Area Forecast Discussion
Issued by NWS Billings, MT

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000
FXUS65 KBYZ 312226
AFDBYZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
326 PM MST SAT JAN 31 2015

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

SNOW THROUGH THIS EVENING IS THE MAIN SHORT TERM FORECAST CONCERN
AS ROADS WILL BE SLIPPERY IN PLACES...ESPECIALLY AFTER SUNSET.

SNOW RAPIDLY FILLED IN AND INTENSIFIED OVER MUCH OF SOUTHERN MT
EARLY THIS AFTERNOON AS THE PEAK OF THE FORCING TIED TO THE MID-
AND UPPER-LEVEL SHORTWAVE TROUGH BEGAN TO CROSS THE AREA. WE FEEL
THE SNOW WILL WIND DOWN DURING THE EVENING AS THAT FORCING EXITS
STAGE RIGHT INTO THE DAKOTAS...BUT RECENT HIGH-RESOLUTION MODEL
GUIDANCE AND THE COARSER 12 UTC GFS AND TO A LESSER EXTENT THE
ECMWF STILL SUPPORT EVENT TOTALS OF 1 TO 2 INCHES IN MANY SPOTS BY
EVENING. WE WERE SOMEWHAT CONCERNED ABOUT HIGHER-THAN-EXPECTED
SNOW TOTALS IN AND NEAR BILLINGS GIVEN RADAR TRENDS THROUGH 2130
UTC...WHICH HAD AN OROGRAPHIC SNOW BAND FROM LAVINA TO BROADVIEW
AND DOWNSTREAM TO THE METRO AREA. A MORE CONTEMPORARY TREND IN
RADAR DATA IS FOR THAT BAND TO DIMINISH THOUGH...WHICH IS A TREND
SUPPORTED BY THE DEPARTURE OF LARGER-SCALE FORCING ALOFT. WE HAVE
THUS STAYED THE COURSE WITH THE IDEA THAT TOTAL SNOW ACCUMULATION
IN BILLINGS WILL BE AN INCH OR LESS. AFTERNOON RADAR IMAGERY ALSO
ALSO SUPPORTED TODAY/S HRRR AND HIGH-RESOLUTION WRF-NMM AND WRF-
ARW RUNS FOR A MODEST UPSLOPE-AIDED ENHANCEMENT OF SNOW IN THE
RED LODGE FOOTHILLS WHERE WE ARE NOW CALLING FOR 2 TO 3 INCHES OF
SNOW THROUGH THIS EVENING.

DESPITE RELATIVELY LOW SNOW AMOUNTS PRECLUDING US FROM ISSUING ANY
HEADLINES FOR THIS EVENT...ROADS WILL BECOME SLIPPERY BY EVENING
IN AREAS WHERE THEY AREN/T ALREADY AS THE LACK OF SOLAR RADIATION
AFTER SUNSET WILL ALLOW ROAD SURFACES TO DROP BELOW FREEZING AND
ANY MOISTURE ON THEM TO FREEZE. THAT IS OUR MAIN FORECAST MESSAGE.

BY SUNDAY...FLOW ALOFT TURNS ANTICYCLONIC WHILE SHORTWAVE RIDGING
MOVES OVERHEAD AND THAT WILL LEAD TO A DRY DAY WITH HIGHS POSSIBLY
HELD A BIT LOWER THAN THEY WOULD BE OTHERWISE BY FRESH SNOW COVER.
THE 12 UTC MODEL SUITE REMAINED CONSISTENT IN SHOWING A WARM FRONT
MOVING EASTWARD ACROSS THE REGION SUNDAY NIGHT INTO MONDAY AND WE
ARE CARRYING SOME POPS IN THE FORECAST WITH THAT FEATURE...THOUGH
FORCING LOOKS WEAK AND WILL LIKELY BE GREATEST IN SOUTHEASTERN MT
TO THE EAST OF BILLINGS ON MONDAY MORNING WHERE WARM AIR ADVECTION
ALOFT WILL BE FOCUSED.

HIGHS MONDAY WILL JUMP BACK UP WELL INTO THE 40S F ON THE WARM
SIDE OF THAT FRONT IN SOUTH CENTRAL MT AND NORTH CENTRAL WY. ITS
PLACEMENT IS UNCLEAR THOUGH...AND BECOMES EVEN MORE UNCERTAIN COME
MONDAY NIGHT WHEN IT IS LIKELY TO WAFFLE BACK SOUTHWARD AGAIN /AT
LEAST BY THE 12 UTC GFS AND ECMWF...NOT THE NAM/. WE USED A BLEND
OF CONTINUITY AND THE FORMER TWO MODELS TO LEAVE SOME HIGH-CHANCE
TO LOW-END LIKELY POPS IN THE FORECAST BY LATE MONDAY NIGHT ACROSS
PARTS OF THE AREA SINCE THE FRONTAL ZONE COULD FAVOR PRODUCTION OF
SOME LIGHT SNOW. SCHULTZ

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

DID MAKE SOME CHANGES TO THE EXTENDED FORECAST...AND THE
CONCENTRATION OF THESE WERE IN THE EARLIER PART OF THE PERIOD.
NORTHWEST FLOW IS PROGGED OVER THE AREA...WITH A STRONG SHORTWAVE
ROTATING INTO NORTH DAKOTA TUESDAY AND TUESDAY NIGHT. THIS WILL
PUSH A REINFORCING SHOT OF COLD AIR INTO THE AREA. MODELS HAVE
BACKED OFF SOME ON THE DEPTH OF THE COLD AIR AND THUS GUIDANCE WAS
WARMER. THE BULK OF THE COLDER AIR WAS SHOVED TO THE EAST. BUMPED
TEMPERATURES UP A BIT BASED ON BASED ON MODEL TRENDS FOR TUESDAY
AND MAINTAINED ON WEDNESDAY.

MODELS WERE DIFFERENT ON QPF SOLUTIONS AS THE GFS WAS WETTER
EARLIER THAN THE ECMWF AND THE ECMWF HOLDING ONTO PRECIPITATION
LONGER INTO WEDNESDAY. BUMPED POPS FOR TUESDAY AS LOOKS GOOD FOR
AN OVERRUNNING EVENT MONDAY NIGHT INTO TUESDAY NIGHT WITH A DECENT
BAROCLINIC ZONE INVOLVED AND SOME PACIFIC MOISTURE AVAILABLE.
SHOULD THE ECMWF VERIFY...MAY HAVE TO RAISE POPS INTO WEDNESDAY
AND THURSDAY WITH PERSISTENT MID LEVEL WARM ADVECTION. LEFT THE
REST OF THE FORECAST IN TACT AS AN UPPER RIDGE BUILDS IN FOR THE
END OF THE WEEK WITH WEAK ENERGY RIDING OVER THE TOP. WINDS COULD
BECOME STRONG AT LIVINGSTON AND NYE THURSDAY AND THURSDAY NIGHT AS
ENERGY FLATTENS THE RIDGE. TWH
&&

.AVIATION...

AREAS OF LIGHT SNOW WITH POCKETS OF MODERATE SNOW WILL CONTINUE
ACROSS MOST OF THE AREA THIS AFTERNOON. THE HEAVIER SNOW SHOWERS
WILL LOWER CONDITIONS TO IFR AND LIFR. THE SNOW WILL TAPER OFF
THIS EVENING...WITH THE SNOW TAPERING OFF SLOWER OVER SOUTHEAST
MONTANA AND ALONG THE EAST SLOPES. CONDITIONS WILL IMPROVE TO VFR
OVERNIGHT. MOUNTAINS WILL BE OBSCURED. TWH

&&

.PRELIMINARY POINT TEMP/POPS...

    SUN     MON     TUE     WED     THU     FRI     SAT
-----------------------------------------------------------
BIL 014/031 029/046 028/030 015/033 026/045 036/053 038/056
    60/B    21/E    55/J    52/J    21/B    01/N    11/N
LVM 016/040 031/049 035/035 021/039 029/049 036/054 039/055
    40/B    31/N    44/W    43/W    21/E    11/N    21/N
HDN 012/030 023/043 024/028 008/032 018/043 030/051 030/054
    80/B    22/S    55/J    42/J    21/B    01/B    11/B
MLS 007/023 020/034 018/019 000/023 012/038 025/046 027/052
    91/B    24/O    65/J    20/B    11/B    11/B    12/W
4BQ 009/027 022/043 025/026 007/030 019/044 029/054 034/058
    +1/B    23/O    54/J    31/B    11/B    01/B    12/W
BHK 005/018 013/032 016/016 000/020 012/036 025/045 028/050
    +1/B    24/S    54/J    20/B    10/B    11/B    12/W
SHR 012/028 021/046 025/027 013/032 020/044 029/055 031/055
    61/B    21/E    22/J    52/J    11/B    00/B    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
WY...NONE.

&&

$$
WEATHER.GOV/BILLINGS


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