Pulse convection and thunderstorms produced localized areas of nearly stationary, intense rainfall and hail ranging from pea sized to 1 inch in diameter during the afternoon and evening of September 11th.
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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.
Pulse convection and thunderstorms produced localized areas of nearly stationary, intense rainfall and hail ranging from pea sized to 1 inch in diameter during the afternoon and evening of September 11th.
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 11, 11:16 AM PST, 7 hours 5 minutes earlier.
Area Forecast Discussion National Weather Service Missoula MT 116 PM MDT Thu Sep 11 2025 .DISCUSSION... KEY MESSAGES: - Afternoon and evening showers and thunderstorms are expected today and Friday, bringing threats of gusty outflow winds up to 45 mph, localized heavy downpours, small hail, and frequent lightning. - A low-end debris flow threat continues for sensitive burn scars due to the potential for localized heavy rain. - An unsettled, cooler pattern persists through the weekend and into early next week, with another storm system expected to bring widespread showers and potentially much cooler temperatures by Monday. An upper-level low continues to spin slowly eastward across the Northern Rockies, keeping our region under a moist and unstable airmass. Convection allowing models agree on showers and thunderstorms developing by late this afternoon and continue into the evening. The primary concerns with today's storms will be gusty outflow winds, brief heavy rain, and lightning. With precipitable water values remaining high, some storms could produce localized rainfall rates that elevate the debris flow risk over susceptible burn scars, such as the Daly Burn scar. The potential for small hail also exists, particularly across north-central Idaho and southwest Montana, where instability in the hail growth zone is slightly higher, with CAPE values approaching 500 J/kg. The HRRR model suggests some of the stronger cells could produce hail up to penny size (0.75 inches). Storms will diminish by late in the evening. patchy fog may develop overnight in valleys that received significant rainfall. The slow-moving low will keep the region unsettled on Friday, with another round of scattered showers and thunderstorms expected. Model guidance suggests the focus for heavier showers may shift to northwest Montana and toward the mountains of Glacier National Park and the Salish Mountains. This could bring periods of heavy rain to the Going to the Sun Road. Threats of gusty winds and lightning will persist. By Friday night and into Saturday morning, partial clearing combined with moist ground could once again lead to patchy valley fog. By Saturday, the upper low finally shifts into eastern Montana. Our region will remain under cyclonic flow, supporting scattered showers and a few isolated thunderstorms, primarily across western Montana. Sunday may offer a brief lull with some morning sun before clouds increase ahead of our next approaching weather system. Confidence is increasing on another Pacific trough will move into the region Sunday afternoon into Monday, ushering in another round of widespread showers and cooler temperatures, and increased westerly winds. Ensemble model guidance presents two primary scenarios: A "cut-off" low (around a 70% probability): The trough deepens and slows down over the region. This would result in a wetter and colder period, with prolonged rainfall and valley high temperatures potentially struggling to get out of the 50s and low 60s on Monday. A progressive trough (around 30% probability): The system moves through more quickly without cutting off from the main jet stream. This would lead to a drier and breezier outcome with less overall precipitation. We will continue to monitor this system closely as it develops. For now, plan on a cool and wet start to the work week. && .AVIATION...Convective showers and thundershowers possible again this afternoon and evening between 11/2000z and 12/0400z. Spotty IFR/LIFR weather conditions expected with reduced visibilities and ceilings. Isolated areas of strong gusty outflow winds to 40 knots, heavy rainfall intensities that may cause ponding on runways and airfields, and small hail possible. The highest risk areas are most likely near KMSO, KHRF, and to a lesser extent KBTM and KGPI. Overnight patchy valley fog and lingering lowered ceilings/stratus are possible through about 12/1400z. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
Special Weather Statement
National Weather Service Missoula MT
643 PM MDT Thu Sep 11 2025
MTZ005-006-120115-
Bitterroot/Sapphire Mountains MT-Missoula/Bitterroot Valleys MT-
643 PM MDT Thu Sep 11 2025
...A strong thunderstorm will impact portions of north central
Ravalli County through 715 PM MDT...
At 642 PM MDT, Doppler radar was tracking a strong thunderstorm near
Hamilton, moving north at 10 mph.
HAZARD...Wind gusts up to 40 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Hamilton, Woodside, Pinesdale, Grantsdale, and Corvallis.
This includes Highway 93 S between mile markers 40 and 55.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4616 11407 4616 11430 4640 11433 4637 11399
TIME...MOT...LOC 0042Z 187DEG 8KT 4620 11422
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPHSpecial Weather Statement
National Weather Service Missoula MT
613 PM PDT Thu Sep 11 2025
IDZ006-120145-
Southern Clearwater Mountains ID-
613 PM PDT Thu Sep 11 2025
...A strong thunderstorm will impact portions of central Idaho County
through 645 PM PDT...
At 612 PM PDT, Doppler radar was tracking a strong thunderstorm 23
miles southeast of Lowell, or 37 miles east of Grangeville, moving
southwest at 5 mph.
HAZARD...Wind gusts up to 40 mph and Torrential rainfall.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Elk City.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 4599 11532 4575 11521 4567 11547 4586 11560
TIME...MOT...LOC 0112Z 055DEG 5KT 4586 11534
MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPHThe Missoula radar (KMSX), 180 km away, was scanning. The volume nearest the first event began at 02:17 UTC.
1 hail, 1 flash flood. Local standard time, as filed.
A hail size of one inch in diameter was reported 3 miles north-northwest of Kamiah by a trained spotter.
The Idaho County Sheriff's Office Facebook page reported washouts and subsequent closure on Reservation Line Road near Cottonwood Creek due to heavy rainfall from thunderstorms. A Flood Advisory for the area was issued on the evening of the 11th. The Sheriff's office reported that the road reopened by 1320 PST on the 12th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2025Every state in 2025This day in weather historyWarnings in Idaho, 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: 1295152, 1295742.