602
FXUS65 KTFX 212358
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
558 PM MDT Fri Aug 21 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Scattered showers and thunderstorms, a few of which may be
   severe, Saturday and Sunday.

 - Elevated fire weather conditions Sunday as breezy winds develop
   in most areas behind a front.

 - On the warmer side of average next week with scattered showers
   and thunderstorms most days.

&&

.DISCUSSION...
/Issued 138 PM MDT Fri Aug 21 2026/

 - Meteorological Overview:

The ridge axis associated with a high amplitude upper level ridge
across the Northern Rockies will begin shifting east of the area
late tonight and into the morning Saturday. This will eventually
result in a southwesterly flow aloft which will foster scattered
showers and thunderstorms this weekend ahead of a cold front. In the
meantime the remainder of the afternoon looks dry and warm. A few
showers or thunderstorms cannot be ruled out this evening along the
Continental Divide in Southwest Montana, but those probabilities are
low.

Flow aloft into tomorrow has a much more southerly component than
westerly, at least initially, which will aid in advecting in
monsoonal moisture. Combine this with ample flow and forcing
aloft from an approaching trough across the Pacific NW and
scattered afternoon and evening thunderstorms will develop as a
result. There looks to be enough of a balance between drier
inverted-V lower level profiles and ample moisture aloft to result
in both a gusty wind and excessive rainfall risk Saturday
afternoon and evening. Forcing associated with the approaching
upper level trough from the Pacific NW will keep at least widely
scattered showers and thunderstorms around through the overnight
Saturday into Sunday morning.

Heading into Sunday the core of the upper level disturbance passes
just north of the region, which will foster both a thunderstorm
threat and fire weather threat. The magnitude and duration of each
of these threats will be dictated by just how quickly an associated
cold front moves through.

Heading into next week Monday looks to be a slightly cooler day
behind a front, but temperatures quickly trend back warmer by
Tuesday. Persistent southwesterly flow aloft will keep at least
isolated showers and thunderstorms in the forecast through next
week. -AM

 - Forecast Confidence & Scenarios:

Thunderstorms Saturday:

There is still a bit of a north-south discrepancy with respect to
where showers and thunderstorms develop through the day. Given
precipitable water values near or in excess of an inch, wherever
these thunderstorms develop will have the risk for at least briefly
heavy rain. Areas of greatest concern for localized flash flooding
will be in urban areas and over and near burn scars. The threat for
gusty winds will also be around, with a few gusts in excess of 58
mph not out of the question.

Sundays fire weather and thunderstorm risk:

A quicker front would increase the duration of winds and related
fire weather concerns, while a slower front would allow for greater
instability to form and result in a greater thunderstorm risk. The
kinematic environment for thunderstorms ahead of the front would be
sufficient for a few organized thunderstorms, including a supercell
or two, capable of gusty winds and hail. -AM

&&

.AVIATION...
22/00Z TAF Period

Predominantly VFR conditions across the region with some mild
slant range visiblity reductions due to smoke in Southwest MT.
Isolated showers and thunderstorms are expected over far Southwest
MT late this evening from 03Z to 09Z however there is still
uncertainty on rain intensity. Wind gusts of up to 35 KT and
cloud-to-ground lightning will be the primary threats with these
storms. A low chance of potential non-thunderstorm wind shear for
KBZN from 03Z to 05Z is also a threat. The next round of more
widespread and stronger thunderstorms will be Saturday afternoon
after 22/21Z impacting most terminals in Southwest and Central MT
with localized heavy rainfall being a greater threat for those.


For KGTF: VFR conditions will prevail in this TAF period. Winds
will be generally light out of the East. There is a 30% chance
for thunderstorms Saturday after 22/23Z until late Saturday night
which could create gusty outflows of up to 35 KT as well as
localized heavy rain and lightning.
- Akins

&&

.FIRE WEATHER...

The fire weather concerns begin when isolated showers and storms
with cloud to ground lightning and little precipitation pass
through this evening into tonight. Even though this activity will
be isolated, some new fire starts can`t be ruled out. More
productive storms move in on Saturday, but again the presence of
cloud to ground lightning may ignite new fire starts. The most
concerning day will be on Sunday when a surface front brings
gusty westerly winds amid continued very warm and dry conditions.
The timing of this front will ultimately determine how long the
dry windy conditions persist. The latest NBM probabilistic
guidance highlights large areas of north-central and portions of
southwest Montana with over a 60% chance for wind gusts over 30
mph. Although the fuels aren`t quite as dry as they were in
earlier in the month, elevated fire conditions will be present and
the wind may be enough to ignite any lightning caused hold over
fires from Friday and Saturday`s storms. - RCG

&&

.HYDROLOGY...

The combination of increased monsoonal moisture from the south  and
better surface Tds working in near the surface from the east will
result in the risk for heavy rainfall from thunderstorms Saturday.
Should confidence rise in these heavier thunderstorms occurring over
a particular burn scar or urban area, a flash flood watch may become
necessary. The better moisture begins to exit Sunday, which will
close the window for the potential for excessive rainfall for the
near term. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  92  62  91 /  10  20  20  20
CTB  55  86  57  82 /  10  20  20  20
HLN  61  91  58  88 /  20  40  40  30
BZN  59  88  54  87 /  20  30  50  30
WYS  52  81  46  79 /  20  30  40  30
DLN  58  86  52  85 /  30  40  40  20
HVR  60  94  62  94 /   0  10  10  20
LWT  58  89  59  90 /  10  20  20  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

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