777
FXUS65 KTFX 101725
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1125 AM MDT Fri Oct 10 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Mild and mostly dry conditions expected today except for a few
   showers or thunderstorms and gusty winds over the southwest.

 - Saturday will be a transition day with breezy to 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.

&&

.UPDATE...
/Issued 837 AM MDT Fri Oct 10 2025/

Minor adjustment made to PoPS this morning, mainly to expand the
areal coverage of low chance (i.e. 10-20%) precipitation further
north to near the MT Hwy 200 corridor in Central Montana east of
Great Falls. Additionally, extended the temporal coverage of low
chance PoPs across Southwest Montana several hours longer given
recent satellite and radar trends. Otherwise the remainder of the
forecast remains on track. - Moldan

&&

.DISCUSSION...
/Issued 837 AM 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...

There will be sufficient moisture and instability for scattered
to numerous showers and thunderstorms on Saturday. The showers and
storms will be capable of mixing down 30 to 40 kt lower and mid-
level winds to the surface as well as producing small hail.
Localized heavy downpours will be another concern, primarily for
the more flood prone burn scars over central and southwest MT. The
Weather Prediction Center has painted areas south and east of a
Helena to Lewistown line in a marginal risk for flooding from
excessive rainfall, meaning there is a 5 to 10% chance for
excessive rainfall exceeding flash flood guidance.

Snow Saturday night through Monday...

Snow levels begin to fall in a northwest to southeast fashion
Saturday evening through early Sunday. 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.
There are concerns for some heavier bursts of snow at Bozeman Pass
and even in Bozeman proper, but with the core of the
precipitation expected to fall during the day, I held off for
adding these areas to the winter storm watch for now. Impacts in
the southwest will be greatest for outdoor interests in the
mountains and for those traveling on snowy/muddy forest roads.
- RCG

&&

.AVIATION...
10/18Z TAF Period

VFR conditions will prevail across all terminals during this TAF
Period outside of during any thunderstorms. At the KEKS, KWYS, and
KHLN terminals between 11/15Z and 11/18Z there is a 15 - 30% chance
for thunderstorms. At the KBZN terminal between 11/18Z and 11/24Z
there is a 20 - 30% chance for thunderstorms. Any thunderstorm
will produce gusty, erratic winds, and a heavy downpour in
addition to lightning. From 11/03Z through the end of the TAF
Period there will be isolated instances of low-level wind shear
and mountain wave turbulence. -IG


&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  77  49  68  34 /  10  20  40  70
CTB  69  42  61  28 /   0  10  10  70
HLN  77  48  65  36 /  30  20  70  80
BZN  76  45  63  33 /  40  20  90 100
WYS  65  40  54  25 /  40  70  90 100
DLN  72  45  62  31 /  40  50  80  80
HVR  76  45  72  30 /   0  10  10  60
LWT  77  49  69  31 /  10   0  90 100

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Saturday evening through Monday morning
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