578
FXUS65 KTFX 221120
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
520 AM MDT Wed Jul 22 2026

Aviation Section Updated.

.KEY MESSAGES...

- Daily chances for afternoon showers and thunderstorms through
  Friday.

- Scattered to numerous thunderstorms in Southwest Montana on
  Wednesday have the potential to produce heavy rain and localized
  flash flooding.

- Temperatures will warm up into the upper 90s to mid 100s through
  the weekend with the warmest temperatures expected on Friday
  and Saturday.

&&

.DISCUSSION...
/Issued 1203 AM MDT Wed Jul 22 2026/

 - Meteorological Overview:

A shortwave will move up from the southwest today bringing a chance
for showers and thunderstorms primarily south of the I-90 corridor.
Combined with the monsoonal moisture in the area and a lack of
steering flow there is an increased potential for localized flash
flooding in the higher terrain of Southwest Montana (see the
HYDROLOGY section for more detail).

Another weak shortwave moves through the area on Thursday with
another round of afternoon showers and thunderstorms possible, this
time extending further north towards the Hi-Line but with a lower
chance for heavy rain compared to Wednesday.

Heading towards the weekend the upper-level ridge starts to build
over the Intermountain West leading to well above normal
temperatures across much of the region, especially along the
Northern Plains. Dry air will start advecting along an upper-level
jet streak from the west which will both bring lower relative
humidity values and the potential for gusty winds to the region. The
potential combination of hot, dry, and windy conditions will lead to
elevated fire weather concerns through at least the weekend (see the
FIRE WEATHER section for more detail).

An fast moving upper-level trough will push through on Sunday which
will help to moderate temperatures back down into the 90s for early
next week but with the upper-level ridge potentially building back
towards the middle of next week chances remain high that above
normal temperatures will continue at least through the remainder of
July.


 - Forecast Confidence & Scenarios:

Thunderstorms Wednesday: Tall, skinny CAPE and PWATs exceeding 1.25"
in the model soundings confirm the potential flash flood risk across
Southwest Montana. When evaluating the current Flash Flood Watch,
there still is not enough confidence to extend it to the lower
elevations. There may be some localized heavy rainfall in the
valleys of Southwest Montana but the higher confidence and concern
is still in the mountainous areas of Beaverhead, Madison, and
Gallatin counties.

As for the Horse Gulch burn scar, the models are still very
uncertain on whether showers/thunderstorms will make it that far
north so for now that area will be left out of the watch. But it
will be something to keep an eye on as the day progresses.

Beyond the heavy rainfall there are some hints in the models that a
couple storms may become strong to severe, particularly along the
Idaho/Montana border. Hail would be the primary threat and if a
heavy rain plus accumulating small hail scenario were to develop it
could enhance the flash flood concerns already present in the
mountains. Overall the severe threat remains marginal but it is
something that folks should be aware of as the afternoon progresses,
especially those who might be recreating in the backcountry.


Thunderstorms Thursday: Hi-res model guidance shows CAPE in the 1000-
2000 J/kg range across a good portion of the region with generally
little cap and modest lapse rates which all suggests the potential
for thunderstorm development in the afternoon. What will be
noticeably lacking on Thursday is shear. So thunderstorms could
potentially develop but it might be a lot more sporadic and popcorn
in nature. With DCAPE values as high as they are there is naturally
a chance for some gusty winds with any thunderstorm that develops.
But otherwise Thursday afternoon feels pretty conditional and there
is still a lot that needs to be resolved in the models to increase
confidence in some of the higher-end threats.


Heat Friday thru Sunday: Across much of the US-87 corridor from
Great Falls to Havre, the US-2 corridor east of Rudyard and along
the Upper Missouri River Breaks there is a greater than 60% chance
for 100+ degree temperatures on Friday. On Saturday, the risk for
100+ expands to include much of the the Northern Plains with a 60%
chance for 100+ temperatures along the 287 corridor between Helena
and Three Forks. 20-30% probabilities stick around on Sunday but
beyond that temperatures start to moderate back down into the 90s
early next week.

Heat-related impacts will be a big concern this weekend. Right now
the highest concerns are in Hill, Blaine, Chouteau, and Fergus
counties with surrounding areas having more moderate concerns as
locations further west will at least be able to cool down a couple
more degrees overnight compared to those locations further east.
Heat-related illness will be a concern for those recreating and
spending an extended amount of time outdoors and anyone without air
conditioning. In particular, vulnerable populations and those most
likely to experience heat-related illness will be at an even higher
risk through the three day period.

While the worst of the heat is expected to be over after Sunday, it
may be a while before a true cool down is expected as long-range
models suggest the upper-level ridge could persist through next
week. Therefore, those who are the most sensitive to the heat should
be on the lookout for compounding heat stress, especially if they
are without air conditioning or unable to find a cool location to
recover. -thor

&&

.AVIATION...
22/12Z TAF Period

Monsoon moisture will continue to stream in from the
west/southwest and bring variable cloudiness and scattered to
numerous showers and thunderstorms, mostly over central and
southwest MT. A subtle shortwave moves in and brings a more
concentrated brand of showers and thunderstorms over southwest and
portions of central MT between 22/18 and 23/06Z. The primary
concern with this activity will be heavy downpours, lightning,
and gusty/erratic winds. MVFR and even lower flight categories
will be present beneath showers and storms. Low stratus and patchy
fog looks to develop near KBZN and KWYS after 23/06Z. KWYS will
be most susceptible to IFR/LIFR conditions. - RCG

&&

.FIRE WEATHER...

Hot, dry, and windy conditions are expected through the weekend
which will lead to elevated fire weather concerns across much of the
region. The main limiting factor will be the potential for wetter
showers and thunderstorms both Wednesday and Thursday.

There is a concern that most of the wetter showers will not make it
north of a line between Helena and White Sulphur Springs which would
put North-Central Montana at a much higher risk for elevated fire
weather conditions through the weekend. Additionally, if the wetter
storms on Wednesday and Thursday are unable to materialize, or they
are a lot more isolated than what is currently expected, then that
could also elevate fire weather concerns for Central and Southwest
Montana.

As it stands there is a generalized concern for elevated fire
weather conditions starting on Friday but much of the threat will
not be determined until Thursday evening when it becomes clear which
locations were able to pick up some wetting rain ahead of the
incoming hot, dry, and windy conditions.  -thor

&&

.HYDROLOGY...

On Wednesday the Weather Prediction Center (WPC) has issued a
Slight Risk (15% chance for flash flooding within 25 miles of a
point) for flash flooding across most of Southwestern Montana.
Between the I-90 corridor and a line between Augusta to Great
Falls to Lewistown WPC has issued a Marginal Risk (5% chance for
flash flooding within 25 miles of a point)for flash flooding on
Wednesday. In addition across the mountains of Southwestern
Montana there is a 50 - 70% chance for rainfall rates in excess of
one half inch per hour on Wednesday. In addition there is around
a 50% chance for rainfall rates in excess of three quarter of an
inch per hour across the mountains of Southwestern Montana on
Wednesday. There is a 20 - 40% chance for an inch of rain or
greater across the mountains of Southwestern Montana on Wednesday.
As a result a Flash Flood Watch was issued for the mountains
south of I-90 from Noon to Midnight on Wednesday. -IG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  90  62  96  63 /   0  10  10  20
CTB  87  58  94  62 /   0  10  10  10
HLN  90  63  93  63 /  30  30  20  10
BZN  90  59  92  60 /  50  50  20  20
WYS  82  51  82  50 /  80  70  50  10
DLN  85  56  88  57 /  70  60  20  10
HVR  92  60 100  65 /   0   0  10  10
LWT  86  57  91  60 /  10  10  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from noon MDT today through this evening for
Gallatin and Madison County Mountains and Centennial Mountains-
Northwest Beaverhead County-Ruby Mountains and Southern
Beaverhead Mountains.

&&

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