908
FXUS65 KTFX 102340
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
540 PM MDT Fri Oct 10 2025

Aviation Section Updated.

.KEY MESSAGES...

 - A significant pattern change begins on Saturday, with a
transition to breezy and windy condtions and scattered to numerous
showers and thunderstorms. A few storms may contain heavy downpours
and pose a localized flooding risk to susceptible burn scars.

 - Widespread precipitation, mostly mountain snow, and much cooler
temperatures are expected Saturday night through Monday.

 - Below average temperatures continue for at least the first half
of next week with day to day scattered shower activity and mountain
snow.

&&

.DISCUSSION...
/Issued 248 PM MDT Fri Oct 10 2025/

 - Meteorological Overview:

Southwesterly flow aloft becomes established over the Northern
Rockies today in response to a trough moving into the Pacific
Northwest. An an initial shortwave will bring a few widely scattered
showers and perhaps a few thunderstorms to southwest MT this morning
before additional waves send scattered showers and thunderstorms
through the region again tonight into Saturday. Strengthening south
to southwesterly H700 winds on the order of 30 to 40 kts will bring
breezy to windy conditions to the southwest today, with winds also
increasing along the Rocky Mountain Front tonight into Saturday. The
southwesterly flow will also advect moisture northward into the
region with precipitable water values approaching the 0.75 inch mark
for areas along and southeast of a Dillon to Havre line on Saturday.
This combined with CAPE values in the 100 to 400 J/kg level may
result in some storms producing localized heavy downpours in
addition to isolated instances gusty winds, and hail.

The main trough moves into the Northern Rockies Saturday night into
Sunday with the south end of the system becoming sheared off from
the general circulation. Although this adds at least some
uncertainty to the forecast, there`s a general expectation for the
most widespread precipitation to occur Between Saturday night and
Monday with H700 temperatures falling to around -10C over
central/north-central MT. Despite the cold air aloft being a little
disjointed from the areas of heaviest precipitation, generally
expected along and southeast of a Butte to Havre line, these mid-
/low level temperatures will be sufficient to support heavy snow in
the mountains and at least some lower elevation accumulations.
Snowfall will initially be driven by forcing from the trough/cold
front, but will shift to warm air advection and isentropic lift in
addition to low level easterly flow later Sunday into Monday.

Another trough dives into the Pacific Northwest and maintains
general low grade troughing over the Northern Rockies early next
week before weakening and swinging northeastward into Montana later
in the week. This will result in continued below average
temperatures and day to day lower end shower activity and mountain
snow for much of the week. - RCG

 - Forecast Confidence & Scenarios:

Showers and thunderstorms on Saturday...

Southwesterly flow aloft ahead of the approaching upper level trough
and attendant Pacific front will help to transport anomalously high
(2.5 to 3.5 standard deviations above normal) precipitable water
(PWATs) over portions of Southwest and Central Montana, generally
along and southeast of a Butte, to Helena, to Lewistown line. These
anomalously high PWATs of between 0.6-0.8" combined with increasing
ascent from the aforementioned front and upper level trough will
help to support the potential for localized heavy rainfall,
especially over or near the higher terrain beneath the stronger
thunderstorms. Fast storm motions of between 30-40 mph will help to
limit the residence time and overall (widespread) threat of flooding
across Southwest and Central Montana, but localized flooding can not
be ruled out. Susceptible areas like recent burn scars and urban
areas near the mountains (i.e. Bozeman, Helena, and Lewistown) have
the highest, albeit a 5-10%, chance of seeing heavy rainfall that
would lead to flooding. - Moldan

Snow Saturday night through Monday...

Snow levels will be falling throughout the entire day on Saturday
and into the day on Sunday as an upper level trough and attendant
fronts (initial Pacific cold front on Saturday followed by a
Canadian cold front Saturday night/Sunday) move across the Northern
Rockies. Snow levels at 06z Saturday of 9-12kft will fall to around
to 6-9kft by 00z Sunday as the aforementioned Pacific cold front
sweeps east across Southwest through North Central Montana, with
snow levels then plummeting to around 2.5-5kft from 03-12z Sunday in
a northwest to southeast fashion as the Canadian cold front dives
south. Heavier precipitation rates during the evening and overnight
hours on Saturday will lead to strong dynamic cooling processes,
which will lead to areas of lower snow levels than previously
mentioned; with the NBM 10 Percentile values (representing a
realistic low end snow snow level) generally being 0.5-1.5kft lower
than the deterministic NBM snow levels (previously mentioned). These
heavier burst of precipitation have the potential to lead to
accumulating snow across lower elevations and additional mountain
passes outside of the current winter weather highlights, but
uncertainty on exact timing and overall coverage has lead me to
refrain from issuing additional winter highlights at this time.

The heaviest snow for northern areas is expected along the Rocky
Mountain Front and the adjacent foothills to the east followed by
the central island ranges and their northerly upslope foothills.
These areas stand a 70 to 90% + chance for 6 inches of snow over a
48 hour period ending 6 pm Monday. Plains locations west of I15 and
along highway 200/87 from Rogers Pass to the Geyser area have a 30
to 40% chance for seeing 3 inches or more of snow for the same
timeframe, though much of this may be melted by warmer surface
temperatures. Impacts will be greatest in the Glacier National Park
area where outdoor recreation may become dangerous in addition to
park routes becoming impassible and snow induced power outages.

Mid-level temperatures will not be as cold in the southwest, though -
5 to -10C H700 temperatures will still be cold enough to lower snow
levels to the surface at least briefly. additionally, the core of
heaviest QPF is expected here with mountain areas southeast of a
Dillon to Bozeman line seeing probabilities of 50 to 70% chance for
1 inch of liquid equivalent precipitation Saturday evening through
Monday evening. Given the setup, the Madison and Gallatin ranges
above 6,000 feet will see the highest snow totals with probabilities
for 6 inches of snow or more running in the 50 to 70% chance range
for the same timeframe. - Moldan/RCG

&&

.AVIATION...
11/00Z TAF Period

Initial concerns this TAF period include a round of showers and
isolated thunderstorms across mainly Southwest Montana tonight.
Additionally, instances of LLWS will be around, though are low
confidence in being sustained - hence mention has been withheld
from TAFs at this time.

Moving toward daytime hours Saturday, concern turns to showers and
perhaps a few thunderstorms, mainly across Southwest Montana.
Showery precipitation transitions to be more stratiform in nature
late Saturday afternoon and evening, again largely impacting
Southwest Montana. As this transition occurs, ceilings fall, along
with snow levels as the area trends cooler. -AM

&&

.HYDROLOGY...

As showers and thunderstorms push into the area on Saturday, a few
of the showers and storms may produce some highly localized heavy
rainfall. While widespread flooding is not expected at this time,
there is a low (5% or so) chance that a burn scar flash flood
could occur at either Horse Gulch or West Fork Burn Scars. Ludwig

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  68  31  38 /  20  40  70  80
CTB  42  61  28  33 /  10  10  70  80
HLN  48  65  36  42 /  20  70  80  80
BZN  45  63  33  44 /  20  90 100  70
WYS  40  54  25  36 /  70  90 100  80
DLN  45  62  31  46 /  50  80  80  40
HVR  45  72  30  41 /  10  10  60  60
LWT  49  69  31  38 /   0  90 100  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 6 PM Saturday to noon MDT Monday for
East Glacier Park Region-Southern Rocky Mountain Front.

Winter Storm Watch from Saturday evening through late Sunday
night for Gallatin and Madison County Mountains and Centennial
Mountains-Little Belt and Highwood Mountains.

&&

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