Thunderstorm Wind — Spokane, Washington

2014-08-02 · near Hite, Spokane, Washington

Event narrative

Numerous trees were downed or snapped across Northern Spokane County including the communities of Deer Park, Chattaroy, Colbert, Mead, Nine Miles Falls, and Spokane north of Interstate 90 due to a west to east tracking outflow boundary. A second cell developed along the boundary producing quarter size hail over Five Mile Prairie and sent an outflow boundary north to south across the South Hill and Spokane Valley roughly thirty minutes after the initial gust front went through. A NWS employee stated winds associated with this boundary were less than 25 mph but witnessed a tree fall down. Due to its isolated nature, it is assumed that this tree was damaged from a storm two weeks earlier. Significant damage was observed from northwestern Spokane to Chattaroy to the Pend Oreille County border. The Riverside Mobile Home Park was hit hard for a second time in as many weeks and forced to evacuate. Numerous trees fell on homes. One home on North Echo Road suffered major structural damage. The nearby Eloika Lake Resort lost eight trees in the storm. The trees damaged a home, RVs, and vehicle. The resort which lost 48 trees in a storm ten days earlier was forced to shut down for the remainder of the summer.

Wider weather episode

A strong upper-level ridge during the end of July and beginning August helped fuel a moist and unstable air mass over the region. The ridge broke down on the 1st of August and was overrun by two weak midlevel impulses on August 2nd. As the second impulse passed over Central Washington during the late afternoon, strong to severe storms developed over the Waterville Plateau producing a combination of heavy rain and moderate size hail. Meanwhile, dewpoint depressions over Eastern Washington had grown between 40 and 50 degrees Fahrenheit. The rain and hail cooled outflow winds from storms over the Waterville Plateau spread east and gained momentum while tracking along the Highway 2 corridor across the Upper Columbia Basin. Additional storms fired along the gust front and continued to reinforce the cold pool and resultant winds. Gusty winds and blowing dust which originated over the Waterville Plateau traveled across Banks Lake and through much of Lincoln County but generally remained below severe speeds. It wasn't until the outflow boundary moved into Eastern Lincoln County and Lake Roosevelt near Seven Bays Marina when wind speeds ranged between 60 and 70 miles per hour. The winds led to numerous downed trees, waves four to six feet on Lake Roosevelt, widespread boat damage, power outages, and structural damage. The winds also fanned new wildfire starts from lightning. As the afternoon progressed, a combination of forcing from the shortwave and gust front continued to fuel additional storms over Northeastern Washington. Outflow winds from these storms generally moved north to south. As the north to south boundaries interacted with the westerly boundaries, some locations were spared experiencing wind gusts between 35 and 45 mph. In this absence, winds of 50 to 70 mph were observed coupled with widespread tree damage. A few storms briefly produced quarter size hail between Davenport and Northwest Spokane.

View location on OpenStreetMap → (47.6489, -117.8339)

Source: NOAA Storm Events Database, event_id 534572. Narrative written by the NWS forecast office that issued the report.