To illustrate, take a look at the sea level pressure forecast for tomorrow (Wednesday) at 10 AM. An amazing large and intense low pressure area over the Pacific. In fact, it appears to cover virtually the entire NE Pacific!
Rain returns tomorrow afternoon, but with this large low over the NE Pacific, most of the flow will go south of us into southern Oregon and northern CA. Here is the forecast precipitation for the 72 hr ending Saturday at 4 AM. Huge amounts over northern CA.
Update Wed AM
Easterly flow in the foothills can produce large temperature variations. While many locations cooled into the 30s last night, those areas experiencing easterly (downslope) flow are in the upper 40s and even lower 50s. Here are temps at 6 AM this morning...look carefully and you will see this big contrasts over the eastern part of the terrain (the map extends from Seattle to North Bend)::