Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 200245

Area Forecast Discussion
National Weather Service Glasgow MT
745 PM MST Sat Jan 19 2019


Update: A stationary front is near Zortman and Winnett this
evening. Meanwhile, a shortwave in NW flow aloft is moving from SW
Saskatchewan through the NE corner of Montana this evening and
bring some snow to the NE part of the forecast area. The wave will
move to the east after midnight tonight. Updates included are to
adjust temperatures overnight as some locations have reached their
forecasted lows, to adjust pops and winds this evening.

Previous short term:
The main story for the forecast is as such: Predominant flow
pattern aloft will be northwesterly across the region through the
forecast period, with a single large trough expected to push
through the region late Sunday through early Tuesday. Coincident
with this trough passage will be the best chance for accumulating
snowfall for the period.

Short-term: Chinook downslope pattern to the west will bring
potentially large T differences from West to East across the
region this afternoon, depending on how far the effect can reach
with the current snowpack across the northeast. Light snowfall in
the far northeast will follow along a NW/SE oriented vorticity
band through tonight, though accumulations should remain under 1".

Tomorrow, the NW flow pattern breaks down as a deep trough aloft
pushes through the region. There will be enough synoptic energy to
initiate the larger scale precipitation system. Down at the
mesoscale, the surface front, and attendant moisture profile will
determine the axis of greatest snowfall. Models are showing that
this axis is expected to line up from the Little Rockies through
Ft Peck Lake. Some rain in the Missouri River Breaks region will
limit snowfall accumulations, and could lead to some mixed
precipitation in that area as well. A winter weather advisory was
deemed necessary for much of the western zones where 2-4" of
accumulation was likely. A small enough corner of SW Valley County
met that criteria to where it was felt that S Valley could be left
off for now. Total accumulations across the advisory area are
expected to be 2-3" with up to 5" expected potentially at
Zortman. The rest of the region should expect at least a trace of
snowfall, up to 2" outside of the advisory area.

Long-term: Once the Sunday-Monday system departs the region for
the northern plains, northeast Montana will return to a fairly
static northwest flow pattern as a ridge develops along the West
Coast and then subsequently gets blocked from translating to the
east, leaving a static upper-level flow pattern likely for the
region through the rest of the forecast period. The weather
conditions thus should be fairly consistent as well, with lows
expected in the single digits either side of zero to the teens
above zero, and highs mostly in the 20s. Precipitation chances are
expected to be low, though if some stray pieces of upper-level
energy are able to push through the flow pattern over the region,
some light precipitation may be possible. Confidence is moderate
in that at best at this time.




Expected Flight Conditions: VFR-MVFR

Synopsis: Generally dry conditions with a cloud deck of mainly
mid- to high-level clouds coming off the Rockies will dominate the
weather through tomorrow afternoon across the region. However,
a small disturbance may bring some light vicinity precipitation to
OLF and SDY tonight, and with that the potential for some short-
term drops in ceilings to MVFR levels. A more organized winter
storm system is expected to push through tomorrow night into
Monday morning.

Winds: Afternoon winds will be out of the southeast at 5-15 kts
and then relax to light and variable through much of tomorrow.



Winter Weather Advisory from 6 PM Sunday to 6 AM MST Monday for
Central and Southeast Phillips...Garfield...Petroleum...
Southwest Phillips.


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