Timeline: Atmospheric river impacts on Oregon, Washington this weekend

PORTLAND, Ore. (KOIN) -- An unseasonably strong and late atmospheric river is expected to impact much of the Pacific Northwest on the first weekend of June.

Atmospheric rivers are a common occurrence during the winter months for the west coast, but this weekend's wet weather event is abnormally late. Over half of Portland's monthly rainfall for June is expected to accumulate within the first few days of the month. Portland normally sees 1.63" of rain in June, but forecast models are predicting over an inch of rain from Saturday to Monday.

Rain timeline for Portland area

Increasing clouds early Saturday morning will continue to keep temperatures cooler and skies gray for the first day of June. One or two of those clouds could bring a scattered rain shower or two to the region.

Portland's Rose Festival City Fair isn't expected to see anything more than slightly cooler and cloudier conditions on Saturday. The same raindrop or two could potentially take Portland into the Starlight Parade time frame. The chance for rain remains minimal on Saturday evening. A stray, light, and fast-moving shower or two is possible by the end of the event, but will have very little impact on parade-goers.

Persistent and heavy rain isn't expected to move into western Oregon and southwest Washington until Sunday morning. Sunday will likely be one of the rainier days of the atmospheric river event.

Rain showers are expected to last well into Monday evening. Nearly an inch and a quarter of rain is expected with this late-season rain event. June is typically Portland's fourth driest month of the year, but has been as wet as 4.27" in 2010 when Portland saw the most rainfall ever recorded in the month of June.

Some outdoor activities will be impacted by the return of heavy and persistent rain during the second half of the weekend. This wet weather trend quickly comes to an end by the middle of next week. Warmer, more summer-like temperatures and conditions are expected around Portland. Some of the warmest temperatures of the year so far are expected by the end of next week in Portland.