Montana, 2021Flash Flood and Wildfire in Montana, August 1, 2021
August 1, 2021 · NWS MSO · 2 events in 2 counties and zones
Monsoonal subtropical moisture set the stage for thunderstorms to produce heavy rainfall across southwest Montana. North of this moisture plume, the Boulder 2700 fire burned down structures near Montana Highway 35 along the southeastern shore of Flathead Lake.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
- Tornadoes
- Tropical storms and surge
- Floods
- Wind
- Hail
- Winter weather
- Heat and drought
- Cold
- Fire, smoke and dust
- Marine and coastal
- Other
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- Deaths
- 0
- Injuries
- 0
- Property damage
- $3.6 million
- Crop damage
- None recorded
- Events
- 2
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.
Monsoonal subtropical moisture set the stage for thunderstorms to produce heavy rainfall across southwest Montana. North of this moisture plume, the Boulder 2700 fire burned down structures near Montana Highway 35 along the southeastern shore of Flathead Lake.
What forecasters said that day
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 31, 2:29 PM MST, 9 hours 31 minutes earlier.
Area forecast discussion, Jul 31, 2:29 PM MST, 9 hours 31 minutes before
Area Forecast Discussion
National Weather Service Missoula MT
329 PM MDT Sat Jul 31 2021
...FLASH FLOODING POSSIBLE ACROSS LEMHI AND IDAHO COUNTIES
TODAY...
...FLASH FLOODING POSSIBLE ACROSS MOST OF CENTRAL IDAHO AND
WESTERN MONTANA ON SUNDAY AFTERNOON AND EVENING...
.DISCUSSION...An impressive surge of monsoon moisture is moving
into the region. The first disturbance on the leading edge of the
monsoon moisture will pass through Lemhi County and southern
Idaho County through this evening, which will produce
thunderstorms. Some of the storms will be capable of heavy rain,
so the flash flood watch remains in effect.
Near record atmospheric moisture will advect into most of central
Idaho and western Montana on Sunday and Monday. Another
disturbance is forecast to arrive during Sunday afternoon and
cause heavy rain producing thunderstorms that will track from
south to north. Flash flooding is a concern with Sunday's
thunderstorms, so the flash flood watch has been expanded to
include, Clearwater, Ravalli, Granite, Missoula, Mineral,
Sanders, and Lake counties. Radar projections also show gusty
winds develop ahead of the thunderstorms in northwest Montana, so
wind gusts of 40-50 mph are possible.
A more organized shortwave trough will cause another round of
heavy rain producing thunderstorms on Monday. The main storm
focus will be in west central and southwest Montana, that may
prompt additional flash flood watches.
After a couple of active weather days, Tuesday and Wednesday
should be more stable with only isolated storms.
Another weather system is possible on Thursday and Friday with
widespread showers and thunderstorms.
&&
.AVIATION...A thermal low pressure across the Columbia Basin will
continue to produce easterly winds across much of the Northern
Rockies airspace. Wind gusts of 15-20 knots will be common through
to 01/0600Z. Models suggest area wildfire smoke will shift
westward across central Idaho and eastern Washington, with
visibility improvements expected across western Montana. Scattered
showers and thunderstorms across Lemhi and Idaho counties through
at least 01/0600Z, but latest projections show storms in Idaho
County for most of the night. Thunderstorms through tonight will
be capable of producing heavy rainfall (with visibility
reductions below 5SM likely under storm cores) and gusty erratic
outflow winds up to 35 knots. The next round of heavy rain
producing storms are expected in much of central Idaho and western
Montana beginning Sunday afternoon, with gusty outflow winds over
40 knots near storms.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT... Flash Flood Watch from Sunday afternoon through Sunday evening
Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...
Flathead/Mission Valleys...Kootenai/Cabinet Region...Lower
Clark Fork Region...Missoula/Bitterroot Valleys...
Potomac/Seeley Lake Region...West Glacier Region.
Heat Advisory until 9 PM MDT this evening Kootenai/Cabinet
Region...Lower Clark Fork Region.
ID...Flash Flood Watch through Sunday evening Eastern Lemhi County...
Lower Hells Canyon/Salmon River Region...Southern
Clearwater Mountains...Western Lemhi County.
Flash Flood Watch from Sunday morning through Sunday evening
Northern Clearwater Mountains...Orofino/Grangeville Region.
Heat Advisory until 8 PM PDT this evening Lower Hells
Canyon/Salmon River Region...Northern Clearwater
Mountains...Orofino/Grangeville Region...Southern
Clearwater Mountains.
&&Wildfire, Flathead/Mission Valleys
- When
- August 1, 12:00 AM MST to 12:00 PM MST
- Where
- Flathead/Mission Valleys forecast zone
- Property damage
- $3.6 million
- Reported by
- Fire Department/Rescue
- Coordinates
- 47.872, -114.424 (the zone’s center; the record gives no point)
The Boulder 2700 fire spread quickly during the early morning hours of August 1st in the presence of strong downslope winds and dry conditions. The fire ran down the west slope of the Mission Mountains, crossing Montana Highway 35, reaching the east shore of Flathead Lake. Damage surveys confirmed the loss of 14 primary structures and 17 outbuildings.
Flash Flood, Silver Bow
- When
- August 1, 6:49 PM MST to 7:30 PM MST
- Where
- Silver Bow County, 1.08 mi WSW of Walkerville to 0.25 mi WNW of Butte
- Cause
- Heavy Rain
- Reported by
- Law Enforcement
- Coordinates
- 46.025, -112.551
Law enforcement reported heavy rainfall led to street flooding in the Uptown District of Butte, Montana. Further, road department officials reported several clogged storm drains resulted in areas of minor street flooding.
- Wildfire
- A fire burning in wildland vegetation, with its acreage and damage where known.
- Flash Flood
- Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
- Excessive Heat and Heat in Arizona, August 1 to 6, 202125 deaths · 31 events
- Flash Flooding and Flooding in Utah, August 1 to 2, 20211 death · 1 injured · $12 million · 1 in hail · 21 events
- Drought in South Dakota, August 1 to 31, 2021$19 million · 24 events
- Wildfire and Astronomical Low Tide in California, August 1 to 31, 20211 death · 2 events
- Wildfire in Oregon, August 1 to 31, 20211 death · 1 event
- Drought in Minnesota, August 1 to 31, 2021$5.7 million · 8 events
- Drought in Iowa, August 1 to 31, 2021$2.1 million · 9 events
- Wildfire in Washington, August 1 to 30, 2021$1.1 million · 1 event
- Flash Flooding and Heavy Rain in Nevada, August 1 to 2, 2021$800,000 · 3 events
- Hail and Damaging Winds in Texas, August 1, 2021$374,000 · 1.75 in hail · 11 events
- Flash Flooding and Heavy Rain in Colorado, August 1, 202176 events
- Drought in Nebraska, August 1 to 31, 2021$286,000 · 2 events
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: 976604, 976601.