Flash Flood Warning 1, NWS Missoula, MT

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.

&&

Preliminary Local Storm Report
National Weather Service Missoula MT
802 PM MDT Wed Jul 30 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0801 PM     Debris Flow      3 ENE Sula              45.85N 113.93W
07/30/2025                   Ravalli            MT   Park/Forest Srvc

            East Fork Bitterroot road closed due to
            debris flow.

&&

RNL