Idaho, 2020Debris Flow in Idaho, July 3 to 10, 2020
July 3 to 10, 2020 · NWS MSO · 1 event in 1 county or zone
Heavy rainfall at the end of June likely contributed to a rock slide that closed both lanes of US Route 95 south of Riggins, ID.
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- Deaths
- 0
- Injuries
- 0
- Property damage
- $180,000
- 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.
Heavy rainfall at the end of June likely contributed to a rock slide that closed both lanes of US Route 95 south of Riggins, ID.
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 3, 1:59 AM PST, 8 hours 1 minute earlier.
Area forecast discussion, Jul 3, 1:59 AM PST, 8 hours 1 minute before
Area Forecast Discussion
National Weather Service Missoula MT
359 AM MDT Fri Jul 3 2020
.DISCUSSION...Clearing overnight has helped with the formation of
some valley fog in NW Montana. Otherwise, mostly sunny conditions
today will lead to temperatures reaching well into the 80s and
perhaps just a touch above normal for today. As broad troughing
across Western Canada and the United States deepens along the
Pacific Coast, the ensuing southwesterly flow will gradually bring
increasing chances for showers and thunderstorms to southwest
Montana this afternoon and evening. Some models show a secondary
disturbance sliding across NW Montana which may keep some
convection going overnight. But any storms that do form will be
weak and isolated.
A similar pattern is expected on Independence Day (Saturday),
though the temperatures should be a bit cooler due to increased
cloud cover. All the models seem to agree that a rather vigorous
disturbance will propagate across the Northern Rockies during the
afternoon hours, kicking off fairly widespread showers and
thunderstorms over much of the area. The most consistent area of
focus for storms appears to be south and east of a line from
Riggins, Idaho NE through Missoula and then towards Swan Lake. So
it seems entirely possible that parts of SW and West Central
Montana could experience some of nature's fireworks along with the
various shows expected within the area. While a few storms could
grow strong, possessing brief heavy rain, lightning and small
hail; the threat for anything stronger still seems very limited
right now.
Drier conditions are expected on Sunday with temperatures still
hovering near normal. Overall, you can pretty much put that
forecast on repeat for much of next week as the general weather
pattern (Western Canada/Western USA troughing) continues.
Inevitably there will be a more favorable day for showers and
thunderstorms and the current models support sometime around
midweek right now. However, specifics regarding timing or aerial
coverage are still too challenging to forecast.
&&
.AVIATION...Some patchy fog has formed this morning within the
valleys of NW Montana. Some limitations to visibility will be
possible at KGPI, but any impacts will be brief. Otherwise rather
pleasant flying conditions will be in place throughout the region
this morning. Some breeziness is possible this afternoon and a few
showers and/or thunderstorms are expected across SW Montana.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
Debris Flow, Idaho
- When
- July 3, 10:00 AM PST to July 10, 12:00 AM PST
- Where
- Idaho County, 1.39 mi NE of Pollock to 1.38 mi NE of Pollock
- Cause
- Heavy Rain
- Property damage
- $180,000
- Reported by
- Department of Highways
- Coordinates
- 45.332, -116.347
Between 28-30 June 1.67 of rain was measured at the Riggins COOP (45.42/ -116.31). Around 10 AM on the 3rd a rockslide was reported near mile marker 188 on US Route 95 in Idaho. This slide closed both lanes of the highway. A bypass was built and opened on the 9th, however instability in the slope continued to hinder repair (which continued through much of the summer).
- Debris Flow
- A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.
After NWS Directive 10-1605, the rules offices file Storm Data by.
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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: 899798.