Slow-moving thunderstorms brought torrential rainfall and triggered subsequent debris flows across parts of southwest Montana. The event was exacerbated by a deep layer of atmospheric moisture, with precipitable water values measured at nearly one inch, leading to highly efficient and impactful rainfall.
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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.
Slow-moving thunderstorms brought torrential rainfall and triggered subsequent debris flows across parts of southwest Montana. The event was exacerbated by a deep layer of atmospheric moisture, with precipitable water values measured at nearly one inch, leading to highly efficient and impactful rainfall.
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 Jul 30, 12:28 PM MST, 5 hours 2 minutes earlier.
Area Forecast Discussion
National Weather Service Missoula MT
128 PM MDT Wed Jul 30 2025
.DISCUSSION...
KEY MESSAGES:
- The KMSO Radar (Missoula, MT local weather radar) will remain
offline due to scheduled maintenance through the first week of
August.
- Flash Flood Watch in effect from 4-10PM MDT this evening for
Deer Lodge and Silver Bow Counties.
- Flash Flood Watch in effect for Thursday afternoon and evening
for Lemhi and Idaho Counties in Idaho and Ravalli County in
Montana.
- Widespread shower and thunderstorm activity continues Friday
into Saturday, focusing across northwest Montana.
GOES Water Vapor imagery this afternoon shows an upper level low
moving northeastward across western portions of the Great Basin,
with south-southwest flow transporting mid-upper level moisture
across the Northern Rockies. As discussed previously, high
pressure east of the Divide and a surface/thermal trough over the
Snake River Plane and eastern WA has maintained easterly winds
across the area, with gusts of 20-35 mph being felt across the
higher elevations and along the divide. Deeper moisture
originating from the High Plains continues to move east of the
Divide, with dew points climbing into the upper-40s to low-50s,
well above normal for this time of year. Given the anomalous
moisture in place, the stage is set for plenty of instability with
surface heating through this evening. High resolution guidance
suggests convection will initialize over central Idaho, before
tracking northeastward along the divide into southwest Montana
this evening. Light steering winds aloft increase the risk for
excessive rainfall and a flash flood watch has been issued for
Deer Lodge and Silver Bow Counties. High resolution guidance
suggests a higher risk (>30% probability) for 1-hr rainfall rates
in excess of 1.00 inch, given the likelihood for low-level east
winds to converge with south-southwest winds from convective
outflows. This convergence may allow for strong storms in the
vicinity of Butte and Anaconda, where flood prone areas exist.
Easterly winds will ramp up this evening across western Montana
as the pressure gradient tightens. A lake wind advisory remains in
effect this evening for Flathead Lake, where easterly gusts will
reach 25-35 mph.
On Thursday, the aforementioned upper level low will move
northward into central Idaho, with widespread showers and
thunderstorms expected to develop across central Idaho and western
Montana. A flash flood watch has been issued across Lemhi, Idaho,
and Ravalli Counties, where anomalously high moisture,
instability, and light storm steering winds will increase the risk
for flash flooding. Flood prone areas remain the primary concern,
including recent burn scars, and areas of steep rocky terrain,
such as the Salmon River corridor and US Highway 95 north of
Riggins, Idaho. Given high instability (1500-2000 J/kg) in place,
a few strong to marginal severe thunderstorms are expected. With a
lack of wind shear, these storms will be of the pulse variety and
may produce localized severe winds with wet microbursts being a
concern.
The focus of shower and thunderstorm activity will move north of
I-90 Friday into Saturday as the upper level low slowly spins
towards the USA-Canada border. Thunderstorms will once again be
capable of producing heavy rain, with Glacier Park standing out as
an area to be monitored closely in the coming days for any flash
flooding concerns.
A broad trough of low pressure will keep showers and thunderstorms
in the forecast through early next week. Cooler temperatures will
continue, with highs running 5-10F below normal.
&&
.AVIATION...Northeast to east winds will be present at terminals
into Thursday morning. A sharp increase in gusts is expected
between 31/0000z and 31/0400z with gusts 15 to 30 kts at times.
Disorganized convection will affect the Northern Rockies this
afternoon with outflow winds helping to develop convection from
south to north, mainly in the mountains but occasional in the
valleys. Thunderstorms outflow gusts of 30-40 mph may be an
initial concern followed by moderate to locally heavy rainfall.
The best chances for showers and thunderstorms will be in the
vicinity of KSMN, KBTM, and KHRF. Activity at other terminals is a
lower probability but cannot be ruled out. Any shower or
thunderstorm will be capable of briefly (30-45 minutes) degrading
visibility to 4SM. Convective activity will diminish by late
evening as daytime heating is lost.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch from Thursday afternoon through Thursday evening for
Bitterroot/Sapphire Mountains...Missoula/Bitterroot Valleys.
Lake Wind Advisory from 6 PM to 11 PM MDT this evening for
Flathead/Mission Valleys.
Flood Watch from 4 PM this afternoon to 10 PM MDT this evening
for Butte/Blackfoot Region.
ID...Flood Watch from Thursday afternoon through Thursday evening for
Lower Hells Canyon/Salmon River Region...
Orofino/Grangeville Region...Southern Clearwater Mountains.
Flood Watch from Thursday afternoon through Thursday evening for
Eastern Lemhi County...Western Lemhi County.
&&The national radar mosaic for the moment the first event began.
1 debris flow, 1 heavy rain. Local standard time, as filed.
Radar-estimated rainfall of 1.77 inches fell in one and a half hours and triggered a debris flow that covered the East Fork Road, east of Sula, at Mile-marker 4.
Radar estimated 1.41 inches of rain had fallen over the western portion of the Daly burn scar, located west of Skalkaho Pass. A few days later, a rock slide was reported in the vicinity.
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, July 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 2026-10-01. Each event’s entry at NCEI: 1286097, 1286094.