189
FXUS65 KMSO 271832
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1232 PM MDT Wed Aug 27 2025

.DISCUSSION...

KEY MESSAGES:

-  Degraded but slowly improving air quality due to wildfire
   smoke continues, mainly across central Idaho.

-  Potential for flash flooding due to heavy rainfall from slow-
   moving thunderstorms through tonight

A potent low-pressure system is spreading soaking rain across the
region today, fueled by a near-record amount of atmospheric
moisture. This morning`s upper-air sounding from Boise measured
1.57 inches of precipitable water, the second-highest value on
record for the date since 1948.

This abundance of moisture, combined with lift from the low and
instability from daytime heating, will generate intense showers
and thunderstorms. These storms are capable of producing rainfall
rates up to 1 inch per hour, creating a threat of flash flooding,
rockslides, and debris flows.

Primary Hazards and Areas of Concern:

The primary threats today are flash flooding and debris flows,
particularly in steep terrain, on Forest Service roads, and over
recent burn scars.

Locations with the highest probability for runoff issues include:

 - Highway 95 from Riggins to White Bird in Idaho

 - Skalkaho and East Fork Roads in the Sapphire Range of Montana

 - Highway 93 south of Salmon, Idaho

Backcountry travel is strongly discouraged this afternoon through
tonight due to the potential for hazardous conditions.

Forecast Timeline:

Tonight through Thursday: Rain will push northward overnight,
leading to widespread showers across west-central Montana by
Thursday morning. By Thursday afternoon, showers and thunderstorms
will develop over northwest Montana. Expect below-average high
temperatures across the region.

Friday & the Weekend: The storm system will exit on Friday,
allowing for a warming trend. Temperatures will quickly return to
normal, though a few afternoon showers and thunderstorms will
still be possible. Saturday and Sunday will be even warmer and
drier under a northwesterly flow, with isolated shower chances,
mainly along the Continental Divide.

Early Next Week: Forecast confidence decreases starting Monday.
Models show significant disagreement on the track and timing of
the next approaching low-pressure system, making for an uncertain
start to the week.

&&

.AVIATION...Scattered showers and isolated thunderstorms will
continue to slowly spread from south to north over north-central
Idaho and western Montana through Thursday. Locations with the
highest probability (25-35%) for thunderstorms, will be KSMN, KBTM
and KHRF. Brief heavy rainfall and occasional lightning will be
the main threats. Precipitation will be more widespread Thursday.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through this evening for Bitterroot/Sapphire
     Mountains...Missoula/Bitterroot Valleys.

ID...Flood Watch through this evening for Eastern Lemhi County...
     Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region...Southern Clearwater
     Mountains...Western Lemhi County.

&&

$$