High Wind in Montana, February 11, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
1025 PM MST Mon Feb 10 2020

...Aviation Section Updated...

.SYNOPSIS...

Winds will begin to increase along the Rocky Mountain Front,
northern areas of the central Montana mountains, and in north-
south orientated valleys of southwest Montana tonight. These
strengthening winds could lead to blowing and drifting snow,
especially in areas with a deep and non-compacted snowpack. Strong
winds will impact mainly the mountains and plains Tuesday, with
snow showers developing later Tuesday into Wednesday, with most
significant accumulations confined to the central Montana
mountains.

&&

.UPDATE...

Clouds and showers have diminished across much of the forecast
area this evening. Have updated to remove PoPs for the remainder
of tonight. Latest short term model runs have trended a bit wetter
and faster with tomorrow's quick clipper system so have also
updated to slightly raise PoPs for Tuesday afternoon. Finally,
made tweaks to drop overnight lows a few degrees in areas where
temperatures have already approached or fallen below forecast
lows. This mainly affected mountains and the higher southwest
valleys including Bozeman and West Yellowstone. mpj

&&

.AVIATION...
Updated 1025 PM MST Mon Feb 10 2020 (11/06Z TAF Period)

VFR conditions are expected through 00-06z Tuesday at most terminals
in Southwest and North Central Montana; however, mid-level
cloudiness and rain/snow showers could bring periods of near-MVFR
conditions during the late morning/early afternoon hours on Monday.
Winds will continue to increase along the Rocky Mountain Front,
north of the Central Montana mountains, and in the north-to-south
orientated valleys of Southwest Montana tonight. These breezy to
strong winds will then expand east over the plains of North Central
and Central Montana by the mid- to late morning hours on Monday. Low
level wind shear and mountain wave turbulence will become a concern
at some terminals during the day on Monday, especially those
immediately downwind of the Continental Divide. Mountain obscuration
will become increasingly likely Monday afternoon/evening. - Moldan

&&

.PREV DISCUSSION...
/ISSUED 430 PM MST Mon Feb 10 2020/

Rest of this Afternoon through Tuesday...

Primary forecast concerns over the period are strong winds late
tonight through Tuesday afternoon, and then snow/snow amounts
Tuesday afternoon into Wednesday.

Subsidence and drier air working in behind the shortwave trough
currently crossing the area from north to south will bring another
period of clearing skies late this afternoon and evening, with
surface winds backing to south to west along and west of the
Interstate 15 corridor in north-central and central Montana.

By early this evening, the surface pressure gradient along the
Rocky Mountain Front, northern portions of the central Montana
mountains, and north-to-south orientated valleys of southwest
Montana will begin to strengthen rapidly in response to a
strengthening surface high over western Wyoming as well as a
southeastward-advancing surface low from the Gulf of Alaska to
southern Saskatchewan by Tuesday afternoon. This strengthening
pressure gradient will yield increasing south to west surface
winds in these areas, which combined with recent snowfall could
lead to blowing and drifting of snow, especially in areas where
the snowpack is deep and non-compacted. Winds will become
especially strong along the Rocky Mountain Front and possibly out
as far east as Cut Bank by the early morning hours on Tuesday as
the H700 cross barrier flow and ridgetop stability increases,
leading to mountain wave activity.

Tuesday will see both strong to potentially high winds over north-
central and central Montana, and more mountain snow across the
entire CWA. Winds will continue to increase and spread further east
over the remainder of the plains Tuesday morning as mixing occurs,
with most locations seeing sustained wind speeds of 20-30 kts and
gusts of 35-45 kts. While some wind prone areas along the Rocky
Mountain Front will undoubtedly see gusts approaching 50 kts Tuesday
morning and afternoon, at this point in time we do not see these
wind gusts materializing further east over the plains. Nonetheless,
difficult travel conditions for high-profile vehicles and those
pulling trailers will be possible across the northern half of the
CWA on Tuesday. The next shortwave within the moist, northwest flow
aloft begins to approach the Northern Rockies Tuesday afternoon,
which will lead to increasing precipitation chances over the
mountains and some lower elevations. Given the timing of this
shortwave and steepening lapse rates aloft, precipitation Tuesday
afternoon will likely be convective in nature, which will allow for
precipitation to possibly reach over the plains despite the
downsloping winds. Areas like the Little Belts could see moderate to
at times heavy snowfall from these convective snow showers, which
could impact travel from near Kings Hill Pass to Belt.

Tuesday Night through Next Monday...

Following the passage of the shortwave disturbance through MT late
Tuesday a NNW flow aloft is re-established across the region
allowing a colder airmass from Canada to slide SE into eastern MT
and the Dakotas on Wednesday. Moist NW flow with embedded
disturbances will support snow showers across much of the area
Tuesday night before tapering off early Wednesday. Again looking at
the greatest concentration of snow showers and a period of northerly
upslope enhancement favoring central MT with the greatest snow
accumulation. Isolated snow accumulations over 6 inches are possible
across the highest elevations of the Little Belts and Snowies with 1-
3 inches possible across adjacent lower elevations areas of Cascade,
Judith Basin, Fergus and Meagher counties. A period of gusty N/NW
winds is also possible across the north-central plains Tuesday night
as the colder airmass moves in from the north. While the brunt of
the cold airmass slides east of the forecast area Wednesday,
temperatures will be a bit cooler than seasonal averages and may
remain in the 20s across the north-central MT plains. Temperatures
still look to rebound quickly on Thursday as upper level ridging,
which has been situated to our west, shifts east across the northern
Rockies and MT as the overall upper level flow de-amplifies. This is
followed by a fairly rapid succession of Pacific weather
disturbances east across the NW US next weekend. Timing of these
features is difficult at this time range but the overall pattern
looks to support additional rounds of mainly mountain-focused
precipitation with temperatures fluctuating around seasonal averages
for mid-February. - Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  18  41  19  29 /   0  30  60  40
CTB  15  40  15  27 /  10  20  50  20
HLN  15  40  22  34 /   0  20  50  40
BZN   0  36  20  33 /   0  30  50  40
WYS -11  20   7  26 /  10  50  50  30
DLN   5  33  20  33 /   0  10  10  10
HVR  14  41  16  24 /  10  40  50  10
LWT  12  37  16  26 /  10  30  70  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

http://www.weather.gov/greatfalls