The map below from NWS shows a FLOOD WATCH for all of western Oregon and southwest Washington (dark green color), starting this evening and lasting into Wednesday morning.
A warm front will bring developing rain or showers today. The main event begins this evening with hours of steady rain.
Hours of mostly steady rain Tuesday into Wednesday morning will be heaviest Tuesday overnight as a low pressure center nears the coast and a cold front arrives into Wednesday morning. 60-hour rain totals during the event could bring 4” of rain to the coast, 2.50” to the I-5 corridor and 6” or more to the mountains. Snow levels will rise above 6,000 feet. Areas of high water will develop Tuesday. 6-8” of water in the Coast Range will likely cause some rivers to reach flood stage Tuesday overnight into Wednesday morning.
Rain will be heavy enough Monday night to cause high water spots Tuesday morning on area roadways.
A FLOOD WATCH continues today for our region. Rain totals since last evening are generally around
an inch here in the valley, which matches forecast projections. Steady rain continue to fall today, tonight and much of Monday with an additional 1-2” of rain, pushing storm totals to 2.50 - 3.25” over Portland and Salem. The front that arrived last night will orientate parallel to the upper wind flow and hold stationary over Portland today. A secondary low center will arrive Monday afternoon or evening and push the frontal boundary through Portland and off to the east. Rain will break up Monday night and dry weather will take hold Tuesday. Winds will calm a bit on this Sunday and be variable 5-25 mph, but southwest gusts Monday will pick back up 20-35 mph. Snow level today near 6,500 feet. Heavy rain will continue at pass level the next 24 hours.
Weather models show breaks in the rain Sunday afternoon north of Vancouver and possible breaks in the rain Sunday overnight and Monday morning for much of our region, including Portland and Salem as the rain area pushes north of Portland. The trailing low center arriving Monday, will bring a return of steady rain to the I-5 corridor. The 3-day rain episode will end Monday overnight or early Tuesday morning.