High Wind in Montana, February 13 to 14, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
1050 AM MST Thu Feb 13 2020

Aviation Section Updated.

.UPDATE...

Areas of dense freezing fog persist this morning over eastern
Glacier and Toole counties. This fog will erode through late
morning with increasing west winds. Web cams reveal areas of
blowing snow with wind gusts to around 45 mph along the Rocky
Mountain Front. We continue to anticipate additional areas of
drifting snow to develop southeast of Great Falls into Judith
Basin County. The overall forecast describes these hazards well,
and an update will not be posted this morning.

&&

.SYNOPSIS...

Gusty west to southwest winds will develop develop over portions
of north- central Montana today and tonight and may lead to areas
of blowing and drifting snow where a fresh snow-cover exits.
Temperatures warm today despite the cold start this morning in
many areas reaching near seasonal averages this afternoon. Th next
weather system will bring snow to areas along the continental
divide late tonight with snow showers possible across southwest
Montana Friday.

&&

.AVIATION...
Updated 1050 AM MST Thu Feb 13 2020 (13/18Z TAF Period)

Northerly flow aloft over the region turns turns westerly tonight
while also increasing. VFR conditions prevail today with increasing
high cloud-cover. Surface SW winds already gusty along the immediate
east slopes of the Rockies will expand eastward today, becoming
widespread across North-central MT later this afternoon and evening.
Clouds further increase tonight with a frontal system spreading
precipitation into areas along the continental divide overnight.
Temporary IFR conditions will be possible tomorrow morning for
Southwestern terminals KBZN/KEKS/KWYS as snow bands develop along
the passing cold front.

&&

.PREV DISCUSSION...
/ISSUED 445 AM MST Thu Feb 13 2020/

Today through Friday night...Northerly flow aloft continues
today before an upper level ridge to our west shifts east across
MT tonight, ahead of the next upper trough from the Pacific to
move into the Northern rockies and MT on Friday. An area of low to
mid level cloud-cover and possibly a few flurries over eastern
and southeastern portions of the forecast area early this morning
will continue to erode while areas of fog that formed over
western portions of north-central MT overnight should also
dissipate by mid morning with the development of southwest
surface winds within a surface low pressure trough east of the
Rockies.

The lee-side trough continues to strengthen later today and
tonight as westerly flow aloft increases with gusty southwest
winds likely to overspread much of north-central MT by this
afternoon. Main concern with the increase in winds will be the
potential for blowing/drifting snow in areas where there is at
least a couple inches of fresh snow on the ground. Greatest
threat for these conditions to occur will be across southern
Cascade and much of Judith Basin county later today into tonight,
as well as areas along the immediate east slopes of the northern
Rocky Mtn Front (where gusty SW winds have already developed). A
winter weather advisory for blowing/drifting snow has been issued
for these areas. Temperatures should rebound substantially in
areas where winds develop, despite starting off in the single
digits early this morning.

The previously mentioned Pacific trough shifts across the region
Friday with an associated eastward moving front crossing central
and SW MT Friday morning. Surface winds will peak as this front
arrives Friday morning and will will also spread across SW MT at
that time and continue through Friday afternoon. A period of snow
is likely along the continental divide beginning tonight with
snow showers also possible across SW MT along and following the
frontal passage Friday. Snow accumulation will be fairly limited
at lower elevations with about 1-3 inches of new snow possible
across the mountains. Areas along the continental divide north of
Marias pass will see the greatest snow amounts with over 6 inches
possible there. Hoenisch

Saturday through next Thursday...primary forecast concern and
biggest impact to the region will be accumulating and blowing snow
Saturday night through Sunday night.

Transient ridging, within west northwest flow, will slide over the
Northern Rockies during the morning and afternoon hours on Saturday.
At the surface, a weak pressure gradient will remain along the Rocky
Mountain Front, northern foothills of the Central Montana mountains,
and across the north-to-south orientated valleys of Southwest
Montana. This surface pressure gradient, combined with diurnal
mixing up to H700 (per BUFKIT analysis) where winds of 25-50kts will
reside over the region, will lead to breezy and at times strong
winds during much of the day on Saturday. Any fresh snow from
Friday's disturbance that has not yet settled/compacted will be
susceptible to at least some drifting over this timeframe. H500
height falls will then begin to overspread the Northern Rockies
Saturday night as a shortwave trough over the Pacific Northwest digs
southeast towards the Great Basin (by Monday morning). This will
promote increasing precipitation, in the form of snow, chances
across the mountains of the CWA Saturday night (it should be noted
that precipitation will already be on-going during the day on
Saturday along the Continental Divide). By Sunday morning,
precipitation chances will begin to expand further out over the
plains and valleys of the CWA as a warm front lifts northeast across
the region. By Sunday afternoon/evening, a cold front will then
advance south from Alberta and across the region, bringing
additional chances for precipitation to the CWA, especially in the
mountains and northern facing upslope regions. 6hr pressure rises
behind this southward advancing cold front of 5-10mb will likely
lead to a period of gusty northwest/north winds, which combined with
the falling/fallen snow could lead to reduced visibilities. Snowfall
accumulations from Saturday night through Sunday night of 1-3" will
be possible over the plains and in the valleys, with 6-12" being
possible in the mountains. Ridging then begins to build and slide
east during the first half of the next work week, but northwest-to-
northerly flow aloft will likely support some mountain snow Monday
through Tuesday. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  27  41  24 /   0   0  10   0
CTB  40  24  36  20 /   0   0  10   0
HLN  42  24  38  23 /  10  20  30   0
BZN  38  20  36  17 /  10  10  50  10
WYS  26  11  28   7 /  10  30  80  20
DLN  35  21  33  17 /   0  20  40   0
HVR  28  24  38  20 /   0  10  30  10
LWT  32  24  35  20 /  10  20  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Friday Cascade...Judith
Basin.

Winter Weather Advisory until 5 AM MST Friday Northern Rocky
Mountain Front.

&&

http://www.weather.gov/greatfalls