147
FXUS65 KTFX 232346
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
446 PM MST Sat Nov 23 2024

Aviation Section Updated.

.KEY MESSAGES...

 - Snow and pockets of blowing snow will remain a concern across
northern portions of the region through the evening.

- A period of impactful snowfall late tonight into Sunday morning
  morning across portions of Southwest Montana, including
  Bozeman.

- Coldest lows of the season across the plains Sunday night into
  Monday.

- Below average temperatures continue through the upcoming week, with
  low-end chances for light precipitation Wednesday through the
  weekend.

&&

.DISCUSSION...
/Issued 118 PM MST Sat Nov 23 2024/

 - Meteorological Overview:

An embedded wave ejecting out of a broad trough centered off the
Pacific Northwest coast will be responsible for the remaining
impacts observed across the region through Sunday afternoon. This
wave has helped carve out a surface low across central Montana this
afternoon that will shift eastward through the evening. This will
bring a few impacts to the region, including a Pacific front with
rain and snow along it this afternoon and evening, gusty winds and
blowing snow in the Cut Bank area through the evening, a low-end
chance for a rumble of thunder across Southwest Montana this
afternoon, in addition to gusty southerly winds across much of
Southwest Montana.

Behind this front temperatures cool, both at the surface and
especially aloft. The cooling aloft should finally eliminate any
remaining freezing rain/drizzle across the region by early
evening.

Mountain snow will be ongoing this evening across Southwest Montana,
but will increase at lower elevations, including the Bozeman area,
late tonight into the day on Sunday. Precipitation looks to diminish
Sunday afternoon as brief shortwave ridging builds in through the day
Monday afternoon. Clear skies and light winds will combine to result
in the coldest overnight lows of the season Sunday night into Monday
across the plains.

Looking ahead to the remainder of the week, northwesterly flow aloft
looks to become established across the Northern Rockies. Cooler than
average temperatures, with low-end chances for light precipitation
will be around much of the week.


 - Forecast Confidence & Scenarios:

This afternoon and evening:

No significant thought process changes with the ongoing system.
Forecast snow amounts on the plains adjacent to the Rocky Mountain
Front have come down a bit, but when you combine the snow with gusty
winds from a barrier jet developing this afternoon behind the
surface low, keeping the Winter Storm Warnings as-is seems
reasonable.

As the Pacific front passes across the region this afternoon and
evening, a period of rain or snow looks to accompany it. Although
low confidence on the elevation cutoff between rain and snow, a
brief period of moderate to heavy snow cannot be ruled out with the
front.

Late tonight into Sunday morning: Although the probability for 3
inches of snow in the Bozeman area into the day Sunday is only
around 10% or so, high resolution ensembles give a greater than 50%
chance for periods of visibility of less than a half-mile Sunday
morning. All in all, no changes were needed to ongoing Winter
Weather Advisories across Southwest Montana.

Sunday night into Monday:

Brief ridging will allow for a cold overnight period across the
plains Sunday night. The chance for a subzero low is greater than
80% for most areas north of the MT-200 corridor. In fact, cold
prone areas along and north of the Hi-Line have around a 50%
chance for lows of -10 or less.

Tuesday into the weekend:

Cluster guidance favors northwesterly flow across the region mid-
week toward the weekend. GEFS and EFS members are in relatively good
agreement for light snow at times Wednesday through the weekend.
Overall, the probability for 3" snow across northern areas Wednesday
morning through Friday night is 20-40%. Across Southwest Montana
that chance is less than 10%. -AM


&&

.AVIATION...
24/00Z TAF Period

North-central Montana (KCTB, KHVR): Periods of snow will continue
at times through the evening today. Winds transition to a more
northwesterly direction behind a front, bringing an opportunity
for blowing snow in the KCTB area. Mountains will remain obscured
through most of the period.

Central Montana (KGTF, KHLN, KLWT): Scattered rain/snow mix
through the evening before a break in the precip overnight.
Another round of snow is expected Saturday morning. Mountains will
remain obscured through most of the period.

Southwest Montana (KBZN, KEKS): Gusty winds will continue over the
next few hours before tapering off by midnight. Another round of
snow is expected to develop across southwest Montana Saturday
morning and taper off by the afternoon. Mountains will be obscured
through most of the period.  -thor

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   8  18   0  25 /  40  30  10  10
CTB   1  12  -9  17 /  50  30  10  10
HLN  16  27  13  37 /  30  30   0   0
BZN  20  31  13  37 /  80  60   0   0
WYS  16  29   8  30 /  80  70  10  20
DLN  21  35  15  35 /  50  40   0   0
HVR   2  16  -9  18 /  50  20   0  10
LWT   9  19   6  37 /  50  40  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 AM MST Sunday for East Glacier Park
Region-Eastern Glacier, Western Toole, and Central Pondera-
Eastern Toole and Liberty-Northern High Plains.

Winter Weather Advisory until 5 AM MST Sunday for Bears Paw
Mountains and Southern Blaine-Cascade County below 5000ft-
Eastern Pondera and Eastern Teton-Hill County-Northern Blaine
County-Northwest Beaverhead County-Southern High Plains-Southern
Rocky Mountain Front-Western and Central Chouteau County.

Winter Weather Advisory until 5 PM MST Sunday for Gallatin and
Madison County Mountains and Centennial Mountains.

Winter Weather Advisory until 11 AM MST Sunday for Big Belt,
Bridger and Castle Mountains-Gallatin Valley-Madison River
Valley-Missouri Headwaters.

&&

$$
http://www.weather.gov/greatfalls