921
FXUS65 KTFX 011109
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
509 AM MDT Tue Sep 1 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Marginal risk for severe thunderstorms over the plains of
   Central and North Central Montana today, with the primary risk
   being damaging winds.

 - Above normal temperatures today falling near to below normal
   for the remainder of the week.

 - Strong and gusty winds on Wednesday and Thursday, especially
   within the north-south orientated valleys of Southwest Montana.

&&

.DISCUSSION...
/Issued 1207 AM MDT Tue Sep 1 2026/

 - Meteorological Overview:

Longwave troughing over the Western CONUS, with south to southwest
flow aloft across the Northern Rockies, will dominate the upcoming
week. Shortwaves ejecting from the base of the trough axis and
lifting north to northeast within the aforementioned flow regime
will bring multiple opportunities for showers and thunderstorms to
Southwest through North Central Montana, most notably today and
Wednesday when the areal coverage precipitation will be greatest.
High temperatures, with the exception of today when highs will
generally be 5 to 10 degrees above normal, will mostly range from
near to below normal. Periods of strong and gusty winds will occur
over the next week, especially on Wednesday and Thursday within the
north-south orientated valleys of Southwest Montana where frequent
gusts in excess of 45 mph are likely to occur. - Moldan

- Forecast Confidence & Scenarios:

Strong Winds on Wednesday and Thursday...

ECMWF EFIs with respect to winds continue to support the potential
for an unusual to very unusual wind event, for early September,
through the period along and south of the I-90 corridor; most
notably within the Madison River Valley. Southerly H700 winds per
NAEFS analysis across Southwest Montana are prog`d to increase to
between 30-40kts by 18z Wednesday, and remain so through 00z Friday
before decreasing. These 2 to 2.5 standard deviation wind speeds
aligned with the north-south terrain in Southwest Montana,
specifically the Madison River Valley, combined with deep mixing
between 16z to 02z each day will support an ideal scenario for an
early season High Wind event. Given that NBM5.0 probabilities within
the Madison River for sustained wind speeds to exceed 40 mph range
between a 60-70% chance (Wednesday) and 30-40% chance (Thursday),
confidence remains high enough to continue the High Wind Watch with
this forecast package. The main reason for not upgrading the High
Wind Watch was uncertainty with respect to Wednesday night`s into
Thursday`s winds, which at this point in time appear to be slightly
weaker than during the daylight hours on Wednesday. Additionally, I
was unable to find a (6-9 hour) period in which wind speeds and/or
gusts decrease significantly enough in order to break-up the event
into two (2) distinct wind events, thus the watch from 18z Wednesday
through 03z Friday remains in effect for the Madison River Valley.

Listed below are the NBM5.0 probabilities for wind gusts to exceed
35, 45, and 55 mph for select locations across North Central,
Central, and Southwest Montana.

                    Wednesday`s Wind Gusts Probabilities
LOCATION               > 35 mph | > 45 mph | > 55 mph
Browning                  95%   |    50%   |     5%
Cut Bank                  95%   |    60%   |    15%
Havre                     80%   |    40%   |     5%
Great Falls               90%   |    60%   |    20%
Lewistown                 60%   |    10%   |    <5%
Helena                    80%   |    45%   |    15%
Bozeman                   90%   |    65%   |    15%
Dillon                    90%   |    70%   |    25%
Ennis                    100%   |    85%   |    30%
West Yellowstone          95%   |    60%   |     0%


                     Thursday`s Wind Gusts Probabilities
LOCATION               > 35 mph | > 45 mph | > 55 mph
Browning                  90%   |    65%   |    20%
Cut Bank                  90%   |    65%   |    20%
Havre                     75%   |    35%   |    <5%
Great Falls               80%   |    45%   |     5%
Lewistown                 70%   |     5%   |     0%
Helena                    75%   |    25%   |     0%
Bozeman                   85%   |    50%   |     5%
Dillon                   100%   |    60%   |    10%
Ennis                     95%   |    70%   |     5%
West Yellowstone          85%   |    40%   |     0%

Severe Thunderstorm Risk for Wednesday...

A marginal risk for severe thunderstorms, mainly capable of
producing damaging winds, exists on Wednesday along and northwest of
a Helena, to Monarch, to Winifred line. Showers and thunderstorms
lifting northeast from Idaho and Western Montana are expected to
overspread the aforementioned area through the afternoon hours, with
BUFKIT sounding depicting inverted-V`s beneath cloudbases of
10000kft. These high cloud bases combined with already anomalous low
level wind speeds will support the potential for a few severe
thunderstorm/shower wind gusts across portions of Central and North
Central Montana. - Moldan

&&

.AVIATION...
01/12Z TAF Period

Predominately VFR conditions will prevail throughout the 0112/0212
TAF period; however, scattered showers and thunderstorms
developing through the late morning hours and persisting through
the evening could bring brief periods of MVFR/low-VFR conditions
to the KHLN, KBZN, KEKS, and KWYS terminals. Areas along and south
of the I-90 corridor, particularly along the Idaho border, have
the highest chances of seeing showers through the morning hours
that would bring these MVFR/low-VFR conditions. Mountain
obscuration will largely be limited to where precipitation is
falling.

For KGTF: Light winds through 00z will yield a non-zero
chance for crosswinds to exceed 15kts. By 01z Tuesday the
potential for southeast wind gusts to exceed 15kts climbs to a 25%
chance, with these probabilities lingering through 05z before
winds turn to the southwest. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  85  56  81  48 /   0  10  50  20
CTB  83  52  77  45 /   0  10  70  50
HLN  86  51  78  48 /  10  40  60  10
BZN  82  49  77  45 /  20  40  20   0
WYS  69  37  64  33 /  40  60  20   0
DLN  81  45  74  42 /  30  50  60  10
HVR  88  54  87  49 /   0   0  50  60
LWT  83  54  82  48 /  10  10  30  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Wednesday afternoon through Thursday
evening for Madison River Valley.

&&

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