Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 171120

Area Forecast Discussion
National Weather Service Great Falls MT
420 AM MST Mon Dec 17 2018

Updated Aviation Discussion


A weakening Pacific weather system moves into the Northern Rockies
and Montana this afternoon and evening for increasing cloud-cover
with light precipitation mainly confined to the mountains of western
and southwest Montana. A stronger storm system moves across the
region Tuesday through early Wednesday, bringing strong winds to
central portions of Montana as well as heavy snow to the mountains
of western Montana.



Today through Wednesday...Northern portion of a split upper
level trough moving inland along the west coast this morning will
progress east across MT tonight while weakening. This will bring
increasing cloud-cover through today while temperatures remain
well above seasonal averages. Meanwhile, A strong Pacific upper
level jet and atmospheric river of moisture continues to drive
eastward, expected to reach the WA/OR coast tonight then push
inland Tuesday and Tuesday night. Strong mid level flow aloft
begins to spread into the region early Tuesday with impactful
winds initially developing along areas immediately east of the
Rocky Mtn Front early Tuesday morning. Strong winds appear likely
to spread east and southeast into central MT through the day
Tuesday as strong mid-level flow aloft overspreads the region with
the arrival of initial shortwave and surface Pacific front/trough
and have issued a high wind watch where confidence is greatest
through Tuesday afternoon. After the initial shortwave energy and
surface front cross the region late Tuesday afternoon/evening flow
aloft remains quite strong into at least Wednesday morning. High
wind highlights may need to be expanded farther east and south for
the Tuesday night period as the front progresses through far
eastern and SE portions of the forecast area. Precipitation will
develop Tuesday morning along the continental divide west of the
Rocky Mtn Front and continue through Wednesday morning before
diminishing. Heaviest snow accumulations will be limited to areas
above 5000 feet near the continental divide with main impact area
being Marias Pass on highway-2 during this period. Several inches
of snow are expected at Marias pass with much heavier amounts
across the highest elevations of Glacier National Park and back-
country areas of the Rocky Mtn Front, where a Winter storm watch
has been issued for elevations above 5000 ft. Hoenisch

Another period of upper level ridging shifts across the region late
Wednesday through Thursday before the next Pacific system moves
onshore and across the Northern Rockies and MT Friday. Models are
having some difficulty yet with the timing and specifics of this
energy which is typical in fast flow aloft. Another period of strong
winds and at least some mountain snowfall is likely with this
system. Temperatures remain well above seasonal averages through
Thursday before cooling as the the next series of weather systems
arrive late this week into the weekend.


Updated 1200Z.

VFR conditions prevail at most terminals through tonight. Higher
level cloud-cover increases today as a weakening Pacific weather
disturbance moves into the northern Rockies today and across the
rest of MT tonight. Precipitation should be confined to areas
near the continental divide where some mountain obscuration is
possible. Surface winds will remain breezy across western portions
of north-central MT with southerly winds increasing tonight before
strong winds develop Tuesday. Hoenisch


GTF  50  35  54  37 /   0   0   0  10
CTB  48  32  51  35 /  10  10  10  10
HLN  44  26  47  32 /  10   0  20  40
BZN  42  21  43  27 /  10  10  20  40
WEY  36  16  29  17 /  20  50  60  90
DLN  44  21  39  25 /  10   0  20  50
HVR  48  29  52  35 /   0   0   0  10
LWT  51  30  50  33 /  10  10   0  10


High Wind Watch from Tuesday morning through Wednesday afternoon
Broadwater...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Jefferson...Judith Basin...Liberty...Meagher...Toole.

Winter Storm Watch from Tuesday morning through Wednesday
morning above 5000 feet for Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

High Wind Watch from late tonight through Wednesday afternoon
Northern Rocky Mountain Front...Southern Rocky Mountain Front.


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