCING LOCAL IFR CONDITIONS...ALONG WITH BLOWING AND DRIFTING
SNOW. PERIODS OF SNOW IN THE MOUNTAINS WILL KEEP MOUNTAIN
OBSCURATION GOING INTO TONIGHT AS WELL FOR ALL AREA MOUNTAINS. VFR
CONDITIONS WILL PREVAIL ACROSS THE REST OF THE AREA...WITH MVFR
CONDITIONS POSSIBLE WITH LIGHT SNOW SHOWERS. WEST TO NORTHWEST
WINDS WILL BE GUSTY AGAIN TODAY WITH GUSTS 30 TO 40KTS ACROSS THE
REGION. CHAMBERS/REIMER

&&

.PRELIMINARY POINT TEMP/POPS...

    TDY TUE     WED     THU     FRI     SAT     SUN
-------------------------------------------------------
BIL 042 025/039 026/041 028/031 012/025 012/029 018/027
    3/W 20/N    02/R    77/S    31/B    11/B    23/S
LVM 037 014/034 023/039 025/031 012/028 011/031 018/030
    4/W 20/N    02/R    88/S    52/S    12/S    23/S
HDN 040 022/037 019/040 026/031 010/025 010/028 015/027
    3/W 30/B    12/R    77/S    32/S    11/B    23/S
MLS 034 021/035 019/040 026/030 013/023 009/028 013/024
    7/S 31/B    12/R    65/S    21/E    11/B    23/S
4BQ 034 024/034 017/040 025/031 014/024 007/027 013/027
    8/S 82/S    11/B    66/S    32/S    11/B    13/S
BHK 032 024/029 015/038 022/028 008/019 007/025 009/021
    8/S 72/S    12/O    44/S    21/B    11/B    23/S
SHR 038 025/036 018/041 026/033 012/026 008/031 013/029
    4/W 41/B    01/B    77/S    42/S    11/B    14/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 5 AM MST TUESDAY FOR
      ZONES 32-33-36-37.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS



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