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Area forecast discussion 
National Weather Service Billings Montana
325 am MST Sat Dec 3 2016

Short term...valid for tdy and sun...

Active period of weather ahead. Weather pattern will lose
seasonality to end the weekend with the introduction of an Arctic
cold front Sunday night. The Arctic cold front will mostly impact
the long term period, but affects in falling temperatures and
accumulating snow will be felt as early as Sunday night for the
plains. The mountains will get a healthy shot of snowfall from
Sunday through Monday. Finally, strong winds from Livingston to
Nye will cause travel concerns through early Sunday.

Winds have already gusted to 54 mph at Livingston. Surface
pressure gradient from Idaho Falls to Lewistown was 14mb. Forecast
models take that gradient up to around 15mb this morning. Strong
surface pressure falls were still occuring over southern Canada,
so feel confident advisory criteria will be hit this morning at
Livingston. Gradient relaxes this afternoon as the surface trough
moves off the slopes and advances into eastern Montana. Surface
pressures lower once again tonight in response to additional
energy sliding into southern British Columbia. This should crank
the winds up again and hold them into Sunday morning.

Shortwave energy was sliding across the forecast hour this hour
and generating a few snow showers. Downslope flow was drying out a
great deal of this activity, but enough there to warrant a low
pop. This wave shifts east this afternoon. Should be fairly quite
until late tonight and Sunday when the mid level flow backs and
taps into deeper Pacific moisture. The Southwest Mountains will
start to pick up snow in earnest Sunday and continue this trend
into Monday. The GFS has the heaviest qpf over Yellowstone Park at
this time, but enough mid level instability to provide decent snow
rates. Lapse rates 700-500mb were around 7.5-8c/km Sunday into
Monday. The moisture feed diminishes for the mountains Monday
evening. Have decided to issue a Winter Storm Watch for the
Southwest Mountains for Sunday through Monday.

For the plains, temperatures will remain seasonal today and again
Sunday. An Arctic cold front will push in from the north Sunday
night. Strong shortwave energy will drive into western Montana and
northern Idaho and generate lift as the front advances southward.
Would expect a mix of rain and snow showers Sunday evening to
quickly change over to all snow Sunday night as 850mb temperatures
fall to -6c by 12z Monday. This could lead to some slick roads
Sunday night with roads freezing as the Arctic plunges in. Models
have been all over the place with snow potential for the plains
and have not come into total agreement yet, so confidence not high
on snow amounts for the lower elevations. Snow will continue into
Monday. The stage is certainly set for much colder temperatures
this week. Twh

Long term...valid for Mon...Tue...Wed...Thu...Fri...

Monday morning shortwave trough axis will be over the middle of
the state as surface front slides in with associated bands of
snow. Absaroka Range will see the brunt of the higher snow
accumulations with somewhere around a foot expected by Monday. As
front slides eastward through the state, Arctic air mass moves in
from the northwest bringing bitter cold to the region. Expect
light snow through the day Monday with cold northwest flow and
falling temperatures. Accumulations of 2 to 4 inches expected in
most low-land locations with 6 to 8 inches in the bighorns through
Monday.

Cold air mass really begins to filter in by Tuesday morning as
850 temps below -20 c slide into the region beneath the upper-low.
Kept high temps in the single digits or lower with below/near zero
lows through Thursday morning, which is consistent with previous
forecasts.

Winds will remain elevated over the eastern plains Tuesday and
Wednesday. Wind chills will certainly be a concern as 15 to 20 mph
winds will allow for periods of wind chills below -30 f.

Thursday should mark The Retreat of the Arctic air mass.
Temperature forecast remains uncertain as the models disagree on
when the downslope begins over the foothills. For now kept teens
to 20s in for the highs with winds beginning to switch
southwesterly over the foothills Tuesday afternoon.

Friday and Saturday temps continue to trend upward as the next
system approaches from the northwest. Keeping an eye on the winds
through The Gap areas with this system on Saturday morning. GFS
has Lee side troughing developing with winds 40 to 50 mph from
Livingston to Big Timber, however still a ton of uncertainty at
this point. Walsh

&&

Aviation...

VFR conditions will prevail through the morning with vcsh for all
the terminals. Brief periods of MVFR ceilings and visible due to these
showers is possible. Southwest winds gusting to 45 kts ongoing at
lvm which will persist through the period. A band of clouds and
light rain/snow will move through mls after 15z, expect a few
hours of MVFR/IFR ceilings associated with this band. Walsh

&&

Preliminary point temp/pops...

Tdy sun Mon Tue Wed Thu Fri
-------------------------------------------------------
bil 044 028/043 021/025 005/008 905/004 903/019 011/032
2/j 23/west 76/j 32/j 21/b 11/b 12/j
lvm 041 031/041 020/023 001/009 907/009 901/023 017/037
2/west 45/west 85/j 32/j 21/b 11/b 22/j
hdn 044 027/045 022/027 005/009 905/003 907/019 007/029
3/west 22/west 66/j 32/j 21/b 11/b 11/east
mls 042 024/042 020/026 003/007 907/003 906/012 000/023
3/west 12/west 56/j 32/j 11/b 11/b 11/east
4bq 041 023/041 020/027 002/008 908/003 908/016 000/029
2/west 21/east 57/j 32/j 11/b 11/b 11/b
bhk 039 021/039 018/025 002/006 908/002 908/012 905/016
2/west 10/b 46/j 32/j 11/north 11/b 11/east
shr 042 020/043 021/026 002/010 907/007 910/021 005/034
2/west 22/west 67/j 32/j 21/b 11/b 11/b

&&

Byz watches/warnings/advisories...
Montana...Wind Advisory in effect until 6 PM MST Sunday for zones
65-66.
Winter Storm Watch in effect from Sunday morning through
Monday afternoon for zone 67.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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