Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 180545

Area Forecast Discussion
National Weather Service Great Falls MT
1045 PM MST Fri Nov 17 2017

Updated Aviation Discussion


Main updates this evening were to increase the snow/blowing snow
along the Continental Divide south into Jefferson County to
reflect the persistent snow and strong wind gusts there. Have been
addressing this with Special Weather Statements, and will keep an
eye on it for a possible Winter Weather Advisory. Gusts of 40 to
50 mph have been common through favored passes, including Marias
Pass and MacDonald Pass. The Montana Department of Transportation
even has an alert for Severe Driving Conditions from Marias Pass
to near Browning. Overall, am expecting the snow and winds along
the Divide to decrease somewhat overnight to at least lessen the
impacts from blowing snow. Again, will monitor the situation.
Remainder of the forecast appears to be on track.



Drier conditions move into the region this weekend with
temperatures near average through Saturday. Temperatures trend
warmer with increasing winds Sunday.


Updated 0545Z.

Upper level ridge of high pressure building east into the Northern
Rockies and MT tonight will spread drier and more stable air into
the region with any lingering snow showers along the continental
divide diminishing by Saturday morning. VFR conditions will prevail
at area terminals with scattered to broken mid level cloud cover
over SW MT gradually diminishing late tonight through Saturday
morning. Gusty surface winds will continue along the Rocky Mtn front
tonight and increase at all area terminals Saturday afternoon.


/ISSUED 445 PM MST Fri Nov 17 2017/

Tonight through Sunday...Model analyses and water vapor satellite
reveal a synoptic trough axis is now moving east of our forecast
area. Weak instability persists due to cooling aloft. However,
any remaining rain or snow showers are expected to clear this
evening as pressure rises at the surface and aloft. Single digit
temperatures are expected tonight in southwest valleys under
clearing skies. Breezy conditions continue tonight across much of
North central Montana with a strong pressure gradient persisting
over the region. The mid-level westerly flow increases on Saturday
for windy conditions across the north-central MT plains, then
increases further by late Sunday as the upper level ridge de-
amplifies. The lee-side trough of low pressure deepens further
Sunday as well, for increasing potential of strong winds,
initially along the Rocky Mtn Front, and possibly extending east
into adjacent western portions of north-central MT by late Sunday.
A High Wind Watch has been posted to cover this potential hazard.

Sunday night through Friday...A progressive pattern is still
expected during this period. High pressure ridging aloft looks to
exit the CWA to the east Sunday night and be followed by the passage
of a shortwave trough and Canadian cold front Monday. High pressure
ridging aloft should then become re-established over the region
Tuesday through Wednesday. However, multiple and subtle weather
disturbances may traverse the ridge during this period. This ridge
may then be broken-down by a shortwave trough and Pacific cold
frontal passage on Thanksgiving. Another high pressure ridge aloft
should then build-in from the west on Friday, but model guidance
differs on how quickly this will happen. During this progressive
pattern, atmospheric profiles look to be favorable for periods of
strong, gusty downslope winds. This may especially be the case along
the Rocky Mountain Front and during Sunday night, as well as

The aforementioned pattern will be conducive to periods of upslope
precipitation, mainly in the form of snow, along the Continental
Divide and the Southwest MT mountains. Elsewhere, the best potential
for precipitation looks to be on Monday, courtesy of the Canadian
cold frontal passage, and on Thanksgiving into Friday, along and
behind the aforementioned Pacific cold front. Overall, high and low
temperatures will tend to be near or above-normal during the period.
However, some slightly below-normal readings are possible Monday and
Friday, courtesy of the previously-mentioned cold frontal passages.


GTF  29  41  31  48 /   0   0   0   0
CTB  23  38  26  44 /   0   0   0   0
HLN  22  40  21  43 /  10   0   0   0
BZN  15  35  15  39 /  10   0   0   0
WEY   5  27   7  30 /  20  10  10   0
DLN  16  34  17  39 /   0   0   0   0
HVR  18  39  23  46 /   0   0   0   0
LWT  23  39  25  46 /   0   0   0   0


High Wind Watch from Sunday morning through late Sunday night
Cascade...Central and Southern Lewis and Clark...Eastern
Pondera...Eastern Teton...Judith Basin...Toole.

High Wind Watch from late Saturday night through late Sunday
night Eastern Glacier...Northern Rocky Mountain Front...Southern
Rocky Mountain Front.


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