Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 150353
AFDBYZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
853 PM MST SUN DEC 14 2014

.UPDATE...

MINOR ADJUSTMENTS TO THE GOING FORECAST THIS EVENING.
PRECIPITATION HAS TRENDED AS EXPECTED...HOWEVER SNOW ACCUMULATIONS
ARE LAGGING BEHIND WHAT WOULD BE EXPECTED. BILLINGS PICKED UP A
TENTH OF AN INCH OF PRECIPITATION IN THE PAST FEW HOURS WITH ABOUT
EIGHT TENTHS OF AN INCH OF SNOW ACCUMULATION. WHATS BOTHERING US
RIGHT NOW IS THE SIZE OF THE SNOWFLAKES. THERE IS ABOUT A 5KFT
DEEP DENDRITIC LAYER OVER THE AREA RIGHT NOW BUT ITS AT THE TOP OF
THE SATURATED COLUMN AROUND 12KFT AND MAY NOT BE IN A POSITION TO
HELP SNOW GROWTH THE WAY WE EXPECTED EARLIER. THIS WOULD RESULT IN
LOWER SNOW RATIOS SO THAT WHILE WE GET THREE TENTHS OR MORE
PRECIPITATION SNOW RATIOS MAY HOLD US IN THE 2 TO 4 INCH RANGE AS
OPPOSED TO THE 3 TO 6 INCH RANGE THAT MODELS PROGGED. THIS DOESN`T
AFFECT PRECIPITATION CHANCES JUST ACCUMULATIONS. DROPPED ADVISORY
AREA ACCUMULATIONS DOWN ABOUT AN INCH TO ACCOUNT FOR THE LOWER
SNOW RATIOS...BUT THIS STILL KEEPS CURRENT ADVISORIES IN TACT.
ROAD CONDITIONS CONTINUE TO DETERIORATE ACROSS THE AREA. OVER
AREAS EAST OF A MILES CITY TO BROADUS LINE LAW ENFORCEMENT REPORTS
VERY SLICK CONDITIONS BEING COMPOUNDED BY AREAS OF FREEZING FOG.
ADDED MENTION OF FREEZING FOG INTO THE FORECAST FOR THIS AREA.
THIS FOG COULD ADD AN ADDITIONAL LIGHT LAYER OF ICE TO SURFACES.
WINDS HAVE BEEN FAIRLY WESTERLY OVER MOST OF THE AREA THIS
EVENING...BUT WILL VEER MORE NORTHERLY OVER THE NEXT SEVERAL HOURS
AS A REINFORCING COLD SHOT DROPS IN FROM THE NORTH. DESPITE THIS
COLDER AIR EXPECT LOW TEMPERATURES TO HOLD JUST A BIT WARMER THAN
GOING FORECAST AND BUMPED LOWS UP SEVERAL DEGREES WITH CLOUD COVER
AND EXPECTED DEW POINTS. AGAIN NO CHANGES TO THE GOING WINTER
WEATHER ADVISORIES BUT COULD SEE A BIT LOWER ACCUMULATIONS DUE TO
LOWER SNOW RATIOS (SNOWFLAKE SIZE). CHAMBERS

&&

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

MADE A FEW CHANGES TO THE SHORT TERM FORECAST FOR TONIGHT INTO
MONDAY MORNING. OVERALL...AN UNORGANIZED STORM SYSTEM WILL IMPACT
PORTIONS OF THE FORECAST AREA OVER THE COURSE OF THE NEXT 24
HOURS.

THE FREEZING RAIN HAS ENDED ACROSS FALLON AND CARTER COUNTIES.
ALTHOUGH SOME ISOLATED FREEZING DRIZZLE WILL REMAIN
POSSIBLE...WIDESPREAD FREEZING RAIN IS NO LONGER EXPECTED.
THEREFORE...THE FREEZING RAIN ADVISORY HAS JUST BEEN CANCELLED.
HOWEVER...TEMPERATURES WILL REMAIN BELOW FREEZING INTO MONDAY SO
ROADS MAY STILL BE SLICK IN AREAS. AN ORGANIZED TROUGH AND UPPER
LEVEL DISTURBANCE WILL BE OVER THE FORECAST AREA INTO MONDAY
MORNING. HOWEVER...THE BULK OF THE ENERGY WILL BE WELL TO OUR
SOUTH AS AN UPPER LOW MOVES OUT OF COLORADO. WEAK UPSLOPE FLOW
ALONG WITH WEAK VORTICITY WILL AFFECT OUR AREA INTO MONDAY
AFTERNOON. MODELS ARE NOT SHOWING ANY REAL STRONG UPSLOPE FLOW NOR
ANY STRONG LIFT AND DYNAMICS BUT THERE WILL BE ENOUGH ISENTROPIC
LIFT TO KEEP LIGHT TO MODERATE SNOW ACROSS THE SOUTHERN PORTIONS
OF OUR FORECAST AREA. MODELS ARE IN GOOD AGREEMENT IN PLACING THE
HEAVIEST QPF AMOUNTS ACROSS SOUTHERN YELLOWSTONE COUNTY INTO BIG
HORN AND SHERIDAN COUNTIES...AS WELL AS CARBON AND WESTERN POWDER
RIVER COUNTIES. BULK OF THE QPF LOOKS TO OCCUR BETWEEN 0Z AND 6Z
FOR YELLOWSTONE COUNTY AND THEN SPREADING SOUTH THROUGH 15Z FOR
BIG HORN...ROSEBUD...POWDER RIVER AND SHERIDAN COUNTIES. GIVEN
MODEL CONSISTENCIES HAVE DECIDED TO ADD THE RED LODGE
FOOTHILLS...EASTERN CARBON COUNTY AND POWDER RIVER COUNTIES INTO
THE SNOW ADVISORY. AMOUNTS WILL GENERALLY BE IN THE 2-4 INCH RANGE
BUT SOME 5 INCH AMOUNTS WILL BE POSSIBLE FOR THE RED LODGE
AREA...AS WELL AS THE FAVORED UPSLOPE AREAS OF SOUTHERN BIG HORN
COUNTY INTO SHERIDAN COUNTY.

THE SYSTEM QUICKLY SHIFTS SOUTHEAST DURING THE DAY MONDAY
RESULTING IN THE SNOW TAPERING OFF FROM NORTH TO SOUTH DURING THE
MORNING LEAVING ONLY A CHANCE FOR SNOW ACROSS THE MONTANA/WYOMING
BORDER DURING THE AFTERNOON.

A SPLIT FLOW AND STAGNANT AIRMASS WILL THEN BE OVER OUR FORECAST
AREA MONDAY NIGHT AND TUESDAY. THIS WILL KEEP THINGS PRECIP AND
AND WIND-FREE. TEMPERATURES WILL BE BACK TO NORMAL AND SLIGHTLY
BELOW FOR THE FIRST TIME IN AWHILE WITH DAYTIME HIGHS MONDAY AND
TUESDAY IN THE UPPER 20S TO MIDDLE 30S. HOOLEY

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

THE EXTENDED REMAINS RELATIVELY QUIET. CURRENT MODELS RUNS HAVE
NOT INCREASE THE CERTAINTY IN THE FORECAST. FLOW REMAINS
RELATIVELY WEAK...SO MUCH OF THE MODEL SPREAD CAN BE ATTRIBUTED
TO THAT. THE MOUNTAINS WILL SEE A SLIGHT CHANCE FOR SNOW TUESDAY
INTO WEDNESDAY AS A LOBE OF VORTICITY MOVES ACROSS THE STATE. THE
MOUNTAINS WILL SEE ANOTHER SLIGHT CHANCE AS ANOTHER WEAK WAVE MOVES
THROUGH. THERE IS NOT MUCH SUPPORT WITH EITHER OF THESE
SYSTEMS...WITH NO REAL JET ACTIVITY IN THE AREA. OTHERWISE...
TEMPERATURES WILL BE GENERALLY BE AROUND NORMAL TO SLIGHTLY ABOVE.
REIMER
&&

.AVIATION...

LIGHT SNOW SHOWERS ACROSS THE AREA THIS AFTERNOON...WILL INCREASE
LATE THIS AFTERNOON AND EVENING. EXPECT FLIGHT CONDITIONS TO
DETERIORATE TO IFR/LIFR OVERNIGHT AS SNOWFALL INCREASES. WINDS
THIS AFTERNOON WILL REMAIN 15 TO 20 KNOTS OUT OF THE NORTHWEST
FROM BILLINGS EAST...BEFORE DECREASING LATER THIS EVENING. AREA
MOUNTAINS WILL CONTINUE TO BE OBSCURED OVERNIGHT AND INTO
TOMORROW. REIMER
&&

.PRELIMINARY POINT TEMP/POPS...

    MON     TUE     WED     THU     FRI     SAT     SUN
-----------------------------------------------------------
BIL 024/028 014/030 018/035 020/038 021/038 022/039 022/040
    +6/S    11/B    11/B    11/B    11/U    11/B    11/B
LVM 021/032 014/036 022/042 023/040 021/040 022/041 021/040
    +3/S    11/U    11/B    11/B    11/B    11/B    11/B
HDN 022/030 010/031 011/033 012/037 015/037 016/037 015/038
    +6/S    10/B    11/B    11/B    11/U    01/B    11/B
MLS 024/028 012/026 012/029 013/033 017/036 017/034 017/035
    95/S    10/U    11/B    11/B    11/U    01/B    11/B
4BQ 024/030 012/028 013/033 014/037 016/039 016/037 016/038
    +8/S    10/B    11/B    11/B    11/U    01/U    11/B
BHK 022/025 010/025 009/027 012/032 017/037 017/035 016/034
    74/S    10/B    00/B    11/B    11/B    01/U    11/B
SHR 023/031 010/031 014/034 015/037 013/036 015/037 014/038
    +9/S    10/U    11/B    11/B    11/U    01/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY IN EFFECT UNTIL 11 AM MST MONDAY FOR
      ZONES 29>31-34>36-38-39-56>58.
WY...WINTER WEATHER ADVISORY IN EFFECT UNTIL 11 AM MST MONDAY FOR
      ZONES 98-99.

&&

$$
WEATHER.GOV/BILLINGS



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