Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 140406
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
906 PM MST SAT DEC 13 2014

.UPDATE...

MINOR ADJUSTMENTS TO TEMPERATURES AND WINDS WITH THIS UPDATE.
PRECIPITATION CHANCES LOOK REASONABLE AFTER PREVIOUS UPDATE.
TEMPERATURES HOLDING JUST A BIT WARMER POST FRONTAL OVER CENTRAL
ZONES THANKS TO VERY GUSTY NORTHWEST WINDS. WINDS CURRENTLY
GUSTING TO NEAR 40 MPH IN BILLINGS OUT OF THE NORTHWEST. EXPECT
WINDS TO REMAIN GUSTY TONIGHT ACROSS THE AREA BUT SHOULD SEE GUSTS
DROP INTO THE 20 TO 30 MPH RANGE. ONCE WINDS DO BEGIN TO WEAKEN
PRECIPITATION WILL BEGIN TO INCREASE AND EVAPORATIVE COOLING WILL
HELP TEMPERATURES DROP. KEPT MIN TEMPERATURES PRETTY CLOSE TO
GOING FORECAST WITH JUST A FEW TWEAKS...BUT MADE ADJUSTMENT TO
HOURLY TEMPERATURE TRENDS TO REFLECT CURRENT TRENDS. CHAMBERS

&&

.SHORT TERM...VALID FOR SUN AND MON...

A COMPLICATED WEATHER PATTERN IS IN STORE FOR THE REMAINDER OF
THE WEEKEND AS DEEP WESTERN CONUS TROF BRINGS US COOLER WEATHER
AND AREAS OF ACCUMULATING SNOW...THOUGH WE WILL BE CUT OFF FROM
STRONG JET ENERGY IN THE SOUTHERN ROCKIES AND UNDER WEAK FLOW /
DEFORMATION ALOFT. LINGERING ENERGY ON BACK SIDE OF TROF IS
SLOWING ITS EASTWARD PROGRESSION WHICH IN TURN IS ALLOWING FOR
SOUTHERLY MOISTURE ADVECTION AS WE COOL ADVECT THE LOWER LEVELS
TONIGHT/SUNDAY. MUCH OF OUR REGION WILL SEE SOME SNOWFALL FROM
LATE TONIGHT THROUGH MONDAY MORNING DESPITE THE LACK OF STRONG
DYNAMICS. MODEL DIFFERENCES STILL EXIST SO BE AWARE OF POTENTIAL
FORECAST ADJUSTMENTS OVER THE NEXT 24 HOURS.

WX SHOULD BE FAIRLY QUIET FOR MOST OF TONIGHT AS WE REMAIN
BETWEEN STRONGER AREAS OF ASCENT TO OUR NW AND SOUTH. ENERGY
LIFTING THROUGH EASTERN UT AND WESTERN CO WILL APPROACH OUR SOUTH
LATE TONIGHT. MODELS ARE CONSISTENT IN SPREADING ISENTROPIC ASCENT
ALONG WITH 2-3 G/KG MIXING RATIOS TO OUR SOUTH CENTRAL PARTS BY
EARLY SUNDAY. EXPECT SNOW TO DEVELOP SOUTH TO NORTH LATER TONIGHT
WITH STRONGEST ASCENT EXPECTED TO BE EAST OF THE BEARTOOTH
ABSAROKAS. MODELS THEN DIVERGE WITH AREA OF STRONGER FORCING AND
GREATER QPF THROUGH SUNDAY NIGHT. GREATEST CONFIDENCE EXISTS IN
SHERIDAN AND SOUTHERN BIG HORN COUNTIES WITH THE COMBINATION OF
ISENTROPIC ASCENT...MID LEVEL FRONTOGENESIS AND LOW LEVEL UPSLOPE
FLOW. BELIEVE GREATEST SNOW AMOUNTS WILL BE IN THESE AREAS WITH AT
LEAST A FEW INCHES EXPECTED BY MONDAY MORNING. IMPACTS WILL BE
FURTHER COMPLICATED BY GUSTY NW WINDS FROM ABERDEEN HILL TO
SHERIDAN...THOUGH THE WIND WILL LIKELY LIMIT ACCUMS A BIT FOR THE
CITY OF SHERIDAN ITSELF. WILL ISSUE A WINTER WX ADVISORY FOR THESE
AREAS.

OTHER AREAS OF CONCERN INCLUDE MOSTLY OUR CENTRAL PARTS INCLUDING
THE CITY OF BILLINGS IF MID LEVEL WINDS BACK ENOUGH TO REDUCE
DOWNSLOPE IMPACTS...SUCH AS THE NAM/ECMWF/CANADIAN SUGGEST. WILL
STAY THE COURSE WITH A MODEL CONSENSUS AND GIVE AREAS SURROUNDING
THE ADVISORY AREA 1-3 INCHES OF ACCUMULATION INCLUDING THE
BEARTOOTH FOOTHILLS TO THE WEST AND BROADUS TO THE EAST. GREATEST
POTENTIAL FOR SNOW ACCUMULATION WILL BE SUNDAY NIGHT AS SNOWFALL
DURING THE DAY ON SUNDAY WILL BATTLE SFC TEMPS IN THE 30S. TRAVEL
OVER PASSES SUCH AS ARROW CREEK HILL...LAME DEER DIVIDE...HYSHAM
HILLS AND MAYBE UP AT BULL MTN DIVIDE WILL BE MOST PRONE TO SEE
DIFFICULT TRAVEL CONDITIONS. HAVE RAISED POPS AND SNOW AMOUNTS
ACROSS MUCH OF THESE AREAS GIVEN THE INCREASED CONFIDENCE TODAY.

SYSTEM WILL WIND DOWN MONDAY MORNING AS ANOTHER SHORTWAVE OUT OF
SASKATCHEWAN BRINGS DRIER AIR FROM THE NORTH. GIVEN EXPECTATION OF
SOME SNOW COVER HAVE LOWERED TEMPS MONDAY AND MONDAY NIGHT AS
FAIRLY WEAK CANADIAN SFC RIDGE SLIDES INTO THE NORTHERN PLAINS.
COULD SEE A COUPLE DAYS OF BELOW NORMAL TEMPERATURES EARLY NEXT
WEEK WHICH WE HAVE NOT SEEN IN AWHILE.

JKL

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

MODELS ARE IN DECENT AGREEMENT FOR MOST OF THE EXTENDED PERIOD
BUT DO DIVERGE TOWARD THE END OF NEXT WEEK INTO NEXT WEEKEND.
HOWEVER...FORECASTER CONFIDENCE IS SOMEWHAT LOW IN THE DETAILS. A
TROUGH MOVING ONTO THE PACIFIC NORTHWEST COAST COMBINED WITH AN
UPPER LOW OVER MINNESOTA WILL RESULT IN A HIGH AMPLITUDE RIDGE
ACROSS THE STATE TUESDAY.

MODELS THEN SHOW A SPLIT FLOW ALOFT ACROSS THE CENTRAL AND
NORTHERN ROCKIES WEDNESDAY AND THURSDAY KEEPING THE BULK OF THE
ENERGY TO OUR NORTH AND SOUTH. MODELS DIVERGE BY FRIDAY AS THE
PACIFIC SYSTEM MOVES ONSHORE WITH THE GFS CUTTING OFF THE UPPER
LOW INTO SOUTHERN CALIFORNIA BY SATURDAY WHILE THE ECMWF KEEPS AN
OPEN WAVE ACROSS THE CENTRAL AND NORTHERN ROCKIES. IN ANY
CASE...THE OVERALL PATTERN AT THIS TIME IS NOT CONDUCIVE FOR ANY
SIGNIFICANT PRECIPITATION NOR ANY ARCTIC AIR INVASION. HOOLEY


&&

.AVIATION...

CLOUDS WILL BE ON THE INCREASE THIS EVENING AS A DISTURBANCE
APPROACHES THE FORECAST AREA. RAIN AND SNOW SHOWER CHANCES WILL
INCREASE THIS EVENING WITH THE BEST CHANCES AFTER 06Z. THE BEST
CHANCES FOR RAIN AND SNOW SHOWERS WILL BE ALONG AND WEST OF
ROUNDUP-KBIL-KSHR LINE. MVFR AND ISOLATED IFR CONDITIONS WILL BE
POSSIBLE IN ANY SHOWER ACTIVITY. VFR CONDITIONS ARE EXPECTED EAST
OF THIS LINE. THE MOUNTAINS WILL BE OBSCURED WITH FREQUENT SNOW
SHOWER ACTIVITY. HOOLEY


&&

.PRELIMINARY POINT TEMP/POPS...

    SUN     MON     TUE     WED     THU     FRI     SAT
-----------------------------------------------------------
BIL 033/037 022/030 016/031 018/036 020/039 021/039 021/038
    46/S    62/S    01/B    11/B    11/B    11/U    11/B
LVM 031/036 019/035 016/037 022/040 024/040 021/039 020/038
    83/S    21/B    01/B    11/B    11/B    11/B    11/B
HDN 029/037 020/032 010/031 011/034 013/036 014/038 013/037
    57/S    72/S    00/U    11/B    11/B    11/U    11/B
MLS 031/035 022/029 014/029 012/030 014/032 015/034 013/034
    26/S    61/B    10/B    10/B    01/B    10/U    11/B
4BQ 031/036 022/030 012/033 013/035 014/036 015/037 014/037
    25/S    63/S    10/U    10/B    01/B    11/U    01/B
BHK 029/033 020/028 012/028 012/030 014/032 016/032 014/034
    24/S    42/S    11/B    00/B    11/B    10/U    01/B
SHR 030/035 019/031 010/032 012/035 014/037 013/036 013/037
    68/S    83/S    10/U    10/B    11/B    10/U    01/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT FROM 3 AM SUNDAY TO 11 AM
      MST MONDAY FOR ZONE 38.
WY...WINTER WEATHER ADVISORY IN EFFECT FROM 3 AM SUNDAY TO 11 AM
      MST MONDAY FOR ZONE 99.
     WINTER WEATHER ADVISORY IN EFFECT UNTIL 11 AM MST MONDAY FOR
      ZONE 98.

&&

$$
WEATHER.GOV/BILLINGS



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