924
FXUS65 KTFX 111712
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1112 AM MDT Sat Oct 11 2025

Aviation Section Updated.

.KEY MESSAGES...

- A significant pattern change begins today, transitioning to
  breezy to windy conditions with scattered to numerous showers
  and thunderstorms.

- Widespread precipitation, accumulating snow, and much
  cooler temperatures are expected tonight through Monday.

- Temperatures warm slightly next week, but there will be day to
  day opportunities for scattered shower activity and mountain
  snow.

&&

.DISCUSSION...
/Issued 551 AM MDT Sat Oct 11 2025/

 - Meteorological Overview:

Southwesterly flow aloft continues today while a Pacific trough
approaches from the west. This will advect moisture northward into
the region and bring scattered to numerous shower activity and
isolated thunderstorms. Precipitable water values approaching the
0.75 inch mark combined with CAPE values in the 100 to 400 J/kg
level may result in a few storms producing localized heavy
downpours in addition to isolated instances gusty winds, and
perhaps some hail, mostly for areas along and southeast of a
Dillon to Havre line. South to southwesterly H700 winds on the
order of 25 to 35 kts will bring breezy to windy conditions today,
most notably to the southwest mountain peaks, the south to north
oriented southwest valleys, and areas along the along the Rocky
Mountain Front.11/18Z TAF Period

VFR conditions will prevail across all terminals during the
beginning of this TAF Period before rain and/or snow cause
visibility and ceilings lower to at least MVFR levels. At all but
the KGTF, KCTB, and KHVR terminals between now and 12/06Z there is a
15 - 30% chance for thunderstorms. Any thunderstorm will produce a
heavy downpour, lightning, and gusty, erratic winds. After 12/12Z
across all terminals except for the KBZN terminal there will be a
rain/snow mix or all snow with at least MVFR-level visibility and
ceilings. During the majority of this TAF Period there will isolated
instances of low-level wind shear and mountain wave turbulence.
During the majority of this TAF Period there will be mountain
obscuration. -IG

The main trough swings into the Northern Rockies and brings
periods widespread precipitation tonight through Monday with H700
temperatures falling to around -10C over central/north-central MT
following a Canadian cold frontal passage. These middle and low
level temperatures will be sufficient to support heavy snow in the
mountains and at least some lower elevation accumulations. There
will be two distinct periods of snow to focus on, with the first
being driven by forcing from the trough/cold front tonight through
Sunday morning. There will be a general lull in activity during
the day on Sunday before warm air advection/isentropic lift and
low level easterly flow initiate the second round Sunday night
into early Monday. This second round will be mostly focused along
the Rocky Mountain Front and the plains.

The southern portion of the main trough shears off and quickly
weakens as it heads off to the east early next week while the
stronger northern portion of the circulation strengthens and
retrogrades southwest towards the Pacific coast. Most ensembles
favor weak difluent flow aloft over the Northern Rockies for
continued below average temperatures and day to day lower grade
shower and mountain snow activity for the first half of the week.
The Pacific Northwest trough then moves into Montana late
Wednesday through Friday, though the precise details of the
trough`s evolution is unclear at this time. Overall, there`s an
expectation for increased precipitation and mountain snow for the
second half of the workweek while temperatures warm slightly.
- RCG

 - Forecast Confidence & Scenarios:

Showers and thunderstorms today...

There will be sufficient moisture and instability for scattered
to numerous showers and isolated thunderstorms today, mostly over
central and southwest MT. The showers and storms will be capable
of mixing down 25 to 35 kt lower and mid- level winds to the
surface, though probabilities for convective wind gusts over 35
mph drops off to less than 30% this afternoon according to the
latest HREF ensembles. Isolated instances of heavy downpours may
pose a 5% chance localized flooding risk to susceptible burn
scars, namely the Horse Gulch and West Fork burn scars.

Snow Saturday night through Monday...

Snow levels begin to fall in a northwest to southeast fashion late
this afternoon through early Sunday. Central and Northern areas will
have two distinct periods of more widespread snow, the first tonight
into Sunday morning and then again Sunday night into Monday morning.
The heaviest snow for northern areas is still 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 at least some of this may be melted by warmer
surface temperatures, especially during the first period of snow
tonight and Sunday morning. Impacts will be greatest in the Glacier
National Park area where outdoor recreation may become dangerous
with near or impassible park routes. Snow induced infrastructure
failures and power outages can also be expected. Changes to the
winter weather highlights included an upgrade of the Little Belts
zone to a winter weather advisory and then adding the Rocky Mountain
Front high plains zones and MacDonald Pass areas to the advisory as
well. Additional advisories will be considered by future shifts for
central and north-central areas Sunday night into Monday, including
the canyon area between Helena and Great Falls.

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 this evening through
Sunday. 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. Impacts in the southwest will be greatest for
outdoor interests tonight through Sunday morning for areas in the
mountains and for those traveling on snowy/muddy forest roads. The
winter storm watch for the Madison/Gallatin ranges was upgraded to a
winter weather advisory, although the time was limited to tonight
and Sunday morning. - RCG

&&

.AVIATION...
11/18Z TAF Period

VFR conditions will prevail across all terminals during the
beginning of this TAF Period before rain and/or snow cause
visibility and ceilings lower to at least MVFR levels. At all but
the KGTF, KCTB, and KHVR terminals between now and 12/06Z there is a
15 - 30% chance for thunderstorms. Any thunderstorm will produce a
heavy downpour, lightning, and gusty, erratic winds. After 12/12Z
across all terminals except for the KBZN terminal there will be a
rain/snow mix or all snow with at least MVFR-level visibility and
ceilings. During the majority of this TAF Period there will be
isolated instances of low-level wind shear and mountain wave
turbulence. During the majority of this TAF Period there will be
mountain obscuration. -IG

&&

.HYDROLOGY...

As showers and thunderstorms push into the area today, 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.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  34  38  26 /  30  80  90  90
CTB  63  29  35  21 /  10  80  80  80
HLN  65  35  43  26 /  60  80  90  90
BZN  68  33  49  26 /  90 100  60  40
WYS  54  23  39  16 /  90  90  70  10
DLN  63  32  50  28 /  70  80  20  30
HVR  73  32  41  22 /  30  60  60  30
LWT  70  30  40  24 /  70  90  70  60

&&

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

Winter Weather Advisory from midnight tonight to noon MDT Monday
for Little Belt and Highwood Mountains-Northern High Plains-
Southern High Plains-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory from 9 PM this evening to noon MDT
Sunday for Gallatin and Madison County Mountains and Centennial
Mountains.

&&

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