Spring time mountain snow melt and a period of moderate rain during the second week of May created saturated soil conditions over Ferry County. A debris flow deposited rocks onto Highway 395 near Orient, which is a major highway route through the region.
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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.
Spring time mountain snow melt and a period of moderate rain during the second week of May created saturated soil conditions over Ferry County. A debris flow deposited rocks onto Highway 395 near Orient, which is a major highway route through the region.
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 May 10, 4:47 PM PST, 2 hours 43 minutes earlier.
Area Forecast Discussion National Weather Service Spokane WA 547 PM PDT Thu May 10 2018 .SYNOPSIS... An upper level low will drop through the Inland Northwest through tonight, with scattered showers, isolated evening thunderstorms and cooler, breezy weather. High pressure arrives for the weekend with warm and dry weather that continues into the middle of next week. Flooding concerns will continue on many of the area rivers. && .DISCUSSION... Tonight through Friday...The main active weather period will occur over the next 24 hours as an upper level low pressure descends through the forecast area from north to south...with instability showers and isolated thunderstorms into this evening across most of the forecast area...a weak wrap-around band of showers hooking from the north to south over the deep basin and Cascades overnight tonight...and more showers with a smaller but still present chance of thunderstorms Friday afternoon mainly over far eastern Washington and the Idaho Panhandle. Satellite clearly indicates the circulation over eastern Washington this evening. Daytime surface heating coupled with cooling aloft in the approaching center of the upper low has effectively destabilized the air mass...and vorticity energy in the low center is efficiently exploiting available moisture and instability into a field of showers and a few thunderstorms over most of the forecast area...with only the Wenatchee/Leavenworth region benefiting from downslope. Much of this convective activity will die with the sunset as surface temperatures cool and promote better stability. However the offending upper low will remain a player overnight as the center passes to near the Idaho/Washington/Oregon triple point border and a field of moisture currently visible on the back side of it over southern BC drops southward through the western zones overnight tonight. Most high resolution models handle this wrap around surge as an area of minor showers or even light rain passing north to south through the Columbia Basin overnight...with a few hundredths to a worse case 1 tenth of an inch of rain in the deep basin and Cascades east slopes before moving out of the area by dawn. It is possible this axis may wind up displaced eastward a bit so it is not safe to totally eliminate any chance of showers anywhere in the forecast area tonight even after the daytime convection tapers off. On Friday the upper low will be well south of the region over southern Idaho...but more wrap around moisture will hook in from the east and bring a continuing chance of showers to the southeastern zones nearest to the closed low. Also...more instability...although not as strong as this afternoon...will be generated with afternoon heating over the Idaho Panhandle and extreme eastern Washington for another small chance of afternoon and early evening hit-and-miss showers and isolated garden variety thunderstorms. Some residual showers are also possible over the high terrain of the Cascades but will be highly terrain based and short lived if they occur at all. Friday night through Thursday...Active weather ends during this period. All the latest medium range models are in remarkably good agreement through at least next Tuesday in building a ridge aloft over the forecast area flopping over the closed low which by then will be sulking over the Great Basin for a few days before minoring out. This model agreement promotes high confidence of dry conditions with a warming trend through the weekend and at least into into early next week. Even though differences in details become apparent between models after Tuesday...where agreement exists suggests a deep closed low near the California coast with the forecast area a bit too far north to be significantly impacted by any moisture surges up the east flank of this feature. Thus there is no compelling reason at this time to expect any precipitation chances through the end of the extended period. It will get warm though. High temperatures in the high 70s and lower 80s will be common by Sunday in the basin and valleys across the region...peaking on Monday and then stabilizing for the rest of the forecast period. Mountain snow melt will probably accelerate during this period and this bodes ill for any foreseeable significant flooding relief for the numerous rivers draining the mountainous regions. /Fugazzi && .Hydrology... Rainfall no longer looks like a significant player for additional flooding concerns around the region. High elevation snow melt over the next week will be the primary driver for increasing river flows...as well as dam releases on some rivers to alleviate anticipated reservoir storage concerns. The following mainstem rivers around the area remain under River Flood Warnings... Methow River St Joe River Kettle River Moyie River Okanogan River Pend Oreille River Similkameen River In addition Areal Flood Warnings remain in effect for... North Fork of Salmon Creek in Okanogan County. Salmon Creek in Okanogan County. Lake Osoyoos shoreline in Okanogan County. Chewuch River in Okanogan County. /MJF && .AVIATION... 00Z TAFS: Cold pool aloft and afternoon heating will result in widely scattered showers with isolated t-storms through 02z. Thereafter...scattered showers are expected to accompany smaller waves pinwheeling around the large scale low over the region. Winds will be chaotic around convective showers and storms then look to decrease around 10kts this evening except at KEAT which will maintain stronger NW fLow. Showers will concentrate over SE WA this evening and slowly depart to the SE Fri morning. One more disturbance tracking NE to SW through N ID and far eastern reaches of WA will bring one last round of afternoon convection with KCOE...KSFF...KGEG...KPUW...KLWS carrying a brief window to be impacting btwn 22-01Z. /sb && .PRELIMINARY POINT TEMPS/POPS... Spokane 45 66 47 74 50 78 / 50 20 10 0 0 0 Coeur d'Alene 44 65 43 74 47 78 / 50 30 10 0 0 0 Pullman 43 59 42 71 46 74 / 40 30 30 0 0 0 Lewiston 48 62 45 76 50 79 / 20 30 20 0 0 0 Colville 45 70 44 80 47 84 / 70 20 10 0 0 0 Sandpoint 43 63 41 73 44 77 / 50 20 10 0 0 0 Kellogg 41 60 39 69 43 73 / 60 60 20 0 0 0 Moses Lake 50 73 48 81 50 84 / 60 20 0 0 0 0 Wenatchee 50 71 51 80 55 83 / 60 30 10 0 0 0 Omak 48 72 48 81 52 84 / 60 20 0 0 0 0 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. &&
Hazardous Weather Outlook National Weather Service Spokane WA 500 AM PDT Thu May 10 2018 IDZ001>004-026-027-WAZ031-036>038-042-043-111200- Northern Panhandle-Coeur d'Alene Area-Idaho Palouse- Central Panhandle Mountains-Lewiston Area- Lewis and Southern Nez Perce Counties-Northeast Blue Mountains- Spokane Area-Northeast Mountains-Okanogan Highlands- East Slopes Northern Cascades-Okanogan Valley- 500 AM PDT Thu May 10 2018 This Hazardous Weather Outlook is for portions of North Idaho... North Central Idaho...North Central Washington...Northeast Washington and Southeast Washington. .DAY ONE...TODAY AND TONIGHT Isolated thunderstorms are possible this afternoon and early evening, with the potential for brief heavy downpours and small hail. Heavy downpours may lead to localized ponding of water. Although the probability for widespread hazardous weather is low. Many area rivers will remain very high with some flooding in the Idaho Panhandle and extreme northern Washington. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY Many area rivers will remain very high with some flooding in the Idaho Panhandle and extreme northern Washington. WAZ032>035-041-044-111200- Lower Garfield and Asotin Counties-Washington Palouse- Moses Lake Area-Upper Columbia Basin-Wenatchee Area- Waterville Plateau- 500 AM PDT Thu May 10 2018 This Hazardous Weather Outlook is for portions of Central Washington...East Central Washington...North Central Washington and Southeast Washington. .DAY ONE...TODAY AND TONIGHT Isolated thunderstorms are possible this afternoon and evening with brief downpours and small hail. Although the probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY No hazardous weather is expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SPOKANE WA
645 PM PDT THU MAY 10 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0641 PM DEBRIS FLOW 4 SSE ORIENT 48.80N 118.16W
05/10/2018 FERRY WA DEPT OF HIGHWAYS
ROCK SLIDE ON SOUTH BOUND US395 NEAR MP 254
NEAR HODGSON-LAKIN RD. EXACT TIME OF SLIDE
UNKNOWN. DELAYS TO HIGHWAY WERE EXPECTED AS
ROCK WAS REMOVED.
&&The national radar mosaic for the moment the first event began.
1 debris flow. Local standard time, as filed.
A small debris flow deposited rock onto the southbound lane of Highway 395 near Orient. Traffic was delayed as the rock was removed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Washington in 2018Every state in 2018This day in weather historyWarnings in Washington, May 2018
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: 758815.