825
FXUS65 KMSO 010747
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
147 AM MDT Mon Sep 1 2025

.DISCUSSION...

KEY MESSAGES:

-  Isolated thunderstorms this afternoon and evening, mainly
   focused to NW Montana

-  Warming and drying trend into the weekend, potential heat
   impacts through Wednesday

A southwesterly flow is drawing a moist airmass into the region,
with atmospheric moisture measured at nearly 150% of normal for
this time of year. As temperatures soar to 10-15 degrees above
average this afternoon, this combination of heat and humidity,
along with a passing weak disturbance, will create enough
instability for isolated thunderstorms to develop. The highest
chances for these late afternoon and evening storms will be across
northwest Montana, particularly along the Continental Divide.
However, a stray storm cannot be ruled out elsewhere.

Through the middle of the week, the dominant ridge of high
pressure is forecast to strengthen and shift slightly westward.
This setup will effectively block moisture from the Pacific,
leading to a predominantly dry and hot weather pattern for most.
While valleys should remain dry, the intense daily heating could
still trigger a few isolated "pop-up" storms over the highest
mountain peaks each afternoon.

Both traditional and AI-based forecast models show high confidence
that the hot and mainly dry pattern will persist through the
workweek. A shift is expected to begin this weekend as the ridge
of high pressure finally moves eastward. This will open the door
for cooler, more seasonable temperatures to return, along with an
increasing chance for widespread showers and thunderstorms.

&&

.AVIATION...A very warm, moist, and hazy airmass remains in
place, with a weak disturbance providing the trigger for
convection mainly after 21z. Northwest Montana, especially along
the Continental Divide are the most likely areas for isolated
storms, but a few cells may also develop elsewhere. Smoke from
local wildfires will be a persistent factor for visibility. VFR
conditions are expected to prevail this morning, though visibility
may be restricted to MVFR in areas of smoke and haze,
particularly within valleys near active wildfires. Surface winds
will be predominantly easterly.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...Heat Advisory from noon today to 9 PM PDT Tuesday for Lower
     Hells Canyon/Salmon River Region...Orofino/Grangeville
     Region.

&&

$$