Moist, southerly flow ahead of an area of low pressure trickling northward along the Oregon Coast created a moist, unstable environment over Central Washington.  Shortwaves ejecting from the shortwave trough supplied the necessary lift to initiate numerous strong thunderstorms across the East Slopes of the Cascades and portions of the Western Columbia Basin.  These storms developed during the evening and overnight hours of August 9th and persisted well into the morning hours of August 10th.  Storms dissipated around midday then afternoon heating and a second shortwave triggered another round of strong storms during the afternoon and evening hours of the 10th.  The main threat with these storms was high rain intensity and flash flooding, however one line of storms also delivered damaging winds.

Thunderstorm Wind in CHELAN, WASHINGTON
From 10-AUG-13 21:58:00 to 10-AUG-13 22:45:00 (PST-8)
Location: STAYMAN
Magnitude: 52.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Utility Company

Chelan County PUD reported numerous downed trees and power poles along the southern end of Lake Chelan.  Some apple trees in nearby orchards were also damaged.

Debris Flow in CHELAN, WASHINGTON
From 10-AUG-13 23:40:00 to 11-AUG-13 00:55:00 (PST-8)
Location: MANSON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Highway 971 was closed between mile markers nine and eleven due to a mudslide blocking the highway.

Debris Flow in CHELAN, WASHINGTON
From 10-AUG-13 23:20:00 to 10-AUG-13 23:45:00 (PST-8)
Location: ENTIAT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Highway 97 alternate was blocked temporarily at milepost 212 due to a small mudslide.

Debris Flow in CHELAN, WASHINGTON
From 11-AUG-13 17:25:00 to 11-AUG-13 17:50:00 (PST-8)
Location: MALAGA
Flood cause: Heavy Rain / Burn Area
Property damage: 700.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Heavy rain from a slow moving thunderstorm fell over the 2013 Colockum Tarps burn scar leading to flash flooding, a massive debris flow, and significant property damage.  One debris flow occurred down Robinson Canyon and across Colockum Road cutting through a home and barn along the way.  The home had water and debris flowing through it and out the front windows.  Residents escaped through the front windows and climbed a tree until water receded.  A large boulder went through the corner of the barn.  Asphalt was removed from Colockum Road between Colockum Creek and Kingsbury Road.  Kingsbury bridge over Colockum Creek also sustained minor damage.  Flash flooding was also observed down the Colockum Creek drainage to the intersection of Tapiscan and Colockum Roads.  Water washed out Colockum Road at mile post 12 making the road impassible.  A mobile home on Tarpiscan Road at the bottom of the drainage was washed off its foundation.  The residents in the mobile home were able to make it to higher ground before it washed away.  Flash flooding was also reported by the public down the Dry Gulch drainage located south of the Colockum Creek drainage.  Flood waters and debris led to the washout of the Dry Gulch Bridge on Colockum Road making the road impassible.

Thunderstorm Wind in DOUGLAS, WASHINGTON
From 10-AUG-13 21:45:00 to 10-AUG-13 22:30:00 (PST-8)
Location: COLUMBIA RIVER
Magnitude: 52.00 EG
Property damage: 80.00K
Crop damage: 100.00K
Reported by: NWS Storm Survey

Numerous trees and power lines were downed from thunderstorm winds across southern Douglas County.  Two large trees, estimated to be two feet in diameter, were downed at Desert Canyons Lodge.  In Orondo, three large trees, estimated to be two feet in diameter and 120 feet tall, were knocked into high voltage power lines starting a small fire.  At least 50 apple trees across multiple orchards were also damaged from the high winds.  In Waterville, two downed trees landed on houses along Poplar Street and numerous large limbs were on the ground throughout town.

Thunderstorm Wind in GRANT, WASHINGTON
From 10-AUG-13 21:20:00 to 10-AUG-13 21:45:00 (PST-8)
Location: QUINCY
Magnitude: 52.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

High winds uprooted a 40 foot tree onto a car in southeastern sections of Quincy.  Power and phone outages were reported across southwestern sections of town.  Six inches of standing water was on sections of Highway 28 in town.

Flash Flood in CHELAN, WASHINGTON
From 10-AUG-13 20:40:00 to 10-AUG-13 21:40:00 (PST-8)
Location: MALAGA
Flood cause: Heavy Rain / Burn Area
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A few basements and outbuildings were flooded from heavy rain.  Colockum Creek flowed out of its banks and across Colockum Road just upstream of the intersection with Kingsbury Road.  There was no damage to the road but a fence on the adjacent property did sustain some damage.

Debris Flow in DOUGLAS, WASHINGTON
From 10-AUG-13 22:50:00 to 10-AUG-13 23:10:00 (PST-8)
Location: WATERVILLE
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Highway 2 at Pine Canyon was closed due to mud and debris covering the roadway for a period of time.  The road was covered in six to eight inches of debris.  The water dug three to four foot trenches within the drainage.  The Douglas RAWS reported six tenths of rainfall in an one hour period.

Thunderstorm Wind in OKANOGAN, WASHINGTON
From 10-AUG-13 23:43:00 to 11-AUG-13 00:05:00 (PST-8)
Location: WINTHROP ARPT
Magnitude: 76.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: RAWS

A collapsing thunderstorm and microburst was thought to be responsible for localized damaging winds near the city of Winthrop during the overnight hours of August 10th.  The NCSB RAWS station located four miles south southeast of Winthrop clocked a gust of 87 mph.  Several trees were damaged or blown down at the Bear Creek Golf Course but no other damage was reported with this storm.

Debris Flow in CHELAN, WASHINGTON
From 10-AUG-13 11:50:00 to 10-AUG-13 12:10:00 (PST-8)
Location: WEST WENATCHEE
Flood cause: Heavy Rain / Burn Area
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rainfall led to a debris flow across Number Two Canyon Road roughly from mile post three to the end of the pavement around 0000 PST.  The slide left half to one foot of mud and debris, including rocks, over the roadway rendering the road impassible.  The Number One Canyon Near Wenatchee Rain Gauge (NOOW1) received 0.29 of rainfall over a span of 29 minutes.  Runoff incised ditches up to four feet in diameter exposing utilities.