Hot and unstable conditions with mid level monsoonal moisture created conditions ripe for gusty thunderstorms over north central Idaho during the afternoons of August 29th and 30th. During the afternoon of August 29th thunderstorms developed over extreme northeast Oregon and tracked into Nez Perce and Lewis Counties in Idaho.
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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 OTX wrote it up.
Hot and unstable conditions with mid level monsoonal moisture created conditions ripe for gusty thunderstorms over north central Idaho during the afternoons of August 29th and 30th.
During the afternoon of August 29th thunderstorms developed over extreme northeast Oregon and tracked into Nez Perce and Lewis Counties in Idaho. These storms produced wind gusts which downed trees and damaged structures in the Kamiah area. A nearby remote weather station recorded a peak wind gust of 94 mph as these storms passed through.
The next day on August 30th another round of afternoon high based thunderstorms produced a microburst which created extensive damage to power lines along a stretch of Highway 64 on the Camas Prairie.
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 Spokane, WA wrote its last area forecast discussion before the first event at Aug 29, 1:50 PM PST, 59 minutes earlier.
Area Forecast Discussion National Weather Service Spokane WA 250 PM PDT Tue Aug 29 2017 .SYNOPSIS... Haze and smoke will persist over the Inland Northwest through Wednesday. The arrival of a cold front Wednesday night should bring cleaner air into the Inland Northwest by Thursday. Locally breezy conditions will accompany the cold front late in the day Wednesday and into Thursday. A return of much above average temperatures is expected for the Labor Day weekend. && .DISCUSSION... Tonight into Wednesday: A broad Pacific trough will gradually move inland late tonight into Wednesday. The incoming trough will draw mid and high level moisture out of Ern Oregon and the Great Basin into the Idaho Panhandle and far eastern Washington tonight and Wednesday morning. Most of the moisture will be above 10 thousand feet, but there will be sufficient instability aloft to produce widely scattered showers. Don't expect much rain with these small cells as they move from southwest to northeast tonight and tomorrow morning. Very dry air below the high cloud bases will promote a good deal of evaporation as precip falls to the ground. Evaporative processes will contribute to the potential for gusty outflow from showers with localized gusts of 30 to 40 mph. The amount of lightning this evening into Wednesday is a very tough call. Forecast soundings from the GFS and NAM show little more than a sliver of most unstable CAPE between 500-300mb. The incoming trough and deep layer warm/moist advection will provide some lift, but there is not strong Q-Vector convergence...meaning no strong kicker for thunderstorm development. At this time, it looks like widely scattered lightning will be possible, but not enough to warrant a Red Flag Warning for "abundant lightning". Wednesday evening through Thursday: Temperatures will be trending down Wed into Thu as onshore flow increases allowing a gradual influx of air with more of a marine influence to spread through the Cascade gaps. Look for winds to increase in the afternoon and evening around Wenatchee, Vantage, Entiat, and Chelan with gusts of 25 to 30 mph. For the rest of the region, sustained west or southwest winds of 10 to 15 mph are expected Wed afternoon and again on Thu. /GKoch Thursday night through Tuesday: In the wake of Thursday's cold front passage high pressure returns and the ridge aloft builds up again. Winds are on the decrease Thursday night and the low level thermal features then show the heat trof redeveloping off the California coast and creeping slowly northward over the weekend. The upper level ridge axis getting positioned off the coast coupled with the low level thermally induced low pressure area creeping up the California coast allows for a change in the flow and as such the flow has potential to be lighter with hints of flow from the north and northeast. Disturbances dropping down the ridge to the west are likely to increase this pressure gradient at times favoring the flow from the north and northeast. This change is likely to end the trend of importing smoke from Oregon fires and may allow for some British Columbia wildfire smoke to return at times (if those fires take a turn for the worse and burn with the intensity they did back in early August) otherwise no significant weather systems are expected to trek through with this change in weather pattern so pops for precipitation remain low to zero. A repeat pattern of a marine surge ahead of a negatively tilted cold front passage Monday night/Tuesday looks possible to briefly interrupt this pattern by pushing the ridge axis back east and over Eastern Washington. /Pelatti && .AVIATION... 18Z TAFS: Widely scattered showers will move across the Idaho Panhandle and the eastern third of Washington today and tonight. Pilots should be aware of the potential for gusty outflow with these showers. Gusts of 30 to 40 mph may be possible with these little cells around Pullman and Lewiston. Even if thunder and lightning is not present, rain falling into an air mass this hot and dry has the potential to produce dry microburst type winds. Elsewhere haze and smoke will potentially drop visibility as low as 3 miles. Most of our smoke is coming from SW Oregon which is somewhat diffuse compared to the thicker smoke from nearby fires west of Ellensburg. Westerly drainage winds late tonight into Wednesday could potentially influence the visibility at Wenatchee and Chelan. && .PRELIMINARY POINT TEMPS/POPS... Spokane 66 90 59 83 58 86 / 10 20 0 0 0 0 Coeur d'Alene 61 91 56 83 54 86 / 20 20 0 0 0 0 Pullman 62 90 53 82 53 86 / 20 20 0 0 0 0 Lewiston 68 94 62 88 60 92 / 20 30 10 0 0 0 Colville 55 91 54 87 51 88 / 10 10 0 0 0 0 Sandpoint 52 90 51 82 48 84 / 20 20 0 0 0 0 Kellogg 59 89 55 81 52 84 / 20 20 0 0 0 0 Moses Lake 59 93 58 88 55 92 / 10 10 0 0 0 0 Wenatchee 65 90 64 87 63 91 / 0 0 0 0 0 0 Omak 61 94 59 89 58 93 / 0 0 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. &&
Hazardous Weather Outlook National Weather Service Spokane WA 608 AM PDT Tue Aug 29 2017 IDZ001>004-WAZ033>038-041>044-301315- Northern Panhandle-Coeur d'Alene Area-Idaho Palouse- Central Panhandle Mountains-Washington Palouse-Moses Lake Area- Upper Columbia Basin-Spokane Area-Northeast Mountains- Okanogan Highlands-Wenatchee Area-East Slopes Northern Cascades- Okanogan Valley-Waterville Plateau- 608 AM PDT Tue Aug 29 2017 This Hazardous Weather Outlook is for portions of North Idaho... Central Washington...East Central Washington...North Central Washington...Northeast Washington and Southeast Washington. .DAY ONE...TODAY AND TONIGHT No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY No hazardous weather is expected at this time. IDZ026-027-WAZ031-032-301315- Lewiston Area-Lewis and Southern Nez Perce Counties- Northeast Blue Mountains-Lower Garfield and Asotin Counties- 608 AM PDT Tue Aug 29 2017 This Hazardous Weather Outlook is for portions of North Central Idaho and Southeast Washington. .DAY ONE...TODAY AND TONIGHT No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY Isolated dry thunderstorms will be possible each Tuesday and Wednesday afternoons. Wednesday carries a slightly higher risk. With any storms that do form...gusty outflow winds near 45 mph and new fire starts will be possible.
The Pendleton radar (KPDT), 156 km away, was scanning. The volume nearest the first event began at 22:46 UTC.
4 thunderstorm wind. Local standard time, as filed.
The Corral Creek remote weather station recorded a wind gust of 94 mph. Radar indicated a thunderstorm just to the south of the station at the time of the gust.
Several trees uprooted and split, with large branches broken off due to thunderstorm winds.
A series of photographs from the Lewis County Emergency Manager indicated numerous trees down in Kamiah, with damage to outbuildings, a barn and at least one car in and around the town.
The Lewis County Emergency Manager reported 13 power poles knocked down and multiple transformers damaged along Highway 64 between Lyons Rd. and Marker Rd. Power was cut off to the area for 18 hours while repairs were made. Radar indicated a thunderstorm nearby which likely produced a strong microburst into the damage area.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2017Every state in 2017This day in weather historyWarnings in Idaho, August 2017
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: 720130, 717531, 720136, 720134.