An upper level low pressure system over western Oregon ejected a negatively tilted shortwave trough of lower pressure over the region during the evening hours of September 5th.  Precipitable water values were twice the normal value for early September.  A line of strong thunderstorms tracked across east-central Washington bringing strong winds and heavy rain.  The hardest hit areas were across the Waterville Plateau, the Wenatchee area and east slopes of the northern Cascades.  Strong winds did result in some fallen trees, but the greatest impact was due to the heavy rainfall.  Training thunderstorms and intense rainfall resulted in flash flooding across multiple drainages.  Recent burn scars from 2012 and 2013 wildfires also helped to create a damaging flash flood event.

Thunderstorm Wind in DOUGLAS, WASHINGTON
From 05-SEP-13 20:25:00 to 05-SEP-13 20:40:00 (PST-8)
Location: BRIDGEPORT
Magnitude: 41.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Newspaper

A tree was knocked down across a roadway.  Time was estimated based off of radar.  Damage costs were also estimated.

Thunderstorm Wind in DOUGLAS, WASHINGTON
From 05-SEP-13 20:30:00 to 05-SEP-13 20:40:00 (PST-8)
Location: ORONDO
Magnitude: 50.00 EG
Crop damage: 0.00K
Reported by: Newspaper

Tree fell onto mobile home that briefly trapped the occupants.  Bedroom door was damaged and occupants had to crawl through an opening to the hallway to escape.  Minor injuries were sustained to an adult female and a child.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 19:00:00 to 05-SEP-13 22:00:00 (PST-8)
Location: MALAGA
Flood cause: Heavy Rain / Burn Area
Property damage: 700.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A flash flood down the Colockum Creek drainage washed out Tarpiscan Road at the Colockum Creek bridge.  Colockum Road, Kingsbury Road, and Agnew Road were closed due to the damage.  Multiple homes were damaged along the Colockum Creek Drainage as well by rocks, trees and other debris that traveled with the flood wave.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 20:00:00 to 05-SEP-13 22:45:00 (PST-8)
Location: WEST WENATCHEE
Flood cause: Heavy Rain
Property damage: 43.43K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash flooding from Number 2 Canyon blocked a portion of Number 2 Canyon Road above milepost 3.  Flood waters reached as far as western Wenatchee.  Flood waters also damaged homes and property to private residences in the Canyon.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 20:30:00 to 05-SEP-13 22:45:00 (PST-8)
Location: CHUMSTICK
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Heavy rain caused mud and debris to block a portion of Eagle Creek Road.  Damage costs were estimated.

Flash Flood in DOUGLAS, WASHINGTON
From 05-SEP-13 20:20:00 to 05-SEP-13 22:30:00 (PST-8)
Location: MC CARTENEY
Flood cause: Heavy Rain
Property damage: 20.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A flash flood deposited mud and rocks approximately two feet deep over Jameson Lake Road at Sulphur Springs Road.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 20:30:00 to 05-SEP-13 22:45:00 (PST-8)
Location: LEAVENWORTH
Flood cause: Heavy Rain
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Flash flooding and debris on Fourth of July Creek above Icicle Creek closed off National Park Road 76.  Many campers were stranded above where the flash flood occurred until the road was cleared of debris.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 22:15:00 to 06-SEP-13 01:00:00 (PST-8)
Location: STEHEKIN
Flood cause: Heavy Rain
Property damage: 330.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Flash flooding and debris traveled down Imus Creek near Stehekin and covered approximately 350 linear feet of Stehekin Valley Road.  Mud and debris covered the road up to eight feet deep in spots.  Several vehicles and bicycles in a parking area were damaged and/or pushed into Stehekin Lake.  An office and residential building were surrounded by mud and debris, but only received minimal interior flood damage.  Damage costs were estimated.

Debris Flow in CHELAN, WASHINGTON
From 05-SEP-13 22:30:00 to 05-SEP-13 23:00:00 (PST-8)
Location: STEHEKIN
Flood cause: Heavy Rain
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Newspaper

A debris flow blocked the road to Harts Pass just below Deadhorse Point.  The slide continued down onto Lost River Road near the River Bend Campground.  Mud and debris accumulated to about five feet in depth across the road.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 23:00:00 to 06-SEP-13 02:00:00 (PST-8)
Location: STEHEKIN
Flood cause: Heavy Rain
Property damage: 110.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Highway 20 was closed across Chelan County due to flash flooding and debris flows.  Damage costs were estimated.

Flash Flood in CHELAN, WASHINGTON
From 05-SEP-13 21:00:00 to 05-SEP-13 22:45:00 (PST-8)
Location: MONITOR
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Park/Forest Service

Several flash floods and debris flows across a three mile stretch of Mission Creek Road from milepost 4 to milepost 7.  Damage costs were estimated.

Flash Flood in GRANT, WASHINGTON
From 05-SEP-13 22:30:00 to 06-SEP-13 01:00:00 (PST-8)
Location: HANSON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

X-NE Road was covered by water and mud for approximately 100 to 150 yards and appeared to be deep in sections.  It was likely that the road was impassable during the flash flood, but there were no reports of impacts during the event.  Timing of the flash flood was estimated by radar.

Flash Flood in OKANOGAN, WASHINGTON
From 06-SEP-13 13:45:00 to 06-SEP-13 16:30:00 (PST-8)
Location: TONASKET
Flood cause: Heavy Rain
Property damage: 23.00K
Crop damage: 0.00K
Reported by: Department of Highways

A flash flood washed out approximately 200 yards of a portion of the eastbound lane of Highway 20 at milepost 266.  One lane was kept open for traffic.  Damage cost were estimated.