Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 082357
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
455 PM MST Thu Dec 8 2016

AVIATION SECTION UPDATED

.DISCUSSION...

Tonight through Saturday...Cold surface high pressure remains
entrenched across the area today under a broad upper level trough
which is shifting into the eastern half of the continent.
Upstream, a series of Pacific jet and shortwave impulses are
moving onto the west coast with an area of light snow on the nose
of this plume of moisture extending from SW WA through Southern ID
this afternoon. The initial wave of Pacific moisture and
shortwave energy will weaken considerably as it moves ENE
tonight. Light snow will develop this evening over SW MT and
spread NE late tonight through Friday morning before diminishing
Friday afternoon as the energy passes. Still looking for around
1-3 inches of snow accumulation tonight for areas S of I90, with
generally less than an inch across areas to the north. Winter Wx
Advisory remains in place beginning this evening for
Madison/Gallatin/Beaverhead counties with local accumulations
closer to 4 inches possible from Monida Pass to West Yellowstone
along the ID border. Second wave of moisture and upper jet energy
pushes into the region Friday night spreading a more widespread
light snowfall across the much of the forecast area. Liquid
equivalent precip amounts are fairly low but with good snow to
Liquid ratios expected, most areas should see an additional 1 to
3 inches. Winter weather advisory for SW/Central MT begins Friday
evening to highlight this event with snow ending from W to E on
Saturday as the system exits. Winds look to remain fairly light
through both of these periods of light snow. Just some slight
moderation in the much below average temperatures is expected
through Saturday due to the influx of moisture. Hoenisch

Saturday Night through Wednesday...Flow aloft across Central and
Southwest Montana will generally be from the west Saturday night but
a shortwave moving through the flow will bring increased chances of
precipitation to the region by Sunday. The passage of the shortwave
will bring an associated cold front across the Canadian border by
late Sunday, and temperatures will take a downward direction again.
Another disturbance will move into the area Monday and this will
keep cold air across northern portions of the region. Snow will be
moving out of the area by Tuesday but the cold air already in place
will result in continued cold temperatures. High pressure will build
over the zones and the air mass will dry until another shortwave
brings snow across the Rockies again late Wednesday night and
Thursday. The surface boundary between cold air north and warmer
south will likely be lying across Southwest Montana and this area
would be expected to receive the most snow.
Zelzer

&&

.AVIATION...Updated 2355Z.

Mix of VFR/MVFR conditions expected across central and southwest MT
this evening as broad plume of Pacific moisture and a weak upper-
level trough move into the region. Localized bands of very light
snow, mainly from KGTF south to KHLN/KBTM, will occur over next hour
or two, but not present much impact other than briefly lower
ceilings. Primary period of snow will start over southwest MT around
03-06Z and then gradually spread north overnight and into Fri
morning. MVFR/IFR conditions will become more widespread as the
precipitation comes into central MT, but conditions will see steady
improvement starting around 18Z tomorrow near KEKS/KBZN and then
progress toward KHLN/KGTF later in the aftn.  Surface winds
remaining generally less than 10 kts across the region through
tonight and tomorrow.
Waranauskas

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  -9   2   0  14 /  50  70  80  40
CTB -13  -3  -7   4 /  30  50  60  40
HLN  -3  17  13  30 /  70  70  80  30
BZN   3  25  20  32 /  70  50  80  40
WEY   6  26  17  28 /  90  80  80  70
DLN   8  32  21  32 /  90  40  60  30
HVR  -9   2  -3   2 /  10  20  70  60
LWT  -6   6   0  14 /  30  60  80  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 PM Friday to 5 PM MST Saturday
Broadwater...Cascade...Central and Southern Lewis and Clark...
Fergus...Jefferson...Judith Basin...Meagher.

Winter Weather Advisory until 5 PM MST Saturday Beaverhead...
Gallatin...Madison.

&&

$$

weather.gov/greatfalls


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