Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 181702
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
1002 AM MST Mon Dec 18 2017

.UPDATE...

Very strong winds continue across the western foothills this
morning with gusts in excess of 70 mph at times at Livingston.
Strong winds will continue through the day, gradually decreasing
during the late afternoon and evening as an approaching cold front
helps the surface pressure gradients relax a bit. Will continue
the High Wind Warnings in effect until 6pm. Cold front is still
expected to drop south through the area this evening with some
light rain/snow associated with it. Not expecting much in the way
of snow accumulations, except in the southwest mountains where
snow showers can be expected through the day with a couple inches
of snow possible on south and west facing slopes. Have adjusted
pops and winds to current trends. Otherwise, the rest of the
forecast remains on track and the previous forecast discussion and
an updated aviation discussion are below. STP

&&

.SHORT TERM...valid for Tdy and Tue...

Very strong winds have been occuring overnight for the Livingston
area and adjacent foothills. Strong surface low pressure across
southern Canada combined with high pressure over southern Idaho
has provided for a very windy setup across the Upper Yellowstone
and Stillwater Valleys. Livingston airport has gusted to 81 mph
with several 75-80mph gusts that past few hours. Latest model
guidance and local wind guidance show these strong winds
continuing through this morning and not peaking until about noon.
Big Timber continues to gust around 58 mph a few times as well.
High Wind Warnings for these locations will continue through this
afternoon. In addition, models bring a 700mb westerly flow at
65-70kts across Wheatland County this morning. A surface trough
will move east of the area today, and this combined with some pre-
frontal mixing may allow these winds to mix down to the surface
today. Currently winds have been gusting to around 40 mph at
Harlowton but we will continue with the high wind warning for that
area as well.

A cold front will drop south across the forecast area this
evening and overnight which will decrease pressure gradients and
allow the very strong winds for Livingston and Nye to end. The
front has some moisture with and behind it so we will have a
slight chance for some light snow across the forecast area tonight
into the day Tuesday. Pressure gradients will tighten once again
across the Upper Yellowstone and Stillwater Valleys Tuesday night.
This will bring another period of strong winds to the Livingston
and Nye areas. However, gradients do not look as strong as current
gradients but will mostly likely need an wind advisory for
Tuesday night. Hooley

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

First arctic shot of the season expected on Wednesday as 850mb
temps around 7C above zero plunge to -14C behind a fast moving
cold front. Splitting disturbance tracks over the area while the
front passes through providing some lift so have a quick shot of
a couple of inches of snow for lower elevations with higher
amounts towards the foothills. Think most of the precipitation
will fall as snow with temperatures falling sharply through the
afternoon. Biggest threat is the roads will be warm with moisture
melting and becoming ice making miserable travel and having that
layer get stuck on the roads beneath any additional snowfall.

Snow should end Wednesday night with the first shot of cold
settling into the area for Thursday with high temperatures 20
degrees lower than Wednesday. However...the next approaching cold
front moving through Alberta induces some leeside troughing and
pushes the coldest air eastward which generates an isallobaric
wind which could bring a period of blowing snow for much of the
area...depending on how much snow falls.

Next cold front arrives Thursday night with a chance for
additional snow and it brings even colder air. ECWMF and GFS
showing differences in how much lift will come with the front as
the ECMWF hints at some confluent midlevel flow along the frontal
passage which may delay the better snowfall until upslope
influences develop putting the better chance of snow on Friday.

Both models indicate the area will be locked into much colder air
for the foreseeable future from the weekend and beyond. One
subtle difference is the GFS drives a clipper through the Dakotas
on Sunday with reinforcement of colder air but does bring a period
of klondike chinooking while the ECMWF actually just keeps deeper
colder air in place. Beginning of next week looks like many areas
could see temperatures around zero at best for highs with
negative teen lows a possibility...if not colder. borsum

&&

.AVIATION...

Very strong southwest winds will gust to 50-65kts from Big Timber
to Livingston through midday. Decreasing winds during the
afternoon. Expect VFR conditions except where the high winds are
lowering visibilities. A weak cold front moves through the area
during the afternoon with increasing shower activity and
obscurations over the mountains. Areas north of a line from 3HT to
RPX to MLS could see some light snow as well. borsum/Reimer

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 048 028/041 032/040 011/025 016/023 005/014 002/018
    1/N 32/S    15/O    62/S    35/S    42/S    11/B
LVM 048 037/046 037/041 012/026 017/022 003/012 001/016
    1/N 32/O    16/O    51/Q    46/S    43/S    11/N
HDN 050 027/044 027/046 012/025 015/023 006/016 002/019
    1/N 32/S    15/O    62/S    35/S    43/S    22/S
MLS 049 025/038 024/041 010/021 013/021 005/014 001/017
    2/W 42/O    23/O    52/S    24/S    32/S    21/B
4BQ 052 026/043 027/048 010/024 011/023 004/015 001/017
    1/N 21/E    11/E    63/S    14/S    32/S    21/B
BHK 048 022/036 020/038 007/018 009/018 002/011 902/012
    2/W 41/E    22/S    52/S    13/S    22/S    11/B
SHR 050 026/044 026/049 011/025 010/023 003/014 901/018
    1/B 11/B    13/O    73/S    25/S    43/S    22/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Warning in effect until 6 PM MST this evening FOR
      ZONES 28-41-65-66.
WY...None.

&&

$$
weather.gov/billings



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