918
FXUS65 KTFX 130931
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
331 AM MDT Thu Aug 13 2026

.KEY MESSAGES...

- Cooler temperatures persist across the region through the end
  of the week with showers and thunderstorms around at times.

- A few thunderstorms will be capable of producing heavy rain,
  which would be impactful if they were to move over a city or
  burn scar.

- Temperatures trend closer to normal by the end of the weekend,
  with continued opportunities for afternoon and evening showers
  and thunderstorms.

&&

.DISCUSSION...

Meteorological Overview:

A southwesterly flow aloft will more or less persist across the
Northern Rockies through the weekend into early next week. This flow
is initially more cyclonic in nature, which will foster plenty of
showers and thunderstorms through Friday evening across the region.
Persistent surface winds from the east and northeast will continue
to usher in cooler temperatures. Precipitable water values will tick
a touch higher today, resulting in increased precipitation
efficiency with showers and thunderstorms that develop. The most
robust thunderstorms that develop over the next few days will be
capable of producing at least briefly heavy rainfall. Should one of
these stronger storms move over urban areas or burn scars, some
localized flash flooding cannot be ruled out. Lightning and gusty
winds will also be a concern with stronger thunderstorms.

Heading into the weekend the nature of the southwesterly flow aloft
becomes a bit more anti-cyclonic. That said, moisture working in
from the southwest will combine with temperatures trending closer to
normal to result in scattered afternoon showers and thunderstorms.

Greater uncertainty in the pattern develops toward the middle of
next week. At this point the main takeaway will be for scattered
showers and thunderstorms most days with temperatures near average.
-AM

- Forecast Confidence & Scenarios:

Flash flooding concerns:

HREF 10km neighborhood probabilities for a quarter of an inch of
rain over an hour is at or greater than 50% over the Pioneer
Mountains today. Given the recent intense fire activity resulting in
hydrophobic soils and steep terrain within the fire footprint, it
will not take much precipitation over a short period to result in
some flash flooding. As such, this area was added to a Flash Flood
Watch valid for this afternoon and evening. Another Flash Flood
Watch may be necessary for the same area for tomorrow as well.
Ongoing Flash Flood Watch for the Horse Gulch Burn Scar remains in
effect unchanged from the previous forecast update.

Risk for strong thunderstorms:

While inverted-V soundings will be around across SW MT the next two
days, these inverted-Vs are rather shallow all things considered.
This will help reduce the risk for a strong to severe gust. At this
time the main concern will continue to be lightning, aside from
briefly heavy rainfall. -AM

&&

.AVIATION...
13/12Z TAF Period

Scattered showers/thunderstorms will affect the CWA through the
period. The main impact from any storms will be lightning, brief
heavy rainfall and gusty winds. The combination of
thunderstorms/smoke will continue to obscure mountains across the
CWA through the period.

For KGTF: Surface winds will generally remain out of the
northeast, and generally less than 15 knots through the period.
Some higher gusts are possible in/near thunderstorms. At this
time, the forecast models all have different timing of when the
storms will hit, thus confidence is low at this time exactly when
a gusty wind is possible from a stronger storm. Brusda

&&

.HYDROLOGY...
Precipitable water values will continue be around an inch or
so across the region the next couple days. This will allow for the
most robust thunderstorms to produce at least briefly heavy
rainfall. Should these thunderstorms move over sensitive areas such
as urban areas, burn scars, or active fires, excessive rainfall
leading to flash flooding will be possible. A Flash Flood Watch is
in effect for the Horse Gulch burn scar. The Flash Flood Watch
was also expanded to include the Pioneer Mountains, where steep
terrain and hydrophobic soils will need very low total rainfall
amounts to result in flash flooding. -AM/Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  67  49  64  48 /  80  90  60  40
CTB  57  43  60  43 /  90  80  40  20
HLN  71  52  68  51 /  30  80  70  50
BZN  76  49  70  47 /  40  90  90  80
WYS  71  38  66  35 /  70  70  70  80
DLN  75  48  70  45 /  70  90  90  70
HVR  65  47  68  46 /  90  60  20  40
LWT  66  47  64  45 /  70  80  80  70

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Flash Flood Watch this evening for the Horse Gulch burn scar.

Flash Flood Watch from 1 PM MDT this afternoon through this
evening for the Pioneer Mountains burn scar in Beaverhead County.

&&

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