Thunderstorms and heavy rain have hit the eastern slopes of the Cascades and portions of eastern Washington and Oregon, with a little spill-over over the upper slopes of western WA.
Take a look at the radar imagery tonight around 7:15 PM from the Spokane and Portland radars (see below). Lots of echos east of the crest with very heavy rainfall over the eastern slopes near Wenatchee and Leavenworth.
The showers were so intense near Wenatchee that there was localized flooding and mudslides. Here are a few pictures courtesy of the Wenatchee World newspaper:
According to the Washington State DO, US 97 A, milepost 220 to 222, is closed over night due to heavy rain fall, mud and debris over the roadway.
Why the thunderstorms? The air east of the Cascades has been relatively unstable and a weak upper level trough (see below) has been moving through the east side, providing enough lift to release the instability (producing thunderstorms). The lightning detection network indicates hundreds of lightning strikes. This is not a good thing since they have the potential to initiate wildfires. In fact, one such lightning-produced fire was reported near Yakima.
More thunderstorms are expected east of the Cascade crest the next few days...so if you want rain you know where to go!