264
FXUS65 KTFX 161716
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1116 AM MDT Wed Apr 16 2025

Aviation Section Updated.

.KEY MESSAGES...

 - A spring storm system will spread much cooler temperatures
   south across the area with a cold front today followed by the
   development of snow, which may be heavy at times along the
   Rocky Mountain Front.

 - Widespread snow and winter weather impacts shift to southwest
   Montana tonight with heaviest snow near the Bridger, Gallatin
   and Madison Ranges.

 - Gusty north winds will be strongest across southwest Montana tonight
   through Thursday, though the combination of winds, colder
   temperatures and moisture will create difficult conditions for
   young livestock across much of the area.

&&

.UPDATE...
/Issued 1000 AM MDT Wed Apr 16 2025/

Rain and snow has begun to push into North Central Montana this
morning, and the transition to snow has generally been a bit
faster than expected. I have lowered snow levels just a bit to
help hasten the transition through the rest of the day in line
with current trends. Ludwig

&&

.DISCUSSION...
/Issued 1000 AM MDT Wed Apr 16 2025/

 - Meteorological Overview:

A fairly potent shortwave/vorticity center diving south through the
Canadian Rockies early this morning around a larger scale trough
over western Canada will continue south through the Northern Rockies
today and tonight resulting in period of impactful weather today
through tomorrow.

First, a cold front and wind shift to the north is already through
Cut Bank and will sweep south across most of north-central MT this
morning. Meanwhile, colder air and precipitation developing in SW
Alberta will spread south this morning, several hours delayed from
the initial wind shift. An area of moderate precipitation is
expected to develop across western portions of Glacier and Pondera
counties by mid-morning as deeper northerly flow takes on more of an
upslope component combined with larger scale lift and frontogenic
forcing ahead of the disturbance dropping south along the BC/AB
border. Hi-res model ensembles are in reasonable agreement with
this, giving a 50-70% probability of snowfall rates exceeding 3/4"
per hr to areas along the east side of Glacier NP for several hrs
late this morning. This area of enhanced lift and precipitation
slides south along the Rocky Mountain Front this afternoon with
areas of less intense precipitation expanding across much of
north-central MT as well.

While temperatures remain steady or fall across most of north-
central MT today, southwest MT will remain milder until the frontal
passage, which reaches the Helena area this afternoon and the
Gallatin Valley early this evening, before continuing on to the ID
border by late this evening. Precipitation spreads south and east
across central MT this afternoon and into southwest MT this evening.
There is enough instability for an isolated thunderstorm risk this
afternoon, mainly south of I-90. Precipitation type may initially be
rain at elevations below 5000 ft, but a quick transition to snow is
expected as temperatures aloft cool quickly an tandem with the
onset of precipitation.

As the upper level disturbance continues south through ID tonight,
precipitation increases across SW MT as deeper east/northeasterly flow
develops, favoring the Bridger, Northern Gallatin/Madison and
Tobacco Root ranges for significant snowfall amounts. Models have
been consistent in focusing snowfall amounts of 8-12 inches or
more over these mountains and winter storm watches have been
upgraded to warnings. A Winter Storm Warning was also added for
the Rocky Mtn Front region with winter weather advisories
elsewhere across southwest and central MT as well as areas
adjacent to the Rocky Mtn Front.

In addition to the snow, gusty north winds will persist through
tonight and strengthen across southwest MT overnight as the surface
pressure gradient across the area strengthens between high pressure
building across MT and low pressure over WY. Snow ends from north
to south tonight across most of north-central MT and diminishes
from north to south across central ans southwest MT on Thursday,
lingering through Thursday afternoon across the SW MT mountains.
Colder air remains across the area through Thursday night with
clearing skies also expected, setting the stage for some areas to
see overnight low temperatures in the teens. A brief period of dry
and milder weather follows Friday and Saturday before the next
active weather period develops with renewed upper level troughing
across the region later this weekend into early next week.

 - Forecast Confidence & Scenarios:

Locally heavy snow developing along the east slopes of the Rocky
Mtn Front this morning will impact US-89 from the Canadian border to
Browning and US-2 from East Glacier to Marias pass. This set up,
along with gusty north winds could be particularly impactful to US-89
over the Hudson Bay Divide. Similar precipitation rates are possible
further south along the Rocky Mtn Front this afternoon, including
areas from Augusta south to Rogers Pass. Confidence in impacts
from accumulation on roads is lower this afternoon but significant
reductions in visibility are likely, particularly from Bowmans
Corner to Rogers Pass on MT-200.

In addition to heavier snow across SW MT tonight gusts in excess of
40 mph are possible through the N-S valleys of SW MT, which could be
particularly impactful to the Norris Hill area where both
significant snowfall and wind is likely.

Confidence in snowfall amounts is lowest across southwest MT valleys
where there remains a large spread in between 90th and 10th
percentile accumulation. This is greatest across the Gallatin valley,
where precipitation shadowing by the Bridgers may limit precipitation
across across areas along and north of I-90 (Belgrade) but this
effect diminishes with increasing snowfall likely south of I-90
(Gallatin Gateway).

The combined effects of temperatures in the 20s and gusty north
winds along with wet/snowy conditions will also be impactful to
young/newborn livestock across most of north-central and
southwest MT. Hoenisch

&&

.AVIATION...
16/18Z TAF Period

The primary concern this TAF period will be for a cold front
moving from north to south through the remainder of Central and
Southwest Montana this afternoon and evening, bringing
opportunities for mainly snow to the region. Ahead of the front
there will be an opportunity for a few showers and perhaps a
thunderstorm or two in Southwest Montana this afternoon. Low
vis/cigs will develop/persist in areas after the cold front moves
through, with slow improvement from north to south beginning this
evening/tonight in northern areas. Northerly winds will persist
across the region behind the front through at least tomorrow
morning. -AM

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  27  40  23 /  90  80  50  10
CTB  37  24  38  17 / 100  30  30   0
HLN  55  30  41  25 /  60  90  60  10
BZN  61  26  35  16 /  50 100  90  30
WYS  58  22  33   7 /  50  80  90  40
DLN  63  27  34  19 /  20  80  60  10
HVR  44  26  46  21 /  90  10  10   0
LWT  48  26  37  21 /  70  90  60  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until midnight MDT tonight for East Glacier
Park Region-Southern Rocky Mountain Front.

Winter Weather Advisory until midnight MDT tonight for Northern
High Plains-Southern High Plains.

Winter Weather Advisory from 3 PM this afternoon to 6 AM MDT
Thursday for Judith Basin County and Judith Gap-Little Belt and
Highwood Mountains-Snowy and Judith Mountains.

Winter Storm Warning from 3 PM this afternoon to midnight MDT
Thursday night for Big Belt, Bridger and Castle Mountains-
Gallatin and Madison County Mountains and Centennial Mountains.

Winter Weather Advisory until 6 AM MDT Thursday for Gates of the
Mountains-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory from 6 PM this evening to midnight MDT
Thursday night for Beaverhead and Western Madison below 6000ft-
Canyon Ferry Area-Elkhorn and Boulder Mountains-Gallatin Valley-
Helena Valley-Meagher County Valleys-Missouri Headwaters-
Northwest Beaverhead County-Ruby Mountains and Southern
Beaverhead Mountains.

Winter Storm Warning from 6 PM this evening to midnight MDT
Thursday night for Madison River Valley.

&&

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