Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 230400

Area Forecast Discussion
National Weather Service Great Falls MT
957 PM MDT Sun Oct 22 2017


957 pm additional update...Winds continue to decrease over the
previously warned area, so have allowed it to expire. Only other
adjustment was to decrease the chance for showers over the area
around Great Falls. Convective showers continue over the mountains
to the west, which may still cause an isolated shower to move over
the area, but the likelihood that this will happen is less than
previously thought.

Main update this evening was to cancel the High Wind Warning for
areas west and south of Liberty, Chouteau, and Judith Basin
Counties. Winds have decreased dramatically early this evening
with the loss of daytime heating and the exit of the cold front
from the area. Gusts may still reach into the 35 to 45 mph range
through this evening in the cancelled areas, but strong wind gusts
are no longer expected. Even in the areas still under the warning,
high wind gusts (60 to 65 mph) will be few and far between, but
still possible.

The other update was to add a mention of scattered showers to the
southern Rocky Mountain Front area east across Cascade and Judith
Basin Counties. The decreasing wind has allowed an area of showers
to move off the mountains into these areas. The showers should not
last very long there, likely diminishing by midnight, and
additional precipitation amounts should be fairly light.



Strong winds will ease tonight but remain breezy through Tuesday,
especially over the plains. Simultaneously, precipitation along and
near the Continental Divide, and the Southwest Montana mountains,
will become scattered tonight and then end on Monday. Dry weather is
then expected through Tuesday, as are moderating temperatures.


Updated 2335Z.

VFR conditions will continue at the TFX terminals at least through
the day on Monday, but clouds and showers will likely obscure
mountain tops in western and southwest Montana through 12Z. The
strong westerly flow aloft will decrease and shift more
northwesterly through the period as the Pacific cold front exits the
area. As a result, the strong and gusty westerly surface winds at
the terminals will decrease significantly through 06Z. Low level
wind shear and mountain wave turbulence will persist overnight, but
they will both gradually decrease. Clearing skies and lighter gusty
winds are expected for Monday.


/ISSUED 535 PM MDT Sun Oct 22 2017/

Rest of today through Tuesday...A weather disturbance will exit our
CWA to the east this afternoon and evening. In its wake, a high
pressure ridge builds-in from the west through Tuesday. This pattern
will allow surface winds to ease this evening as flow aloft weakens
and the MSLP gradient relaxes in response to the aforementioned
ridge. Will keep the high wind warning in place for now and let
the evening shift reevaluate the situation later today. Upslope
precipitation along/near the Continental Divide and across the
Southwest MT mountains will become more intermittent this evening
before tapering-off on Monday. Elsewhere, just a few showers are
possible through this evening, while even a stray thunderstorm or
two cannot be completely ruled-out over Hill and Blaine Counties.
Dry weather is then expected area-wide Monday night and Tuesday
as stabilizing high pressure gains firm control. Low temperatures
will be near or slightly-above normal through the short term
period. Highs will be near-normal today and Monday before
moderating to about 10 degrees above-normal on Tuesday.

Tuesday Night through Sunday...A fast moving shortwave trough
embedded in the northwest flow aloft will drag a cold front
through the region Wednesday evening. A period of strong southwest
winds appears likely to develop in advance of the frontal
passage, possibly reaching high-wind criteria. Models are
beginning to converge on the timing for this system, but
confidence remains low regarding temperatures as winds shift to
the north and produce upslope- enhanced precipitation across much
of N-central MT. A blend of model solutions does bring temperature
below freezing Wednesday night, with snow levels lowering to the
plains/valleys. The trough moves quickly, limiting potential snow
amounts to around 1 inch at lower elevations. High amplitude
ridging over the western U.S. will provide a dry northerly flow
over Montana to end the week, with temperatures returning to near
seasonal averages.


GTF  38  57  39  66 /  20   0   0   0
CTB  35  54  37  65 /   0   0   0   0
HLN  38  57  34  65 /  20   0   0   0
BZN  33  57  30  63 /  30   0   0   0
WEY  25  46  22  53 /  50   0   0   0
DLN  31  55  30  62 /  20   0   0   0
HVR  35  58  33  65 /  20   0   0   0
LWT  34  52  33  66 /  20   0   0   0




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