Winter Storm in Wyoming, November 14 to 15, 2010

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
918 PM MST SUN NOV 14 2010

.SHORT TERM...VALID FOR MON AND TUE...

MADE AN UPDATE TO ISSUE A WINTER WEATHER ADVISORY ALONG THE EAST
SLOPES FROM NYE TO RED LODGE AND IN THE PARADISE VALLEY SOUTH OF
LIVINGSTON FOR TONIGHT. REPORTS AROUND RED LODGE WERE INDICATING
2 TO 3 INCHES OF SNOW ALREADY ON THE GROUND WITH 2 TO 4 INCHES
SOUTH OF LIVINGSTON. ANOTHER COUPLE OF INCHES EXPECTED FOR A
TOTAL OF 4 TO 7 BY MORNING. SNOW SHOULD DECREASE TOWARD MORNING
AS THE NEXT UPSTREAM WAVE EXITS THE AREA. TWH

PREVIOUS DISCUSSION... UNSTABLE NORTHWEST FLOW PROVING A
CHALLENGE THIS EVENING. NORTHWEST FACING SLOPES HAVE RECEIVED 2-5
INCHES OF SNOW IN THE HIGHER TERRAIN FOR THE DAY. THE EAST SLOPES
OF THE ROCKIES FROM MCLEOD TO NYE TO RED LODGE HAVE HAD A STEADY
STREAM OF SNOW SHOWERS THIS AFTERNOON AND EVENING EVEN THOUGH THE
LOW LEVEL FLOW WAS WEAKLY DOWNSLOPE. ONE SHORTWAVE WAS MOVING
THROUGH THE AREA AT THE MOMENT. RADAR RETURNS ALONG THE EAST
SLOPES SHOULD DIMINISH THIS EVENING AND SNOW LIGHTEN UP A BIT.
ANOTHER SHORTWAVE WAS PUSHING SOUTHEAST FROM NORTH CENTRAL
MONTANA AND WILL BRING ANOTHER SHOT OF PRECIPITATION. THE SECOND
WAVE WILL PUSH PRECIPITATION A LITTLE FARTHER EAST OFF THE PLAINS
AND THIS WILL BE THE BEST SHOT FOR THE CENTRAL ZONES. ADJUSTED
POPS THIS EVENING FOR ABOVE AND RAISED POPS A BIT OVERNIGHT.
BUMPED SNOW AMOUNTS UP ALONG THE EAST SLOPES AND OVER THE HIGHER
TERRAIN. HIT THE NORTHWEST SLOPES HARDEST WITH A TOTAL OF 3 TO 6
ADDITIONAL INCHES TONIGHT. BILLINGS WILL HAVE A GOOD SHOT OF A
RAIN AND SNOW MIX EARLY BECOMING ALL SNOW TONIGHT. HARD TO TELL
ON ACCUMULATION BUT WOULD EXPECT TO SEE AT LEAST A DUSTING
OVERNIGHT FROM SNOW SHOWERS. SNOW ADVISORY LOOKS GOOD FOR THE BIG
HORNS AS SNOW WILL PICK UP WITH UPSTREAM WAVE MOVING IN. UPDATE
OUT SHORTLY. TWH

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

MODELS WERE IN GENERAL AGREEMENT WITH THE PATTERN IN THE EXTENDED
PERIOD AND FAIRLY CONSISTENT FROM RUN-TO-RUN. HAVE MADE A FEW
ADJUSTMENTS TO THE FORECAST DUE TO INCREASING CONFIDENCE. A STRONG
PACIFIC JET WILL BE OVER THE REGION WED INTO FRI BEFORE A POSITIVELY
TILTED TROUGH ROTATES INTO THE AREA. WEAK RIDGING/ZONAL FLOW WILL BE
OVER THE AREA WED AND WED NIGHT...THEN THE FLOW WILL BECOME
GRADUALLY SW WITH TIME WITH ENERGY INCREASING IN THE FLOW AHEAD OF
THE NEXT TROUGH. LOW PRESSURE WAS FORECAST TO MOVE E ALONG THE
MT/CANADIAN BORDER THROUGH THU WITH WARM ADVECTION OVER THE AREA. A
WARM FRONT AND ASSOCIATED MOISTURE WILL BRING A SLIGHT CHANCE OF
SNOW SHOWERS TO THE REGION ON WED. WED NIGHT WILL BE MAINLY DRY...
BEFORE PRECIPITATION CHANCES START TO INCREASE W AND N OF KBIL AHEAD
OF A COLD FRONT ON THU. RAISED TEMPERATURES WED AND THU DUE TO THE
WARM ADVECTION AND PREFRONTAL AIRMASS.

AN ARCTIC COLD FRONT WILL PLUNGE S INTO THE AREA THU NIGHT. THE
LOW-LEVEL FLOW WILL TURN TO AN EASTERLY UPSLOPE DIRECTION WHILE THE
COLD AIRMASS REMAINS ENTRENCHED OVER THE AREA THROUGH SAT NIGHT.
PLENTY OF PACIFIC MOISTURE WILL MOVE INTO THE AREA DURING THIS TIME
AROUND THE PACIFIC UPPER TROUGH/LOW. HAD POPS ABOVE CLIMATOLOGICAL
VALUES DURING THIS PERIOD WITH THE HIGHEST PRECIPITATION CHANCES
OVER THE SW MOUNTAINS IN THE PATH OF THE BEST MOISTURE. PRECIPITATION
TYPE ACROSS THE FORECAST AREA WOULD BE ALL SNOW DUE TO THE COLD
AIRMASS. POPS CAN BE FURTHER REFINED AS THIS PERIOD GETS CLOSER IN
TIME. HAVE TRENDED TEMPERATURES TOWARD THE COLDEST
GUIDANCE...WHICH WAS MAINLY THE WEIGHTED CYCLE GFS...DURING THIS
PERIOD AS MODELS AGREED THAT 850 MB TEMPERATURES WILL FALL INTO
THE -10 TO -12 DEGREE C RANGE WITH TIME. THE MODELS BROUGHT AN
EVEN COLDER SURGE OF AIR INTO THE AREA IN THE SUN/SUN NIGHT TIME
FRAME WITH 850 MB TEMPERATURES IN THE TEENS C BELOW ZERO. THUS
HAVE GONE WITH WELL BELOW NORMAL TEMPERATURES LATE IN THE PERIOD.
A FAIR AMOUNT OF MOISTURE WILL REMAIN OVER THE REGION AS THE UPPER
TROUGH MOVES OVER THE AREA. ARTHUR

&&

.AVIATION...

PRECIP IN IN WESTERN ZONES...IS SLOWLY SHIFTING EAST LATE THIS
EVENING...AND WILL CONTINUE TO SPREAD INCREASING CHANCES FOR PRECIP
FROM WEST TO EAST ACROSS ALL ROUTES OVERNIGHT. EXPECT PRECIP TO BE
MAINLY SNOW...BUT A RAIN SNOW MIX WILL BE POSSIBLE IN SOME AREAS
UNTIL AROUND 06Z. MAINLY VFR TO MVFR RANGE FLIGHT CONDITIONS WILL
BE REDUCED TO IFR AND LIFR CONDITIONS DUE TO REDUCED VISIBILITIES
IN SNOW. PRECIP IS EXPECTED TO CLEAR FROM WEST TO EAST THROUGH THE
DAY MONDAY...MAINLY AFTERNOON. MOUNTAIN OBSCURATIONS CAN BE EXPECT
TO CONTINUE OVER AREA MOUNTAIN RANGES OVERNIGHT AND THROUGH MUCH
OF THE DAY MONDAY. GILSTAD

&&

.PRELIMINARY POINT TEMP/POPS...

    MON     TUE     WED     THU     FRI     SAT     SUN
-----------------------------------------------------------
BIL 033/047 034/040 022/038 028/046 024/029 017/023 010/019
    75/W    68/W    42/J    11/B    22/S    32/S    22/S
LVM 035/042 032/037 020/034 028/040 027/033 016/027 009/022
    73/W    77/W    22/J    12/W    23/S    43/S    23/S
HDN 025/048 031/040 022/038 022/044 018/031 018/028 010/021
    76/W    6+/J    42/J    11/B    22/S    22/S    22/S
MLS 028/043 027/039 020/034 016/043 019/028 015/026 011/020
    56/W    49/J    62/J    11/B    22/S    22/S    22/S
4BQ 026/043 029/039 022/036 017/047 021/034 017/030 015/024
    66/W    39/J    62/J    11/B    22/S    22/S    22/S
BHK 024/038 025/038 018/029 013/037 015/027 015/023 011/021
    36/W    39/J    62/J    11/B    22/S    22/S    22/S
SHR 026/042 026/041 020/035 019/044 021/040 018/036 009/028
    76/W    56/J    42/J    11/B    22/S    22/S    22/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 5 AM MST MONDAY FOR
      ZONES 56-64-66.
WY...WINTER WEATHER ADVISORY IN EFFECT UNTIL MIDNIGHT MST MONDAY
      NIGHT FOR ZONE 98.

&&

WEATHER.GOV/BILLINGS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
919 PM MST SUN NOV 14 2010

MTZ028>042-056>058-063>068-WYZ098-099-160500-
SOUTHERN WHEATLAND-MUSSELSHELL-TREASURE-NORTHERN ROSEBUD-CUSTER-
FALLON-NORTHERN STILLWATER-YELLOWSTONE-POWDER RIVER-CARTER-
SOUTHERN BIG HORN-EASTERN CARBON-NORTHERN PARK-
NORTHERN SWEET GRASS-GOLDEN VALLEY-RED LODGE FOOTHILLS-
NORTHERN BIG HORN-SOUTHERN ROSEBUD-JUDITH GAP-PARADISE VALLEY-
LIVINGSTON AREA-BEARTOOTH FOOTHILLS-ABSAROKA/BEARTOOTH MOUNTAINS-
CRAZY MOUNTAINS-NORTHEAST BIG HORN MOUNTAINS-SHERIDAN FOOTHILLS-
919 PM MST SUN NOV 14 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...SOUTH CENTRAL MONTANA...SOUTHEAST MONTANA AND NORTH
CENTRAL WYOMING.

.DAY ONE...TONIGHT

A MOIST AND UNSTABLE NORTHWEST FLOW WILL BRING ACCUMULATING SNOW
TO THE HIGH COUNTRY TONIGHT. THE HARDEST HIT AREA WILL BE THE BIG
HORN MOUNTAINS WHERE HEAVY SNOW WILL BE LIKELY AT TIMES LATE
TONIGHT THROUGH TUESDAY. ACCUMULATING SNOW IS ALSO EXPECTED ALONG
THE EAST SLOPES TONIGHT FROM THE PARADISE VALLEY TO MCLEOD TO NYE
TO RED LODGE WHERE 4 TO 7 INCHES OF TOTAL SNOW IS EXPECTED BY
MONDAY MORNING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

PERIODS OF ACCUMULATING SNOW WILL CONTINUE OVER THE MOUNTAINS
MONDAY AND TUESDAY...ESPECIALLY THE BIG HORN MOUNTAINS WHERE
HEAVY SNOW WILL BE LIKELY AT TIMES THROUGH MONDAY EVENING.

IN ADDITION...STRONG SOUTHWEST WINDS WILL DEVELOP AT LIVINGSTON
AND ALONG THE FOOTHILLS OF THE BEARTOOTH MOUNTAINS MONDAY NIGHT
INTO TUESDAY. DANGEROUS CROSS WINDS ARE POSSIBLE ALONG INTERSTATE
90 IN THE LIVINGSTON AREA.

A STRONG COLD FRONT WILL BRING GUSTY WEST TO NORTHWEST WINDS AND
THE POTENTIAL FOR SNOWFALL ACROSS THE LOWER ELEVATIONS TUESDAY
AND TUESDAY NIGHT. AT THIS TIME...IT APPEARS THE GREATEST CHANCE
OF ACCUMULATING SNOW WILL BE EAST OF BILLINGS. COLDER AIR WILL
SURGE INTO THE AREA TUESDAY NIGHT AND LINGER INTO WEDNESDAY.

AFTER A BRIEF WARM UP WITH WINDY CONDITIONS THURSDAY...ANOTHER
COLD FRONT HAS THE POTENTIAL TO BRING WIDESPREAD SNOWFALL AND
COLDER TEMPERATURES FRIDAY INTO NEXT WEEKEND.

PEOPLE IN SOUTHERN MONTANA AND NORTHERN WYOMING SHOULD REVIEW
THEIR WINTER SAFETY PLANS. IT IS A GOOD TIME TO EVALUATE IF
VEHICLES ARE PREPARED FOR WINTER TRAVEL...INCLUDING SNOW BRUSHES
AND EMERGENCY SUPPLIES. ANYONE WITH OUTDOOR ACTIVITIES OR TRAVEL
PLANNED NEXT WEEKEND SHOULD MONITOR THE LATEST FORECASTS AND
STATEMENTS AS THE WEATHER PATTERN IS SHAPING UP TO BE QUITE
ACTIVE.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.