A ridge of high pressure over the region for the last few weeks was nudged east by a potent upper-level trough coming off the Eastern Pacific.  The trough took on a strong negative tilt and passed through during peak heating.  An east to west line of strong thunderstorms developed over Northern Oregon and tracked northward through Eastern Washington and Northern Idaho during the late afternoon and early evening.  Additional storms continued to develop along the gust front which picked up momentum as it passed into the region into an inverted V environment.  The outflow winds picked up dust through Northern Oregon and Southern Washington resulting in a damaging dust storm or haboob.  Visibility along Interstate 90 was reduced below a quarter of a mile and numerous locations clocked winds between 50 and 60 mph resulting in isolated downed trees and power outages.  Proactive measures were taken at the Grant County Fair hours before the storm hit with nearly 8000 people evacuated and the fair cancelled to ensure the safety of the staff and attendees.  Reduced visibility from the dust led to multiple accidents in the Columbia Basin.

Dust Storm in UPPER COLUMBIA BASIN, WASHINGTON
From 12-AUG-14 16:30:00 to 12-AUG-14 16:40:00 (PST-8)
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Near zero visibility due to a haboob or dust storm contributed to a six vehicle accident along Interstate 90 twenty-two miles west of Ritzville.  Five people were injured in the accident.  A second accident was contributed to the dust involving two cars on Highway 395 twenty-six miles south of Ritzville.

Thunderstorm Wind in WHITMAN, WASHINGTON
From 12-AUG-14 15:19:00 to 12-AUG-14 16:50:00 (PST-8)
Location: RIPARIA
Magnitude: 35.00 MS
Property damage: 0.20K
Crop damage: 0.00K
Reported by: Mesonet

A line of winds sustained 30 to 45 mph with gusts ranging between 50 and 65 mph blew through Whitman County ahead of a line of thunderstorms.  Visibility across western sections of the county lowered below a quarter mile due to blowing dust.  Numerous tree limbs were down across the town of Palouse ranging between four and six inches in diameter.

Dust Storm in WASHINGTON PALOUSE, WASHINGTON
From 12-AUG-14 15:19:00 to 12-AUG-14 16:50:00 (PST-8)
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A wall of dust from thunderstorm winds resulted in near zero visibility across areas of Whitman County.  Two semi trucks crashed on State Route 26 in the town of Dusty.

Debris Flow in OKANOGAN, WASHINGTON
From 12-AUG-14 21:20:00 to 12-AUG-14 21:40:00 (PST-8)
Location: CARLTON
Flood cause: Heavy Rain / Burn Area
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Route 153 was closed at Cow Creek due to a mudslide approximately one foot deep covering eighty feet of the roadway.  The slide crossed the road and went into the Twisp River.  Mud and rocks washed on to Route 20 near Loup Loup Pass from Frazer Creek.  A second hand report stated that a motorcyclist accident occurred at the location of the flow due to the motorcyclists attempting to drive through the mud.  It is unclear if the motorcyclist saw the mud or not.  It is unclear if the motorcyclist was injured.  French Creek at Burma Road flooded sending water and some debris onto private property and up to four homes.  At least two homes got some mud and water into home.

Thunderstorm Wind in STEVENS, WASHINGTON
From 12-AUG-14 17:20:00 to 12-AUG-14 18:00:00 (PST-8)
Location: WELLPINIT
Magnitude: 51.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Wind gusts of 50 to 60 mph crossed into southern Stevens County resulting in isolated downed trees and power outages.  The storm weakened while crossing into central sections of the county.

Debris Flow in CHELAN, WASHINGTON
From 12-AUG-14 22:55:00 to 12-AUG-14 23:15:00 (PST-8)
Location: STARR
Flood cause: Heavy Rain / Burn Area
Property damage: 0.10K
Crop damage: 0.00K
Reported by: Other Federal Agency

Debris flow down the Chiwaukum Creek caused a two foot flood wave near Highway 2 and mouth of the creek.

Thunderstorm Wind in SPOKANE, WASHINGTON
From 12-AUG-14 16:40:00 to 12-AUG-14 18:30:00 (PST-8)
Location: SPRING VLY
Magnitude: 41.00 MG
Property damage: 350.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Numerous power lines were knocked down between Spokane and Chattaroy due to winds sustained between 25 and 35 mph with gusts 45 to 55 mph.  A brush fire destroyed three outbuildings and damaged a house near Mt Spokane Park Drive and Peone Road.

Thunderstorm Wind in LINCOLN, WASHINGTON
From 12-AUG-14 16:22:00 to 12-AUG-14 17:46:00 (PST-8)
Location: DOWNS
Magnitude: 52.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Public

Sustained winds of 30 to 45 mph with gusts to 60 mph knocked down trees in Harrington and produced a wall of dust across Lincoln County.  Visibility was reduced below a mile along sections of Highway 2 as the storm moved through.  A sensor at the Sevens Bay Marina clocked a wind gust of 59 mph.

Thunderstorm Wind in ADAMS, WASHINGTON
From 12-AUG-14 15:37:00 to 12-AUG-14 16:20:00 (PST-8)
Location: WASHTUCNA ARPT
Magnitude: 52.00 MG
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Public

A large tree was blown down at a golf course in Ritzville.

Strong Wind in MOSES LAKE AREA, WASHINGTON
From 12-AUG-14 16:30:00 to 12-AUG-14 17:30:00 (PST-8)
Magnitude: 37.00 MS
Property damage: 0.20K
Crop damage: 0.00K
Reported by: Mesonet

Outflow winds sustained 30 to 45 mph with gusts to 56 mph passed through Grant County.  Visibility at the Moses Lake Airport dropped near one mile due to blowing dust from the wind.  No damage was reported around the county but the anticipated winds and dust lead to the closure and evacuation of 8000 people at the Grant County Fair hours before the winds arrived.

Thunderstorm Wind in OKANOGAN, WASHINGTON
From 12-AUG-14 17:50:00 to 12-AUG-14 18:45:00 (PST-8)
Location: COULEE DAM
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: NWS Employee

IMET stationed in Nespelem Fire Camp received winds between 50 and 60 mph along with blowing dust.  The winds knocked trees down, tossed boxes, tents, tarps, and signs around fire camp.  Several porta potties were knocked down as well.  The storm weakened as it reached Brewster, Okanogan, and Omak.  These areas received wind gusts near 35 mph which blew down small branches causing some isolated power outages in the community of Twisp.

Thunderstorm Wind in FERRY, WASHINGTON
From 12-AUG-14 17:50:00 to 12-AUG-14 18:30:00 (PST-8)
Location: KELLER
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Thunderstorm winds of 50 to 60 mph carried a wall of dust into southern Ferry County.  Isolated power line and tree damage was noted across far southern sections of the county.  Power lines were downed on the Colville Reservation along Highway 21 between Keller and mile post nine.