High Wind in Montana, December 30 to 31, 2019

Area Forecast Discussion
National Weather Service Great Falls MT
416 PM MST Mon Dec 30 2019

...Updated Aviation Discussion...

.SYNOPSIS...

An active weather pattern develops across Montana this week as a
series of Pacific storm systems move across the region.
Temperatures will increase through mid-week, especially east of
the Divide where gusty winds could cause issues at times. Snow
will increase on Tuesday over the mountains of western and
southwest Montana and may be heavy at times on New Years eve and
day along the Continental Divide.

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.DISCUSSION...

Upper level ridging from the Pacific NW to the Canadian prairies
will become suppressed tonight through Tuesday as a potent upper
level jet and accompanying plume of Pacific moisture moves onto
the BC/WA coast. Jet and moist plume noses into the Northern Rockies
late Tuesday then orients more northwesterly and sags southward
on Wednesday as a surface low emerges east of the Canadian Rockies
and kicks out across the Prairies. Main hazards associated with
this system will be strong winds across portions of north-central
MT and mountain snow along the continental divide affecting the
forecast area primarily late Tuesday through Wednesday afternoon.

Winds increase tonight through Tuesday morning along the east slopes
as the surface pressure gradient increases across the Rockies with
strong gusts possible by Tuesday morning along areas immediately
east of the Rocky Mtn Front. By Tuesday night strong winds are
likely to expand further east as strongest winds aloft and an
embedded mid level shortwave moves across the region and will
expand the High wind watch to include areas as far east as I15 and
across into Judith Basin county. Period of strongest winds looks
to continue through at least Wednesday morning for these areas.
With favorable temp/wind profiles for enhanced downslope winds
expected east of the Rocky mtn Front will upgrade these areas
including all of Glacier county to a high wind warning.

Snow beginning tonight along the continental divide near Marias pass
is initially light through Tuesday afternoon, but increases in
intensity Tuesday night as the main core of Pacific moisture moves
into the area. As this axis of moisture becomes more NW to SE
oriented late Tuesday night and Wednesday snow intensifies across
areas further south along the divide, including NW portions of
Beaverhead county and along the Idaho border east to West
Yellowstone. A winter storm watch continues for the mentioned
areas in SW MT. The Winter storm watch will be upgraded to a
warning for areas above 5000ft along the Rocky Mtn Front where
winds will also be an issue traveling east of the Divide. While
precipitation also decreases east of the continental divide,
there will likely be a transition zone to high winds with
potential for snow to be transported further east, affecting areas
between Marias Pass and East Glacier. On Wednesday, some snow
showers are also possible across the remainder of the forecast
area as flow turns northwesterly and additional disturbances move
through. This could bring some minor snow accumulations of an inch
or less to areas of central and SW MT adjacent to the mountains
with little or no snow accumulation elsewhere across the plains.
Hoenisch

Wed night thru next Mon... A messy and active northwest flow looks
to persist later this week into the weekend, with periods of snow
likely, especially for the mountains from Rogers Pass thru the
Canadian border. The timing of the heaviest snow remains somewhat
uncertain, with run-to-run consistency and agreement between the
models not the best we could hope for so far, but significant
additional snowfall remains possible in the mountains. A high wind
event appears increasingly likely later this week into the weekend
as a low pressure system passes to the north while high pressure
builds over the Great Basin and central Rockies. -Kredensor

&&

.AVIATION...
Updated 416 PM MST Mon Dec 30 2019 (31/00Z TAF Period)

VFR conditions will prevail at most terminals with clear skies but
some increase in high cloud-cover tonight. Surface winds will
gradually increase later through tonight along the east slopes of
the Rockies. By Tuesday afternoon, gusts to 30kts are possible at
KGTF and KCTB with gusts increasing to 50kts locally along the Rocky
Mtn Front. These winds will increase and spread further east across
western portions of north-central MT Tuesday afternoon and Tuesday
night.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  26  43  36  46 /   0   0  50  40
CTB  25  40  32  43 /   0   0  30  30
HLN  18  39  31  43 /   0  10  60  50
BZN  11  34  22  40 /   0  10  70  60
WYS  -3  19   8  25 /  10  20  90  90
DLN  12  29  20  37 /   0  20  60  70
HVR  20  40  32  43 /   0   0  50  40
LWT  19  40  32  43 /   0   0  40  40

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.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Tuesday afternoon through Wednesday
evening Beaverhead...Gallatin...Madison.

High Wind Watch from Tuesday afternoon through Wednesday morning
Cascade...Eastern Pondera...Eastern Teton...Judith Basin...Toole.

High Wind Warning from 5 AM Tuesday to 11 AM MST Wednesday
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

Winter Storm Warning from 5 PM Tuesday to 8 PM MST Wednesday
above 5000 feet for Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

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http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
830 PM MST MON DEC 30 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0754 PM     NON-TSTM WND GST 2 SE BROWNING           48.54N 112.98W
12/30/2019  M57 MPH          GLACIER            MT   DEPT OF HIGHWAYS

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