Winter Storm in Wyoming, January 31, 2017

Area Forecast Discussion
National Weather Service Billings MT
356 AM MST Tue Jan 31 2017

.SHORT TERM...valid for Tdy and Wed...

Snow is beginning to fill in and expand across the area this
morning as a cold front is working its way into the area from the
north bringing with it colder temperatures and easterly upslope
flow. At the same time, a 150 kt jet is gradually shifting south
over the region bringing upper divergence to the area. Snow will
continue to expand over the area today as Pacific moisture moving
over the region interacts with isentropic lift and convergence
associated with the front. Heaviest snow looks to be during the
day today with lighter snow overnight into Wednesday as the jet
begins to shift south, and along with it better forcing. Snow will
gradually shift south during the day Wednesday and then linger
over the mountains along the Montana/Wyoming border Wednesday
night.

Heaviest snow totals still look to be west of a Roundup to
Ashland line. Latest model runs have increased qpf amounts over
Sheridan County and the Big Horn Mountains. Thus, have increased
snow amounts and issued a Winter Weather Advisory for the Big Horn
Mountains through Wednesday. Otherwise, total snowfall amounts
through Wednesday look to be in good shape from previous forecast
and have left the other winter weather highlites unchanged.
Through Wednesday, 1 to 2 feet can be expected in the western
mountains with totals up to 1 foot in the Big Horns. West of
Billings and north of I-90, 5 to 10 inches can be expected with
lesser amounts around Livingston and the Paradise Valley. 3 to 6
inches with some locally higher amounts still looks good for areas
covered under the Winter Weather Advisory. Some uncertainty
remains in snowfall amounts for the Red Lodge foothills as deeper
upslope flow would allow for more snow to fall, where as a
shallower upslope flow into the Beartooth front would result in
less snow with westerly flow aloft downsloping into Red Lodge.
This will need to be monitored today.

High temperatures will range from the 20s in most places today,
cooling into the teens for Wednesday. STP

.LONG TERM...valid for Thu...Fri...Sat...Sun...Mon...

The trough responsible for Tuesday's snowfall will begin to eject
out of the region by Thursday. As the trough axis swings through
the region another wave of snow will move through Thursday and
last until Friday morning. There is still quite a bit of
uncertainty how far north this band/wave of snow will go, but it
looks like locations south of a Harlowton-Forsyth line stand the
best shot of accumulating snow. The highest amounts will be over
the Beartooths, Big Horns, and associated foothills. Billings
could see another 1 to 3 inches, while locations farther south
and west near the higher terrain could see another 3 to 6 inches,
with locally higher amounts possible.

Behind this trough, larger heights move in and bring quiet weather
for Friday. However, unstable southwest flow with a fetch of
Pacific moisture moves in over the weekend. Pattern recognition
lends high confidence to snow continuing over the mountains
through the weekend. For the Plains, some snow showers could spill
over the higher terrain, but these will be fighting downslope
flow so I just left a slight chance for snow through the weekend.

At the start of next week, a stronger upper level system could
bring another chance for significant snow over the Plains.
However, spread between the models is quite large so just left a
mention of snow in the forecast for next week.

Temperatures will start out cold, and in the teens on Thursday
before warming into the 30s by this weekend. Dobbs

&&

.AVIATION...

Snow will increase through the TAF period as a front moves south
into the region. MVFR conditions will be widespread until the
heavier snow moves in after 12z where IFR/LIFR conditions are
expected at all terminals. The poorest conditions are expected
late this morning. Conditions will improve first at KMLS this
afternoon, and then slowly improve from NE to southwest as the
band of snow shifts south later tonight. Widespread mountain
obscurations are expected through the entire TAF period. Dobbs

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Wed     Thu     Fri     Sat     Sun     Mon
-------------------------------------------------------
BIL 026 011/016 005/013 901/026 016/034 021/039 019/030
    +/S 84/S    45/S    51/B    22/J    22/J    22/J
LVM 030 008/015 003/014 000/034 026/043 030/045 026/038
    +/S 85/S    47/S    52/S    23/W    22/W    33/W
HDN 027 007/016 000/015 905/025 010/030 013/038 014/029
    +/S 74/S    34/S    50/B    22/J    22/J    22/J
MLS 026 008/015 000/013 903/020 010/025 010/028 013/026
    3/S 21/B    11/B    10/B    12/J    12/J    22/J
4BQ 028 006/016 902/014 905/025 014/030 012/035 013/030
    6/S 32/S    23/S    40/B    11/E    11/E    12/J
BHK 024 006/012 904/010 904/019 010/024 007/025 011/025
    3/S 11/B    11/B    10/U    11/E    11/E    22/J
SHR 027 008/015 901/013 902/028 017/036 017/040 016/033
    9/S 86/S    65/S    40/B    12/J    11/B    12/J

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect until 6 AM MST Wednesday FOR
      ZONES 28-34-40>42-63-66.
     Winter Weather Advisory in effect until 6 AM MST Wednesday
      FOR ZONES 29-35-38-39-56>58-64-65.
     Winter Storm Warning in effect until 6 PM MST Wednesday FOR
      ZONES 67-68.
WY...Winter Weather Advisory in effect until 6 AM MST Wednesday
      FOR ZONE 99.
     Winter Weather Advisory in effect until 6 PM MST Wednesday
      FOR ZONE 98.

&&

weather.gov/billings