Flood — Okanogan, Washington

2017-04-04 to 2017-04-30 · near Mazama Arpt, Okanogan, Washington

Event narrative

Areal Flooding, mudslides and debris flows in rough terrain plagued Okanogan County during the month of April as a result of saturated soil conditions brought on by periodic heavy rain and spring snow melt.

At least 24 roads through out the county were closed or damaged by washouts and debris flows during the month.

Most notably, State Route 20, a main east to west route between Twisp and Okanogan was cut by a washout on April 7th near mile post 221 and then suffered a second washout on April 15th near mile post 211. Both washouts cut deep chasms through the road bed and closed a 10 mile section of the highway through the rest of the month and into May. Five residences between these washouts were isolated while the road was repaired.

A second major route through the county, State Route 153, was cut by a debris flow on April 7th causing a temporary closure of a three mile stretch near Pateros.

Salmon Creek near Conconully flooded and damaged summer homes and properties along it's banks.

Wider weather episode

In addition to a wet March, periodic heavy rains continued during the month of April. In Ferry County, the COOP station at Republic recorded 2.93 inches of rain for the month, which is 1.42 inches above average. In Okanogan County the Omak ASOS station recorded 2.66 inches of rain, which is 1.62 inches above average. At Mazama the COOP observer recorded 2.45 inches of precipitation, which is 1.42 inches above average.

All of this rain on top of spring time snow melt promoted saturated soil conditions which resulted in numerous debris flows and areal and small stream flooding issues through out Ferry and Okanogan Counties during the month of April.

Ferry County had been experiencing these issues through the end of March but more rain in April aggravated the situation resulting in major debris flows and flooding which cut key roads through the county. The Sanpoil River also flooded to levels which a media statement issued by the Ferry County Sheriff's Office and the Colville Tribal Police described as the worst flooding in decades.

Okanogan County largely escaped problems during the month of March but April brought the axis of periodic heavy rain storms and accelerated low elevation snow melt to this county. Saturated soil conditions, often over extensive recent burn scars, resulted in numerous debris flows and small stream floods which disrupted travel for much of the month and isolated a few back country residents for long periods of time. Highway 20, one of the major roads through the region remained closed over Loup Loup Pass while major repair work continued into the month of May.

View location on OpenStreetMap → (48.9881, -120.8167)

Source: NOAA Storm Events Database, event_id 693231. Narrative written by the NWS forecast office that issued the report.