Warm temperatures in early May prompted accelerated snow melt in the mountains of British Columbia. Run off from this snow melt caused multiple areal flooding issues in Okanogan County during the second and third week of May. Lake Osoyoos began rising rapidly during the second week of May. Flooding occurred on properties along the lake shore during the second and third weeks of May as the water level peaked and stabilized. The water level began to recede on May 19th and continued to fall through the end of the month.
Salmon Creek near Conconully also rose out of it's banks due to snow melt in the higher elevations of the north Cascades. This river caused minor flooding problems in the town of Conconully and lead to a road closure along the southern stretch of river.
The Chewuch River draining the north Cascades through Winthrop also rose out of it's banks causing minor flooding of roads and a few homes in the Winthrop area.
All of these flooding issues along with the major flood along the Okanogan River prompted the county to be included in a State of Emergency Declaration issued by the Washington State Governor.

Flood in OKANOGAN, WASHINGTON
From 09-MAY-18 12:00:00 to 19-MAY-18 03:00:00 (PST-8)
Location: OKANOGAN
Flood cause: Heavy Rain / Snow Melt
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Emergency Manager

On May 8th Conconully Lake reached the spillway level on the Conconully Dam due to heavy Spring runoff from the upper reaches of the Salmon River. The increased flow caused flooding along the river below the dam and resulted in the flooding and subsequent closure of Salmon Creek Road between Spring Coulee Road and Danker Cutoff Road.

Flood in OKANOGAN, WASHINGTON
From 06-MAY-18 18:00:00 to 20-MAY-18 07:00:00 (PST-8)
Location: CONCONULLY
Flood cause: Heavy Rain / Snow Melt
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The City of Conconully reported that the North Fork of Salmon Creek had a rapid rise on May 6th, causing water to flow over the Broadway Street Bridge. Over a span of the next  two weeks, the North Fork rose and fell daily with the diurnal snow melt cycle, causing the water to occasionally flow over the bridge.

Flood in OKANOGAN, WASHINGTON
From 09-MAY-18 00:00:00 to 18-MAY-18 00:00:00 (PST-8)
Location: WINTHROP
Flood cause: Heavy Rain / Snow Melt
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Newspaper

Spring time snow melt caused the Chewuch River near Winthrop to rise and cause minor flooding during the second and third weeks of May. Roads and fields along the river were inundated and a few homes suffered yard inundation and first floor minor flooding.

Flood in OKANOGAN, WASHINGTON
From 09-MAY-18 13:00:00 to 23-MAY-18 14:00:00 (PST-8)
Location: OROVILLE SCOTT ARPT
Flood cause: Heavy Rain / Snow Melt
Property damage: 200.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The USGS Lake Level Gage at Osoyoos Lake near Oroville recorded a  steady rise in the lake level beginning on May 5th. There is no official Flood Stage for this lake. The Lake level peaked at 916.5 feet on May 12th, and remained slightly above 916 feet through May 20th before steadily falling through the end of the month.

Flood in OKANOGAN, WASHINGTON
From 09-MAY-18 13:00:00 to 23-MAY-18 14:00:00 (PST-8)
Location: OROVILLE SCOTT ARPT
Flood cause: Heavy Rain / Snow Melt
Property damage: 2.00M
Crop damage: 0.00K
Reported by: Emergency Manager

The rise on Osoyoos Lake, which has no official Flood Stage, began to flood properties and seep into homes around the lake shore beginning on May 9th.  By the morning of the 10th  flood waters had submerged Deep Bay Park and were flooding the basements and threatening the first floors of homes along Blackler Road and the boat launch along Veranda Drive.  As the lake crested and the level stabilized between May 11th and May 19th extensive flooding of low lands along the lake was noted with Veterans Memorial Park completely inundated. Numerous lake shore homes suffered first floor flooding during this crest period.