417
FXUS65 KTFX 201408
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
808 AM MDT Wed Aug 20 2025

.KEY MESSAGES...

 - Warm today with a chance for scattered showers and
   thunderstorms in the afternoon and evening.

 - Cooler and more seasonable temperatures expected Thursday
   through the weekend.


&&

.UPDATE...

The morning update has been published. An unstable southwesterly
flow aloft will bring another round of showers and thunderstorms
this afternoon into tonight, mostly for locations east of I15. The
strongest activity is expected over Central/North-central
Montana, particularly for Hill/Blaine counties southward into
Fergus and Judith Basin. The primary thunderstorm hazards will be
localized strong, gusty winds, hail, and brief downpours in
addition to lightning.

The high fire risk continues today over Southwest Montana and
there was some consideration given to adding some of our fire
weather zones over and south of the Big Belt Mountains to the red
flag warning, but declined to do so given the strongest winds and
highest isolated dry thunder risk looks to mostly remain south of
I90. With that being said, the elevated threat for new fire
starts from lightning and or gusty winds remains for almost
anywhere in the forecast area. A cold frontal passage tonight
will bring cooler temperatures and much less thunderstorm
activity heading into the weekend. - RCG

&&

.DISCUSSION...
/Issued 305 AM MDT Wed Aug 20 2025/

 - Meteorological Overview:

The upper level ridge will start to break down this afternoon and
evening as a trough moves through across central and southern
Canada. An associated cold front will make its way across the
region allowing for scattered showers and thunderstorms through
the late evening hours. Similar to previous days, the main
concerns will be gusty, erratic winds and lightning with small
hail being a secondary threat today.

Behind the cold front, cooler and more seasonable temperatures
will persist through the weekend. An upper level ridge will start
to build over the western CONUS which will bring northwesterly
flow to the region and, depending on exactly where the ridge sets
up, may bring a chance for afternoon showers and thunderstorms to
the region, particularly across southwestern Montana.


 - Forecast Confidence & Scenarios:

Regarding thunderstorms this afternoon, there is still some
lingering uncertainty as to how exactly this event will play out.
The NBM remains very dry while hi-res guidance brings in the first
showers and thunderstorms along the Montana/Idaho border as early
as 10 AM to 12 PM in some cases and slowly spreading northward
while precipitation coverages also fill in along the Hi-Line as
the cold front approaches. The concern, particularly across
southwestern Montana, will be how dry these thunderstorms end up
being. Model soundings have pointed to drier thunderstorms south
of the I-90 corridor with increasing PWATs. A mix of wet and dry
thunderstorms is expected across central and north-central Montana
which may bring some localized heavier rain but otherwise these
storms are expected to bring little in the way of accumulation.
Rather instead gusty, erratic winds and more lightning is expected
which will be a concern for fire weather concerns.  -thor


&&

.AVIATION...
20/12z TAF Period

Lingering SHRA across the area this morning will dissipate by 15z,
but should not bring impacts to terminals aside from some
downdrafts and LLWS near the showers. While winds will be light
early today, expect gusts to 25kts or so across the plains by the
mid to late afternoon. Another round of SHRA and TSRA will develop
during the late afternoon and evening hours today. While any
terminal could be impacted from these SHRA/TSRA and their
outflows, the most likely terminals to see these are from KGTF
and KLWT points south. Ludwig

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.FIRE WEATHER...

Critical fire weather concerns are expected this afternoon across
portions of southwest Montana with highs in the upper 80s to low
90s, minimum RH values as low as 12%, winds gusting up to 30 mph,
and the potential for dry thunderstorms in the afternoon.

Elevated fire weather concerns are expected across the remainder
of the region with highs across the plains reaching up into the
low 90s, minimum RH values in the upper teens to low 20s, winds
gusting up to 20 mph, and a chance for thunderstorms in the late
afternoon through the evening.

A cold front will pass through this afternoon into Thursday which
will allow for temperatures to cool down and allow for better
overnight recovery heading into Thursday and Friday which will, at
least temporarily, ease some of the worst concerns.  -thor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  92  54  80  53 /  20  30   0   0
CTB  85  48  76  47 /  20   0   0   0
HLN  91  56  84  52 /  30  40   0   0
BZN  93  51  86  48 /  20  30   0   0
WYS  86  40  83  39 /  20  20   0   0
DLN  90  48  83  47 /  20  20   0   0
HVR  92  53  78  49 /  30  40   0   0
LWT  86  53  76  51 /  20  50   0   0

&&

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

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