Flash Flood Warning 2, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
1221 PM MDT Thu Jul 31 2025

.DISCUSSION...

KEY MESSAGES:

- The KMSX Radar (Missoula, MT local weather radar) will remain
  offline due to scheduled maintenance through the first week of
  August.

- Flash Flood Watch in effect for this afternoon and evening for
  Lemhi and Idaho counties in Idaho and portions of western
  Montana.

- Widespread shower and thunderstorm activity continues Friday
  into Saturday, focusing across northwest Montana.

An anomalously high amount of moisture, coupled with an unstable
atmosphere, will lead to another round of widespread showers and
thunderstorms across western Montana and north-central Idaho this
afternoon and evening. A lack of shear and weak upper-level
steering winds will keep the primary threats from afternoon and
evening thunderstorms focused on heavy rain and frequent
lightning. A Flash Flood Watch will be in effect for Lemhi and
Idaho counties in Idaho, as well as for counties along and south
of Interstate 90 in western Montana. Flood-prone areas remain the
primary concern, including recent burn scars and regions of steep,
rocky terrain within the watch area. Instability will be
sufficient to support isolated strong to marginally severe
thunderstorms capable of producing wind gusts around 40–50 mph.
Isolated wet microbursts will also be a concern in western
Montana.

The focus of shower and thunderstorm activity will shift north of
I-90 by Friday afternoon and evening, as the upper-level low
slowly tracks farther north. Thunderstorms will once again be
capable of producing heavy rainfall, with Glacier National Park
standing out as a location to monitor closely in the coming days
for potential flash flooding. The NBM currently forecasts a
48-hour mean rainfall accumulation between 0.50" and 1.00" for
Lincoln and Flathead Counties from Friday through Saturday. The
probability of receiving 1 inch of rain is around 40–50 percent,
mainly concentrated along and north of Highway 2 in Lincoln
County.

A broad trough of low pressure will keep showers and thunderstorms
in the forecast through early next week. Cooler temperatures will
persist, with highs running 5-10°F below normal.

&&

.AVIATION... Easterly or northeasterly winds will prevail
throughout the day today, becoming gusty in the evening at KGPI.
Thunderstorm activity will once again increase this afternoon,
spreading from south to north. Gusty winds of 35-45 kts with
isolated 50 kt gusts, frequent lightning, and heavy rain will
accompany any storms that develop. Expect thunderstorm activity to
increase by around 31/2100Z at KSMN and KBTM. Storms should reach
KMSO by about 01/0000Z. Many of the high resolution model show
storms reaching northwest Montana late this evening. There is
around a 30% chance for thunderstorms to reach KGPI. Showers will
linger into the overnight, especially in north-central Idaho.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch from 3 PM this afternoon to 9 PM MDT this evening
     for Bitterroot/Sapphire Mountains...Butte/Blackfoot
     Region...Flathead/Mission Valleys...Kootenai/Cabinet
     Region...Lower Clark Fork Region...Missoula/Bitterroot
     Valleys...Potomac/Seeley Lake Region.

ID...Flood Watch from 2 PM this afternoon to 8 PM PDT this evening
     for Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region...Southern Clearwater Mountains.

     Flood Watch until 8 PM MDT this evening for Eastern Lemhi
     County...Western Lemhi County.

&&