A line of strong thunderstorms moved across northeast Oregon/southeast Washington late Thursday afternoon/early evening and were starkly evident in the NWS radar at Pendleton (see below for 6:49 PM). The heaviest precipitation is shown by the red colors.
Strong winds gusting above 50 mph accompanied the thunderstorms and to illustrate this, here are the Doppler winds from the Pendleton radar (shows the wind velocities towards or away from the radar) at 7:24 PM for the lowest (.5 degree) scan angle. Some winds exceeded 30 knots at this level (undoubtedly stronger winds below).
Here are the wind observations at Walla Walla Airport (sustained winds shown by the line, gusts by marker) on Thursday. Gusts got up to roughly 55 mph! There was a number
Pacific Power reported 2841 customers lost power in Weston, Milton-Freewater, and Walla Walla due to broken power poles and power lines down from the wind.
Getting back to the shelf cloud, here is another example from the storm provided by Ryan Mclaughlin. These features are often called arcus or roll clouds. They represent the forward edge of the gust front of the thunderstorm. Cool downdraft air moves outward from the thunderstorm, causing warmer air in front of it to rise and form a linear cloud feature (see the schematic below). They do look very ominous and are associated with very large vertical wind shear...so NEVER dry to fly through one of these if you are a pilot.
We are in for a wet period during the next day as a low pressure system moves across northern Oregon. Here is the 24-h rainfall ending 5 PM on Sunday....a soaker in the Cascades and western Oregon. This represents a relatively rare pattern where eastern Washington gets plenty of precipitation. Want to be dry? Head to British Columbia or the NW tip of the Olympic Peninsula.