An area of showers and thunderstorms formed over Nez Perce County during the morning hours of May 18th. 17 inches of rain from these storms.
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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.
An area of showers and thunderstorms formed over Nez Perce County during the morning hours of May 18th. Lewiston ASOS reported 0.99 inches of rain while the COOP Observer at Nez Perce reported 1.17 inches of rain from these storms. This rain produced a number of secondary road washouts and minor main road damage through out the county. In the Lewiston area urban flooding affected parking lots and poor drainage properties including a number of apartments in Lewiston.
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 18, 1:28 AM PST, 32 minutes earlier.
Area Forecast Discussion National Weather Service Spokane WA 228 AM PDT Fri May 18 2018 .SYNOPSIS... The arrival of a cold front on tonight and Friday will produce breezy north and northeast winds and cooler temperatures closer to average. More showers but fewer thunderstorms can be expected for Saturday...but Sunday looks like a dry break period. A warming trend will develop next week but with more showers and thunderstorms possible. && .DISCUSSION... Today through Saturday: An area of low pressure remains embedded between split flow over the Western US. This pattern will continue to promote cooler and showery conditions as various smaller scale disturbances rotate in and around it through Saturday. The atmosphere is showing less instability than when this pattern first moved into position and as such the forecast is trending more towards more cloudiness and slow moving showers and less in the way of thunderstorms. In addition a cold front dropping down along the edges of the low will allow the surface pressure gradient to favor a wind shift to north and northeast today. /Pelatti Sunday and Monday: Sunday will be the driest and warmest day of the weekend as we transition between the upper low exiting to the northeast and the new trough moving onshore from the Pacific. This weak ridge of rising heights will help keep showers mainly limited to the mountains surrounding the basin. We'll remain under moist southwesterly flow on the eastern side of the trough which will bring good WAA and high temps 4-8 degrees warmer than Saturday (highs in the mid 70s). By Monday the trough will have split into two areas of circulation, one that dips well to our south and pinches off over the desert southeast, and one that stays further north. There is considerable disagreement on the exact track of this northern branch which will affect just how showery we are to start the week. Generally the main trough feature stays to our south, actually shifting flow out of the east/southeast and pulling moisture around said low and all the way up into our region. This will keep Monday showery, with thunderstorm potential. The best chance will be southeast WA/ID Panhandle and the northern mountains/Cascades where upslope showers are most favorable. Tuesday-Thursday: A messy pattern continues. Earlier it seemed a stronger ridge would move in for a break in the showers, but models have been trending much weaker and more transient with this feature in the latest runs. It now looks that the offshore ridge tries to move in Tuesday but the desert southwest low dominates the flow, moving north toward our region. This keeps moist flow around with an unstable airmass. This will mean daily shower and thunderstorm chances for most of the region. Given the moist air and and weak steering flow these storms will have potential to drop localized heavy rain. Temperatures will also continue to climb into at least Wednesday, topping out about 10 degrees above normal for late May, in the 80s. Looking out into the far extended period there is high uncertainty given polar opposite solutions from synoptic models which disagree on whether we'll see a break in the showery pattern by late week. /bw .Hydrology...With the cooling trend expected this weekend mountain snow melt will slow down...however the warming trend beginning early next week will allow another acceleration. So for the foreseeable future little relief is expected for the river flooding issues plaguing the region. The following rivers are currently under river Flood Warnings... Moyie River at Eastport AFFECTING Boundary County Lake Pend Oreille AFFECTING Bonner County Kettle River near Ferry above Curlew AFFECTING Ferry County Methow River near Pateros AFFECTING Okanogan County Okanogan River near Tonasket AFFECTING Okanogan County Pend Oreille River below Albeni Falls AFFECTING Bonner and Pend Oreille Counties Similkameen River near Nighthawk AFFECTING Okanogan County The Flash Flood Watch will continue indefinitely for the Lost River community in the Methow Valley for possible levee failure. An Areal Flood Warning continues over Okanogan County for the lake shore of Lake Osoyoos...and the possibility of renewed rainfall and snow melt related flooding on the Salmon Creek and Chewuck River. An Areal Flood warning remains in effect for a sliver of Ferry and Stevens county along the Kettle River from the Canadian border to Lake Roosevelt, in addition to the riverine Flood Warning for the Kettle River near Ferry. && .AVIATION... 06Z TAFS: Lightning around the Moses Lake Area this evening should dissipate by 08Z tonight. Low pressure will sit over southern WA will result in light rain across much of the region through at least early Friday afternoon. Low cigs with IFR/MVFR conditions will be likely around the Spokane Area, Pullman to Lewiston and over the basin, including into KMWH and KEAT. Cigs may lift through Friday afternoon, but expect mountain obscurations through the day. Expect gusty northeast at KCOE up to 25 kts Friday morning and afternoon. /SVH && .PRELIMINARY POINT TEMPS/POPS... Spokane 62 49 67 49 75 54 / 60 30 40 10 10 10 Coeur d'Alene 61 47 67 47 75 51 / 40 20 30 10 10 10 Pullman 59 48 67 48 73 51 / 90 40 50 10 10 20 Lewiston 64 53 73 53 78 56 / 80 40 50 10 10 20 Colville 65 48 70 48 77 50 / 40 20 20 10 10 10 Sandpoint 64 45 65 44 74 47 / 30 20 40 10 10 10 Kellogg 59 43 64 45 73 48 / 40 40 30 10 10 10 Moses Lake 66 52 73 50 79 54 / 80 40 20 10 10 10 Wenatchee 64 53 71 53 77 55 / 90 40 40 10 20 10 Omak 65 52 71 52 77 53 / 90 40 20 20 10 10 && .OTX WATCHES/WARNINGS/ADVISORIES... ID...None. WA...None. &&
Hazardous Weather Outlook National Weather Service Spokane WA 820 AM PDT Thu May 17 2018 IDZ001>004-026-027-WAZ036>038-042-043-181530- Northern Panhandle-Coeur d'Alene Area-Idaho Palouse- Central Panhandle Mountains-Lewiston Area- Lewis and Southern Nez Perce Counties-Spokane Area- Northeast Mountains-Okanogan Highlands- East Slopes Northern Cascades-Okanogan Valley- 820 AM PDT Thu May 17 2018 This Hazardous Weather Outlook is for portions of North Idaho... North Central Idaho...North Central Washington and Northeast Washington. .DAY ONE...TODAY AND TONIGHT Area rivers remain high, with some flooding in the Idaho Panhandle and extreme northern Washington. Although the probability for widespread hazardous weather is low, scattered thunderstorms are possible today. Some of these storms may slow moving and contain brief heavy rain. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY Many area rivers will see rises and become very high through the week with additional snow melt, with some flooding in the Idaho Panhandle and extreme Northern Washington. WAZ031>035-041-044-181530- Northeast Blue Mountains-Lower Garfield and Asotin Counties- Washington Palouse-Moses Lake Area-Upper Columbia Basin- Wenatchee Area-Waterville Plateau- 820 AM PDT Thu May 17 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 Area rivers remain high, with major flooding on some rivers in the area. Although the probability for widespread hazardous weather is low, scattered thunderstorms are possible today. Some of these storms may slow moving and contain brief heavy rain heightening the possibility of flash flooding on recent burn scars. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY Many area rivers will remain in flood through the next week as mountain snow melt continues.
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
Five main and 4 secondary roads in Latah County were washed out or otherwise damaged by heavy rains.
Heavy rain in and around Lewiston created numerous urban flooding problems during the morning of July 18th. A retention pond overflowed and caused a hillside washout with another hillside also suffering erosion damage. A number of roads and parking lots were flooded in the city and a block of apartments in low laying poor drainage areas suffered first floor and yard flooding.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2018Every state in 2018This day in weather historyWarnings in Idaho, 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: 758589, 758611.