557
FXUS65 KTFX 101148
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
548 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.

&&

.DISCUSSION...
/Issued 332 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...
10/12Z TAF Period

The main concern this TAF period with be a wave of showers and
thunderstorms lifting north across Southwest MT early this
morning. Mostly VFR conditions are expected; However, brief MVFR
conditions can`t be ruled out under heavier showers. This activity
should dissipate before reaching central MT, so there`s no
mention of precipitation for KHLN and KLWT at this time. Southerly
winds increase over southwest MT this afternoon and evening,
mostly for KEKS. - RCG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  49  69  34 /  10  10  90  80
CTB  69  43  63  28 /   0  10  10  80
HLN  76  48  66  37 /  30  20  90  90
BZN  76  46  67  33 /  40  10  90  90
WYS  65  40  56  25 /  40  50  90 100
DLN  71  45  61  32 /  40  20  90  90
HVR  74  44  73  33 /   0   0  20  80
LWT  77  49  69  30 /  10   0  90  90

&&

.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.

&&

$$
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