Considerable instability, anomalously high moisture content, and a weak disturbance led to several rounds of thunderstorms during the afternoon and evening.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS MSO wrote it up.
Considerable instability, anomalously high moisture content, and a weak disturbance led to several rounds of thunderstorms during the afternoon and evening.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Missoula, MT wrote its last area forecast discussion before the first event at Sep 10, 1:34 PM MST, 2 hours 26 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
234 PM MDT Wed Sep 10 2025
.DISCUSSION...
KEY MESSAGES:
- Flood watch for Idaho County this afternoon and evening due to
thunderstorms capable of heavy rainfall rates
- Thunderstorms each day through Friday featuring gusty outflow
winds and heavy rain, focused in the afternoon/evening hours
- Cooler and turning wet most areas Thursday night through
Saturday, with improving air quality
Spokes of moisture and energy will continue to rotate around the
broad scale upper level low currently centered over northern
California. The moisture values are 150 to 200 percent of normal.
As thunderstorms develop this afternoon and evening, rainfall
rates of 0.50" to 0.90" per hour will be feasible. A flood watch
has been issued for Idaho county, which is the main location being
favored by high resolutions models for thunderstorms activity this
evening. Flash flooding and debris flows on flood prone basins
and recent burn scars is possible (30-50 percent chance). If you
live near a recent burn scar make sure you have a way to receive
warnings and be prepared to head to higher ground! In addition to
locally heavy rain, gusty outflow winds to 40 mph are anticipated.
As the wave moves northwards, forecast models show convection
shifting into west-central and northwest Montana late this evening
into the overnight hours. Rainfall rates will likely taper off,
but gusty outflow winds and lightning may continue.
On Thursday, the focus of moisture shifts further east into
western Montana as the upper level low slowly shifts to the
northeast. That puts much of western Montana under the favored
location for thunderstorms, especially in the afternoon and
evening hours. Once again, gusty outflow winds and locally intense
rainfall will be the main concerns.
Thursday night into Friday is looking like a wetter period for
much of western Montana and north central Idaho. Forecast models
continue to favor a corridor from northcentral Idaho, north and
east through west-central and northwest Montana for widespread
rainfall. While total amounts still vary due to differences in
where the main low will track, probabilities for 0.50" or more is
still fairly high in these areas, around 50 to 70 percent.
Southwest Montana and Lemhi County will largely miss out on
additional rainfall with this event.
&&
.AVIATION...Showers and thunderstorms are expected to form across
southern portions of Idaho and Ravalli county by 10/2200z and
shift northwards through the evening hours. Storms capable of very
heavy rainfall rates and gusty outflow winds to 35kts are
anticipated, locally causing low visibility and obscuring the
terrain. KGIC, KHRF and KSMN are the most likely terminals to be
impacted through 11/000z, though showers and outflow winds may
reach KMSO and KGPI by 11/0300z and 11/0600z respectively.
Another round of thunderstorms is anticipated for Thursday,
particularly across western Montana.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...ID...Flood Watch until 9 PM PDT this evening for Lower Hells
Canyon/Salmon River Region...Orofino/Grangeville Region...
Southern Clearwater Mountains.
&&The Missoula radar (KMSX), 92 km away, was scanning. The volume nearest the first event began at 22:56 UTC.
1 thunderstorm wind. Local standard time, as filed.
Thunderstorm outflow winds marched northward through the Bitterroot Valley, resulting in about 20 utility customers losing power. General gusts were 35 to 45 mph topping out near 50 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2025Every state in 2025This day in weather historyWarnings in Montana, September 2025
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1287216.