Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 121607

Area Forecast Discussion
National Weather Service Billings MT
907 AM MST Fri Jan 12 2018

Snow is becoming more scattered as shortwave departs in NW flow
aloft. Upstream there is another wave that will help to enhance
the snow along low level baroclinic zone in our central cwa by
this evening into the overnight hours. Strong lee side surface
ridge will keep east winds and cold air locked up against our
western foothills for most of if not the entire day. Have adjusted
winds and temps and Livingston. Downslope warming in our west
will commence tonight as surface trof begins to slide east behind
aforementioned shortwave.

Will make no changes to current winter highlights yet, to allow
for lingering light snow to diminish further. Travel safe today



.SHORT TERM...valid for Tdy and Sat...

No changes at this time to going highlites. Snow will be tapering
off this morning, but thinking will keep highlites through the
morning commute for light snow and bitter cold wind chills.

Upper level disturbance continues to drop out of Idaho and into
western Wyoming early this morning. Dynamics aloft and low level
over-running of the arctic air at the surface associated with
this feature is creating a broad area of mainly light snow from
the northern Rocky Mountain Front southward across southern
Montana and into northern Wyoming. There are a few bands of
moderate snow embedded in the larger light snow regime at times.
The strongest dynamics are fairly far south and west of our area
and models generally struggle with shallow over-running scenarios
which is leading to NAM and other hi-res models trying to shut off
precipitation across most of the area by sunrise this morning.
The global models and their coarser ensembles continue to produce
light snow off and on through the day as weak isentropic lift and
weak 400-200mb divergence will persist. Both hi-res and global
solutions enhance snowfall over central sections from Harlowton to
Billings to Broadus late afternoon/early evening as another shot
of warm advection arrives with a weak disturbance. Looking like a
narrow band of 1 to 2 inches along this enhanced snowfall line,
with most of the area seeing an inch or less by Saturday morning.

Saturday will see strong warm advection make it to the surface for
most areas with models in good agreement scouring out the arctic
air through the day from west to east. After a day of temps in
the single digits above and below zero today in most areas,
Saturdays highs should push into the 20s and 30s. However, these
scouring out days are always tricky for temperatures as that dense
cold air will hug the river valleys and resist being moved out
resulting in hilltop temperatures getting significantly warmer
than low lying areas. So, there could be some holdouts on the
Saturday warm-up that have to wait until Sunday. For the most part
any accumulating snow will be done for the lower elevations by
mid day Saturday, but some flurries will be possible into Sunday,
especially over SE Montana. Chambers

.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...

Models were in decent agreement with the upcoming pattern until
Wednesday, when the GEFS began to show model spread. The
deterministic GFS and ECMWF also displayed pattern differences
beginning midweek. In addition, the GEFS plumes painted an
uncertain temperature forecast beginning on Monday.

For Sunday, a high amplitude ridge was still forecast to be over
the western U.S.. The forecast area was under the front side of
this ridge with energy forecast to move S through the eastern
zones through early Monday. This energy will push an arctic front
SW into the area on Sunday, along with increasing chances for
snow. The band of snow and front were forecast to push W through
early Monday. So, will have a chance of snow E of KBIL Sun.
afternoon and a good chance over most of the area Sun. evening.
The snow then decreases from E to W late Sun. night. A slight
chance for snow lingers near the mountains Mon. morning. Highs on
Sun. will reach the 20s to the low 40s. Monday temperatures were
challenging and will depend upon the position of the front. Model
blends showed highs from the single digits SE to the upper 30s W.

The upper ridge moves over the area Mon. night through Tuesday
with dry weather. Temperatures will range from the 20s E to the
40s W on Tuesday. Tuesday night remains dry, then a Pacific wave
comes in on Wednesday. As mentioned above, models differed with
this system so have used a blend for the PoPs which were not very
high. Temperatures will be slightly above normal. The remainder of
the period looks unsettled due to Pacific waves. Next chance of
precipitation will be Thursday night and Friday. Above normal
temperatures will continue based on model blends. Arthur



Chances for light snow will decrease through the day. Expect VFR
to MVFR with gradually improving conditions. The chances for snow
increase again tonight with VFR to MVFR conditions. WSW surface
winds will increase late tonight at KLVM, causing areas of blowing
snow. Mountain obscurations will decrease late tonight. Arthur



    Tdy Sat     Sun     Mon     Tue     Wed     Thu
BIL 008 007/037 024/038 008/024 007/033 022/040 024/039
    7/S 61/E    12/O    51/B    00/N    12/O    11/N
LVM 025 025/039 028/042 019/037 019/042 028/041 026/042
    5/S 42/O    11/N    31/B    00/N    11/B    12/O
HDN 006 005/035 021/036 003/023 001/031 017/039 023/040
    7/S 62/S    13/S    60/B    00/U    02/S    11/B
MLS 901 909/024 018/029 910/008 907/022 015/034 019/038
    6/S 23/S    15/S    30/U    00/U    01/B    11/B
4BQ 004 903/032 023/035 904/018 905/029 018/037 021/042
    6/S 33/S    24/S    50/U    00/U    01/B    11/B
BHK 901 914/022 018/028 915/008 915/020 010/033 019/039
    6/S 13/S    25/S    20/U    00/U    00/B    11/B
SHR 014 009/036 026/039 010/028 007/036 021/041 025/041
    6/S 41/B    12/O    61/B    00/U    02/O    11/B


MT...Winter Weather Advisory in effect until 11 PM MST this
      evening FOR ZONES 28>31-34-35-38-40>42-57-58-63.
     Winter Weather Advisory in effect until 11 AM MST this
      morning FOR ZONES 32-33-36-37.
     Winter Storm Warning in effect until 11 PM MST this evening
      FOR ZONES 67-68.


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