Well, Autumn sure is in a hurry! From the National Weather Service:
The first organized storm system of the season for NW OR and SW WA arrives tonight. An early fall storm system will bring a drastic change in weather overnight into Wednesday. The main weather impact will be widespread moderate to heavy rain that will spread inland from the coast tonight.
Rainfall totals by the end of the day Wednesday are expected to be mainly between half an inch to one and a half inches. This may result in some ponding of water in low lying areas.
Motorists are urged to use caution on the roadways. Given the long period of dry weather that has preceded this front, residual oil and grease on the road surfaces can become slick.