Montana, 2020Flood in Montana, May 20, 2020
May 20, 2020 · NWS MSO · 1 event in 1 county or zone
Widespread rainfall of 1 to 2 inches, combined with high elevation snow melt, brought small stream flooding and river rises.
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- Deaths
- 0
- Injuries
- 0
- Property damage
- None recorded
- Crop damage
- None recorded
- Events
- 1
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.
Widespread rainfall of 1 to 2 inches, combined with high elevation snow melt, brought small stream flooding and river rises.
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 May 20, 1:58 AM MST, 5 hours 2 minutes earlier.
Area forecast discussion, May 20, 1:58 AM MST, 5 hours 2 minutes before
Area Forecast Discussion
National Weather Service Missoula MT
258 AM MDT Wed May 20 2020
.DISCUSSION...Lingering embedded thunderstorms remain within the
spinning low pressure centered around the Northern Rockies this
morning. Moderate to heavy rainfall that occurred overnight across
west central Montana has moved into northwest Montana and north
central Idaho. These areas will continue to see the best focus of
rainfall throughout the day. A brief drying period may occur
across southwest Montana into portions of west central Montana (in
and around the Missoula/Bitterroot valleys) for a period of time
this afternoon, but will eventually fill back in with more
rainfall by this evening.
With widespread moderate to heavy rainfall expected through
Thursday, our main concern continues to be rapid rises on small
streams and creeks and mainstem rivers rising above flood stage.
Particular emphasis is given to small streams/creeks across north
central Idaho, as this is where the heaviest rainfall will exist
today. Loose soil, sloughing of land, rock fall over highways, etc
should also be anticipated due to persistent heavy rainfall.
Mainstem rivers across the entire region will continue
to rise as well, albeit somewhat slower though not any less
significant. Flood Watches and Warning(s) remain in effect across
west central Montana and north central Idaho, however additional
Watches/Warnings may need to be issued as this system evolves
further.
Rain will remain somewhat consistent in the forecast through
Friday, with periodic breaks finally happening thereafter.
While rainfall will become less widespread, it will still remain
a fixture going into the weekend.
&&
.AVIATION...Moderate to heavy rainfall will plague KMSO, KGPI, and
KGIC throughout the day today, with breaks in precipitation
occurring for KBTM and KSMN through this afternoon. With the low
pressure center expected to revolve around the Northern Rockies
over the next 24-48 hours, persistent rainfall should be expected.
Low ceilings will be commonplace, with periodically lowered
visibility in areas of particularly heavy rain. Mountain
obscurations will exist henceforth under this unsettled and wet
pattern.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through late tonight Bitterroot/Sapphire Mountains...
Missoula/Bitterroot Valleys.
ID...Flood Watch through late tonight Lower Hells Canyon/Salmon River
Region...Northern Clearwater Mountains...
Orofino/Grangeville Region...Southern Clearwater Mountains.
&&Flood, Ravalli
- When
- May 20, 7:00 AM MST to 5:00 PM MST
- Where
- Ravalli County, 3.07 mi NW of Victor to 2.41 mi N of Florence
- Cause
- Heavy Rain / Snow Melt
- Reported by
- Broadcast Media
- Coordinates
- 46.453, -114.194
Swollen small streams brought flooding to fields and low-lying areas in the Bitterroot Valley. A few homes were surrounded by water and reported water in basements. Local and county roads, along with a small section of Eastside Highway north of Stevensville, experienced water flowing across roadways. A Forest Service campground south of Darby was also closed because of the stream flooding. In addition, the Bitterroot River rose enough to flood ranch fields around Lolo.
- Flood
- Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
After NWS Directive 10-1605, the rules offices file Storm Data by.
- Hail in Texas, May 20, 2020$100 million · 3 in hail · 9 events
- Strong Wind in Minnesota, May 20, 20201 death · 1 event
- Tornado and Hail in Montana, May 20, 2020$737,000 · EF0 · 49 events
- Flash Flooding and Flood in South Carolina, May 20 to 21, 2020$211,000 · 3 events
- Tornado and Hail in South Carolina, May 20, 2020EF1 · 10 events
- Flooding in Ohio, May 20 to 23, 2020$34,000 · 8 events
- Flash Flooding and Flooding in West Virginia, May 20 to 22, 2020$35,000 · 7 events
- Damaging Winds in Florida, May 20 to 24, 2020$25,000 · 65 kt wind · 9 events
- Hail and Damaging Winds in Montana, May 20, 20202.5 in hail · 21 events
- Damaging Wind in Colorado, May 20, 2020$15,000 · 70 kt wind · 1 event
- Tornadoes and Hail in Colorado, May 20, 2020EF0 · 8 events
- Hail in Wyoming, May 20, 20202 in hail · 7 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: 884060.