224
FXUS65 KTFX 210836
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
236 AM MDT Mon Sep 21 2026

.KEY MESSAGES...

 - Areas of fog this morning.

 - Mild and mainly dry conditions prevail through Thursday.

 - Pacific weather system brings windy and cooler conditions by the
   weekend

&&

.DISCUSSION...

 - Meteorological Overview:

An upper level ridge centered over MT and surface high pressure
over the northern US plains will maintain very light flow aloft and
at the surface across the region through tonight. Except for some
areas of fog this morning, primarily across the plains but also in
some SW MT valleys, mainly clear skies and light winds will prevail
with afternoon temperatures reaching the 70s. A southwesterly flow
develops Tuesday through the rest of the week, bringing some
additional warming with afternoon temperatures as much as 10-15
degrees above average through Thursday. A weakening upper level
disturbance tracking out of the Southwestern US across WY by mid-
week will bring risk for showers and perhaps an isolated thunderstorm
to portions of SW MT late Tue/Tue night. A larger scale upper
trough from the North Pacific begins to move onshore Friday with a
cold front sweeping east across the Northern Rockies and MT late
Friday or early Saturday. Gusty winds are likely to accompany and
follow the frontal system along with cooler temperatures by the
weekend.

 - Forecast Confidence & Scenarios:

Looking ahead to the late week/weekend system, there is reasonable
model agreement on a potent shortwave ejecting across the Northern
Rockies, which would favor a fairly energetic frontal passage and
associated winds. Probabilistic model guidance keeps the risk for
strong (>50mph) winds around 20% less, and there is still a fair
amount of timing uncertainty, but this will continue to be monitored
as the week progresses. Hoenisch.

&&

.AVIATION...
21/06Z TAF Period

Main concern overnight will be fog potential over mainly the
eastern half of the CWA. Fog is beginning to develop at 05z around
Lewistown. The fog should continue to develop overnight and spread
further east towards Havre/West Yellowstone and possibly as far
west as Helena. The fog could be dense at times with LIFR
conditions at times. Most of the fog should diminish by 17z Mon,
with generally quiet weather conditions expected Mon afternoon.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  79  48  80  49 /   0   0   0   0
CTB  76  44  77  47 /   0   0   0   0
HLN  76  45  77  49 /   0   0   0  10
BZN  73  41  75  45 /   0   0   0  10
WYS  67  30  68  34 /   0   0   0  30
DLN  72  41  73  42 /   0   0  10  20
HVR  79  46  80  49 /   0   0   0   0
LWT  75  44  79  48 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

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