PORTLAND, Ore. (KOIN) — Mother Nature is flipping the switch this weekend as Saturday brings fall-like conditions to the Portland area for the first official day of autumn.

An atmospheric river is starting to take shape over the Pacific Ocean this weekend. The brunt of the storm will be felt next week, but cooler and rainier weather returns Saturday.

Clouds will begin to increase Saturday as spotty showers increase the coast just before sunrise. Not everyone will see heavy rain Saturday, but cooler temperatures will be widespread along with the cloud coverage.

KOIN 6 Meteorologist Josh Cozart shares the Willamette Valley’s rain timeline Saturday

Saturday’s rainfall totals will be minimal for many. Rain will struggle to make its way over the Cascades for the start of the weekend, but coastal communities could see as much as a quarter of an inch by the end of the day Saturday.

Western Oregon and Washington’s forecast rain totals for Saturday, September 23, 2023

Even more rain is possible Sunday. Rain showers will start to increase throughout the day Sunday as temperatures struggle to warm into the low 70s. Mid to upper 60s are likely through the day and will continue into next week.

Sunday’s rainfall totals for western Oregon and Washington on September 24, 2023

The brunt of the atmospheric river is likely Sunday night and continue to the start of next week. The total rain accumulation expected for the area starting Saturday through the middle of next week will be the greatest amount of rain seen in the Pacific Northwest this season.

Forecast rain totals from Saturday to Wednesday evening as an atmospheric river returns to the Pacific Northwest

The KOIN 6 News Weather Team has high confidence in the development of the summer season ending rain.

KOIN 6 News Weather Team has high confidence in the development of an atmospheric river over western Oregon and Washington next week

This weekend and next week’s rain could push parts of the area above average rainfall totals for September’s monthly rainfall. Portland should typically see 1.52″ of rain in the month of September. The Rose City has already managed to pick up 0.03″ of rain, which puts the city below normal by nearly an inch.