Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 112139
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
339 PM MDT FRI APR 11 2014

.SHORT TERM...VALID FOR SAT AND SUN...

A BREEZY EVENING ON TAP ACROSS THE AREA AHEAD OF COLD FRONT THAT
WILL MOVE INTO THE AREA LATE TONIGHT. THE FRONT IS CURRENTLY NORTH
NORTH OF THE CANADIAN BORDER BUT WILL MOVE QUICKLY SOUTH TONIGHT
AS STRONG JET STREAM SHIFTS SOUTH OF THE AREA. COMBINATION OF
GUSTY WINDS AND CIRRUS CLOUD COVER WILL HELP HOLD TEMPERATURES IN
THE LOWER 40S IN MANY SPOTS TONIGHT. MODELS GENERATE SOME LIFT
OVER SOUTHERN HALF OF THE AREA IN THE EARLY MORNING HOURS WITH
STRENGTHENING 700MB FRONTOGENESIS SO DID ADD SOME LOW
PRECIPITATION CHANCES IN BEFORE SUNRISE...BUT THINK MOST AREAS
WILL STAY DRY UNTIL MID TO LATE MORNING TOMORROW.

A STRONG AND BROAD VORTICITY AREA DROPS SOUTHWARD OUT OF BC AND THROUGH
WESTERN MONTANA AND IDAHO DURING THE DAY TOMORROW. THIS SPREADS A
DIFFLUENT FLOW ALOFT OVER THE WESTERN HALF OF THE FORECAST AREA.
UNDERNEATH THIS DIFFLUENCE THE SHIFTING OF THE JET STREAM SOUTH OF
THE AREA ALLOWS A CANADIAN SURFACE HIGH TO BUILD IN TO THE AREA
WITH COLDER AIR AND GUSTY NORTHEASTERLY UPSLOPE WINDS. UPSLOPE
COMBINED WITH DIFFLUENCE ALOFT WILL BE A GOOD PRECIPITATION
PRODUCER FOR THE AREA FROM SATURDAY AFTERNOON THROUGH SUNDAY
MORNING WITH OVER A QUARTER INCH OF PRECIPITATION FORECAST WEST OF
A ROUNDUP TO BROADUS LINE...AND OVER AN INCH EXPECTED IN THE
MOUNTAINS. AS COLDER AIR BUILDS INTO THE AREA SATURDAY AFTERNOON
RAIN WILL TURN TO SNOW ABOVE 5000 FEET AND WILL START TO SEE
ACCUMULATIONS ON GRASSY SURFACES IN THE FOOTHILLS. SNOW WILL
CONTINUE HEAVY AT TIMES SATURDAY NIGHT FOR FOOTHILLS AND MOUNTAIN
LOCATIONS...AND SNOW LEVELS WILL FALL TO THE LOWER ELEVATIONS
ACROSS THE PLAINS BY MIDNIGHT SATURDAY NIGHT.

SNOW ACCUMULATIONS...FOR MOUNTAIN LOCATIONS ONE TO TWO FEET OF
SNOW ARE POSSIBLE WITH THE HEAVIEST SNOW ON THE NORTH AND EAST
SLOPES. FOOTHILLS ABOVE 5000 FEET ARE LOOKING AT 6 TO 12 INCHES OF
SNOW. BETWEEN 4000 AND 5000 FEET 3 TO 6 INCHES ARE POSSIBLE.
AREAS AS LOW AS BILLINGS LIKELY TO SEE SOME LIGHT SNOW
ACCUMULATION BY SUNRISE SUNDAY. ISSUED A WINTER STORM WATCH FOR
SOUTHERN MOUNTAINS AND BEARTOOTH FOOTHILLS ZONES STARTING AT NOON
TOMORROW THROUGH SUNDAY AFTERNOON. EXPECT TO NEED SOME WINTER
WEATHER ADVISORIES WITH THIS EVENT AS WELL AND HAVE ADVISORY TYPE
SNOW ACCUMULATIONS IN SOME AREAS IN THE CURRENT FORECAST. HOWEVER
THE METRO MODEL SUGGESTS MOST AREAS OUTSIDE THE FOOTHILLS WILL SEE
ROADS STAY MAINLY WET WELL INTO SATURDAY NIGHT. AS A RESULT
IMPACTS WITH THIS EVENT IN THE LOWER ELEVATIONS LOOK FAIRLY
MINIMAL WITH THE BIGGEST THREATS BEING POOR VISIBILITY AND
RANCHING INTERESTS. WILL LET THE MID SHIFT TAKE A LOOK AT
OVERNIGHT MODELS TO REFINE WHERE TO PUT ANY ADDITIONAL HIGHLITES
WITH THIS SYSTEM.

VORTICITY CONTINUES TO PRESS SOUTHWARD INTO THE GREAT BASIN
SATURDAY NIGHT INTO SUNDAY BEFORE SHIFTING EAST BRINGING A
SIGNIFICANT SNOW EVENT TO COLORADO. THIS TRAJECTORY SHOULD BRING A
FAIRLY QUICK END TO PRECIPITATION SUNDAY MORNING WITH LINGERING
UPSLOPE SNOW SHOWERS FOR FOOTHILLS AND MOUNTAINS. WITH COOL HIGH
PRESSURE OVER THE AREA TEMPERATURES WILL BE QUITE COOL SUNDAY AND
SUNDAY NIGHT COULD SEE LOWS IN THE TEENS IN MANY AREAS. CHAMBERS


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

MONDAY WILL BE A DRY AND WARMER DAY AS HEIGHTS RISE BEHIND TROF
DEPARTING TO OUR SE. DOWNSLOPE WINDS SHOULD ALLOW FOR TEMPS TO
RECOVER BACK TO THE 50S/NEAR 60F ACROSS OUR WEST AND CENTRAL
PARTS...BUT 40S MAY HOLD NEAR THE DAKOTAS BORDER. OVERALL A QUIET
WEATHER DAY.

MODELS HAVE HAD A DIFFICULT TIME OF LATE WITH REGARD TO EVOLUTION
OF NEXT PACIFIC TROF...BUT TODAY/S RUNS HAVE COME MORE IN LINE...
SHOWING PACIFIC ENERGY MOVING THRU THE NRN ROCKIES WITH A
DEVELOPING WNW JET. COMBINATION OF PACIFIC TROF/HEIGHT FALLS AND
FEED OF NE WINDS/COOLER AIR ASSOCIATED WITH HUDSON BAY LOW/
CYCLONIC FLOW TO OUR NE WILL ALLOW FOR INCREASING CHANCES OF PCPN
FROM LATE TUESDAY THROUGH WEDNESDAY NIGHT. SO WITH SOME IMPROVED
CONFIDENCE HAVE RAISED POPS TO ABOVE CLIMATOLOGY FOR THESE
PERIODS. IN FACT...THE GFS/ECMWF/CANADIAN ALL SHOW 850MB TEMPS
FALLING BELOW ZERO BY TUESDAY NIGHT OR EARLY WEDNESDAY...AND THIS
IS PLAUSIBLE GIVEN THE TAP OF COOLER CANADIAN AIR JUST TO OUR NE.
SO CANNOT RULE OUT SOME WET SNOWFALL ACROSS OUR LOWER ELEVATIONS.
IN LINE WITH THE HIGHER POPS HAVE ALSO LOWERED TEMPERATURES ON
WEDNESDAY... WHICH AT THIS TIME LOOKS LIKE THE COOLEST DAY OF THE
WEEK.

ZONAL FLOW WITH POTENTIAL ADDITIONAL WEAK PACIFIC SHORTWAVE
ACTIVITY WARRANTS SLIGHT POPS CONTINUING THRU THU/FRI...BUT WITH A
TREND UP IN TEMPS. OVERALL WEATHER PATTERN WILL REMAIN ACTIVE AS
ONE WOULD EXPECT IN MID APRIL.

AS FOR TEMPS...50S TO LOW 60S ON TUESDAY WILL GIVE WAY TO A MUCH
COOLER WEDNESDAY...WITH HIGHS STAYING IN THE 40S IF NOT COOLER.
WEST FLOW SHOULD ALLOW FOR A MODERATION IN TEMPS BY THE END OF THE
WEEK...AT LEAST BACK TOWARD NORMAL AND IN THE 50S OR LOW 60S.

JKL
&&

.AVIATION...

GUSTY WEST WINDS WILL IMPACT KLVM INTO THIS EVENING WITH GUSTS OF
35-40 KTS. MIXED GUSTS OF 15-25 KTS WILL BE FELT AT OTHER TAF
SITES UNTIL SUNSET. A CANADIAN COLD FRONT WILL BRING A FEW SHOWERS
TO THE AREA TONIGHT...BUT VFR WILL PREVAIL.

ON SATURDAY... CHANCES OF PCPN AND SUB-VFR FLIGHT CONDITIONS WILL
INCREASE THROUGH THE DAY AS A WEATHER SYSTEM DROPS OUT OF CANADA.
EXPECT LOWER ELEVATION RAIN SHOWERS AND HIGH ELEVATION SNOW WITH
AREAS OF MVFR TO IFR AND MOUNTAIN OBSCURATIONS...ESPECIALLY BY
AFTERNOON. WINDS WILL SHIFT TO THE NORTH AND NORTHEAST TOMORROW
BEHIND A FRONTAL PASSAGE LATE TONIGHT.

JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    SAT     SUN     MON     TUE     WED     THU     FRI
-----------------------------------------------------------
BIL 043/047 028/038 024/056 035/061 036/048 032/054 038/057
    28/R    84/O    10/U    02/W    43/W    32/W    22/W
LVM 038/047 026/038 021/057 033/060 035/050 032/056 037/056
    2+/R    +6/O    10/U    02/W    44/W    33/W    33/W
HDN 042/050 029/040 024/057 031/062 034/050 031/054 033/059
    27/R    83/O    10/U    02/W    43/W    32/W    22/W
MLS 038/050 027/040 024/053 029/057 032/048 029/050 032/056
    23/R    32/O    10/U    01/B    44/W    32/W    22/W
4BQ 043/051 027/039 023/053 028/059 032/049 029/050 032/057
    15/R    44/O    10/U    02/W    34/W    32/W    22/W
BHK 037/049 024/036 021/047 024/049 027/045 024/044 029/055
    22/R    22/O    10/U    00/B    34/W    22/W    22/W
SHR 041/048 026/035 019/051 029/060 033/051 032/053 035/058
    18/R    +7/S    20/U    02/W    33/W    32/W    22/W

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH IN EFFECT FROM SATURDAY AFTERNOON THROUGH
      SUNDAY AFTERNOON FOR ZONES 56-66-67.
WY...WINTER STORM WATCH IN EFFECT FROM SATURDAY AFTERNOON THROUGH
      SUNDAY AFTERNOON FOR ZONE 98.

&&

$$
WEATHER.GOV/BILLINGS



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