454
FXUS65 KTFX 131911
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
111 PM MDT Sun Sep 13 2026

.KEY MESSAGES...

 - Showers and a few thunderstorms this evening

 - Windy periods through Monday.

 - After a cool start, a warming trend develops later this week
   through the weekend.

&&

.DISCUSSION...

 - Meteorological Overview:

An upper level low positioned over eastern WA this afternoon
shifts east across the Northern Rockies overnight, emerging along
the AB/MT border Monday morning then continues east through
Monday afternoon. Enhanced mid-level flow ahead of the trough and
afternoon heating/mixing continues is promoting the downward
transport of gusty south/southwest winds across portions of SW MT
with sustained south winds in excess of 30 mph and a few gusts
over 50 mph focused along the Madison River Valley, where terrain
aligns with the mid-level flow and a High Wind Warning is in
effect until 6 PM. Showers and a few thunderstorms develop ahead
of the incoming upper level low late this afternoon with coverage
increasing across central/north-central MT this evening. Gusty
winds across SW MT will diminish early this evening as mixing
decreases and an inverted surface trough and cold front begin to
shift across the region. Gusty west winds, cooler temperatures and
decreasing showers sweep east across the rest of central and
north-central MT overnight behind the passage of these features.
Another round of showers circulates around the mid-upper low as it
emerges east of the Rockies Monday morning, mainly focused along
the continental divide with a few showers tracking east across
central and north-central MT through Monday afternoon as the upper
level low tracks east. Snow levels still look to fall to around
6500 ft overnight across the Glacier NP and Rocky Mtn Front region
and eventually across the rest of north-central and SW MT by
Monday morning.

Northwest flow behind the departing upper low and a strong surface
pressure gradient thanks to low pressure deepening across ND will
support gusty winds across much of north-central MT on Monday with
strongest winds across eastern portions of central MT Monday afternoon.
Broad mid-level troughing and a lingering cool surface airmass
will remain situated over MT through Tuesday prior to flow shifting
south-southwesterly mid to late week as a weaker upper low lifts
northeast out of the CA/Great Basin region. Temperatures return to
near or slightly above normal values Wednesday through the weekend.
Model guidance displays some variance regarding the timing and extent
of moisture with the Great Basin feature; however, this system will
bring warmer air alongside shower and potential thunderstorm activity,
primarily impacting SW MT late Thursday into Friday before potentially
spreading northward across central and north-central MT over the
weekend.

 - Forecast Confidence & Scenarios:

Although mid-level lapse rates in excess of 8C/km are present late
this afternoon, the strength of convection through this evening may
be somewhat constrained by CAPE values generally remaining below
500 J/kg. Nevertheless, mid-level wind speeds and shear increasing
to 50 kt will sustain a threat for gusty winds and possibly even
some small hail in stronger cells. High-resolution model ensembles
target the Great Falls to Havre corridor for the highest concentration
of showers and thunderstorms between 6 pm and 9pm, with weaker
activity shifting east across JB, Fergus and Blaine counties by
midnight.

Snow showers later tonight through Monday morning will primarily
affect the higher peaks along the continental divide north of MT-200
with up to 1 inch of snow accumulation possible at Logan Pass in
Glacier NP. Additional showers circulating across the central MT
mountains Monday morning could see some enhancement across the
Little Belts with a period of snow showers bringing some minor
accumulation to the Kings Hill area as well.

High Wind Watches remain in effect for portions of Judith Basin and
Fergus counties on Monday, where there is a broad 50-70% probability
of gusts in excess of 55 mph with a 60-80% probability primarily
across southeast portions of Fergus county. Hoenisch

&&

.AVIATION...
13/18Z TAF Period

VFR conditons will prevail at all terminals during this TAF Period
except for at the KCTB terminal. A weak cold front will move
through North-central Montana after 14/00Z and bring a line of
showers to the KGTF, KHVR, KHLN, and KLWT terminals. When this
line of showers moves through there is a 30% chance for
visibility to drop to MVFR-levels at the KGTF and KHVR terminals.
With that line of showers there is a 15% chance for an embedded
thunderstorm. There will be strong winds at the KEKS terminal for
the first 6 hours of this TAF period. Winds will increase at the
KHLN, KGTF, KLWT, KHVR, and KCTB terminals after 14/12Z. There
will be isolated instances of low-level wind shear between 14/03Z
and 14/18Z. -IG

&&

.FIRE WEATHER...
A Red Flag Warning remains in effect for portions of Southwest MT
through 9 PM this evening for low humidity and gusty winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  45  64  42  66 /  80  30  10   0
CTB  41  58  40  56 /  10  50  50  30
HLN  44  64  38  70 /  60  10   0   0
BZN  40  63  34  72 /  80  20   0   0
WYS  28  58  25  66 /  30   0   0   0
DLN  38  63  33  72 /  20   0   0   0
HVR  47  63  41  66 /  90  60  10  10
LWT  43  59  37  68 /  70  40  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Monday morning through Monday afternoon for
Fergus County below 4500ft-Judith Basin County and Judith Gap-
Snowy and Judith Mountains.

High Wind Warning until 6 PM MDT this evening for Madison River
Valley.

&&

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