It was a warm, cloudy day here in the Northwest with large contrasts of rain (see figure below of the observed 24-h precipitation ending 7 PM Thursday): over 3 inches in the Olympics, but only light rain over the lowlands, and a few sprinkles across the basin of eastern WA. Why so little over the Cascades but lots over the southern slopes of the Olympics? The key reason is that the flow aloft was southerly (from the south) and you can't get good upslope on the Cascades from the direction. But you can get good upslope over the south-facing slopes of the Olympics.
But the real precipitation story is to our south, over southern Oregon and northern CA, where some locations got over four inches (pink color) and over two inches was commonplace. But this is just the beginning.
Flooding is inevitable.
Take a look at the latest UW WRF model precipitation forecast for the next 72 h: huge amounts, including over 10 inches in "favored" upslope locations. The Olympics and north Cascades are also wet.