Winter Storm Warning 2, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1004 AM MST Mon Feb 6 2023

.SYNOPSIS...

An approaching weather system will continue to bring accumulating
mountain snow to Central and Southwest Montana this morning, with
around 2 to 5 inches expected over Raynolds, Targhee, Bozeman,
Deep Creek, and Kings Hill Passes. Attention then turns to
increasing westerly winds across the plains of Central and North
Central Montana from Monday night into Tuesday, with high winds
expected along the Rocky Mountain Front and adjacent plains.

&&

.UPDATE...

Snow has dissipated across most of Southwestern Montana this
morning, with just a few leftover snow showers over the higher
terrain. With this in mind, we have cancelled the Winter Weather
Advisory a little bit earlier than originally anticipated. Ludwig

&&

.AVIATION...
1004 AM MST Mon Feb 6 2023 (06/18Z TAF Period)

Low to mid-level cloudiness will persist over Southwest and Central
Montana throughout the TAF period as Pacific moisture streams
eastward and across the Northern Rockies. This will bring low
VFR/MVFR conditions to the KBZN and KEKS terminals through the
06/21z to 07/03Z timeframe, thereafter CIGS will gradually improve
to VFR/low VFR. Mountains will be obscured throughout the entire
0618/0718 TAF period, especially along the Continental Divide.
Increasing low to mid-level west winds will also bring strong and
gusty surface winds to the valleys and plains of Central and North
Central Montana from the late afternoon/early evening hours through
Tuesday morning. Mountain wave activity, potentially very strong
immediately downwind of the Rocky Mountain Front, will become
increasingly likely between 07/00z and 07/15z. Additionally,
instance of low-level wind shear will also be possible over this
timeframe at the terminals across the North Central Montana
plains.

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PREV DISCUSSION...
/ISSUED 352 AM MST Mon Feb 6 2023/

This Morning...

No changes were made to the existing Winter Weather Advisory for the
mountains of southwest and central Montana. Snow will gradually
diminish during the late morning hours over this area, though light
snow will continue along the Northern Rockies including Marias Pass
with light snow accumulations.

This Afternoon through Tuesday...

Transient ridging over the Northern Rockies today will quickly be
flattened out by an approaching shortwave trough this evening, with
zonal flow then expected over the Northern Rockies through Tuesday
afternoon. This flattening of the upper level ridge combined with
increasing cross barrier flow and a strengthening surface pressure
gradient along the Rocky Mountain Front will lead to increasing
southwest to west surface winds from Monday afternoon and through
the morning hours on Tuesday over the plains of Central and North
Central Montana. SPC HREF ensemble max wind gust guidance depicts
wind gusts pushing right up to, but perhaps not quite reaching,
the 60-mph gust threshold for a High Wind Warning over north-
central Montana especially on the eastern slopes of the mountain
ranges. However, strongest surface winds will be across the
Eastern Glacier Park Region, Southern Rocky Mountain Front,
Northern and Southern High Plains, and Eastern Glacier/Western
Toole/Central Ponder Counties. These gusty winds will be further
enhanced beneath mountain wave activity, with latest BUFKIT
sounding data supporting a very favorable environment (i.e.
ridgetop stability) for mountain waves to develop and propagate
eastward over the plains. Current NBM probabilistic data supports
a 75-85% chance for wind gusts of 48kts or higher at St Mary,
Gleason, and Cut Bank, with a 90-100% chance for 48kts or higher
at Browning and Dellwo through Tuesday morning. Even more
impressive is the probability for sustained winds of 34kts or
higher at Cut Bank and Browning from Monday afternoon/evening
through Tuesday morning, which is between a 70-90% chance. Given
the strong deterministic and probabilistic support for high winds
through Tuesday morning for the Eastern Glacier Park Region,
Southern Rocky Mountain Front, Northern and Southern High Plains,
and Eastern Glacier/Western Toole/Central Pondera Counties, the
High Wind Warning continues from 21z Monday/01z Tuesday through
17z Tuesday. Despite another potential High Wind event Tuesday
evening, decided it was best for the High Wind Warning to expire
at 17z Tuesday given a 12hr window of sub- warning level wind
speeds across the warned area. -CC/Moldan

Tuesday night through next weekend...

The aforementioned trough responsible for increased winds across the
region Monday and Tuesday will continue its approach Tuesday night,
crossing over the region Wednesday. Much like the system expected
across the region today, most precipitation is expected to be
reserved for terrain, and looks to be relatively light in nature at
this time for most areas except along the immediate Continental
Divide across the Glacier Park region. The probability for snow in
excess of 6 inches is around 65-70% across Marias Pass from Tuesday
evening through Wednesday. The probability for snow in excess of 4
inches across the highest peaks of Southwest Montana is running
generally below 50% over the same time period, except along the
Continental Divide toward Chief Joseph Pass where there is ~80%
probability.

The second impact from this system is expected to be another round
of stronger westerly winds across the plains Wednesday morning. A
brief period of lower wind speeds is expected across the plains
Tuesday evening before a surface trough begins to redevelop in lee
of terrain late Tuesday night. Probabilities for gusts in excess of
55 mph that are greater than 50% reside along the immediate eastern
slopes of the Rocky Mountain Front and into the Cut Bank area. This
time period is also included in the current High Wind Watch in
effect along the Rocky Mountain Front. Cooler temperatures are
expected to filter into the region Wednesday evening and overnight,
especially across Southwest Montana, with some models indicating
upslope snow over the mountains and adjacent northwest-facing slopes
Wednesday afternoon into Wednesday night.

From Thursday through next weekend, ensemble clusters generally
agree in upper ridging Thursday gradually transitioning to weak
upper troughing by the end of next weekend. Generally mild
temperatures for mid-February are expected during this time, with
over half of the ensemble clusters generally dry or with light
precipitation. However, about 35-45% of the ensemble clusters do
bring some precipitation primarily to the western and southwestern
Montana mountain regions for at least a part of next weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  45  34  45  32 /  10   0   0  10
CTB  41  33  43  29 /   0   0   0  10
HLN  40  30  43  28 /  10   0   0  50
BZN  35  18  38  20 /  30   0   0  50
WYS  31  10  27  12 /  40  10   0  70
DLN  35  20  36  19 /  10   0   0  40
HVR  37  28  41  28 /  10   0   0  10
LWT  39  28  44  28 /  40   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 2 PM this afternoon to 10 AM MST Tuesday
for East Glacier Park Region-Northern High Plains-Southern High
Plains-Southern Rocky Mountain Front.

High Wind Watch from Tuesday evening through Wednesday afternoon
for East Glacier Park Region-Eastern Glacier, Western Toole, and
Central Pondera-Northern High Plains-Southern High Plains-
Southern Rocky Mountain Front.

High Wind Warning from 6 PM this evening to 10 AM MST Tuesday
for Eastern Glacier, Western Toole, and Central Pondera.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1222 PM MST MON FEB 6 2023

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

0734 AM     NON-TSTM WND GST 1 SSE CHRISTINA         47.37N 109.31W
02/04/2023  M59 MPH          FERGUS             MT   MESONET

            MEASURED AT KMTHILGE5.

&&

HART