Cooling Ocean Breezes Bring Rain to Portland Area This Weekend

PORTLAND, Ore. — Cooling ocean breezes poured inward Thursday evening, rapidly dropping temperatures around 70 degrees at 9 p.m.

After a heat wave that saw Portland top 99 degrees for three consecutive days, the region is set for a change. While the area remains warm, with temperatures around 90 degrees south of the metro, forecasts indicate a cooling trend of 4-8 degrees for Friday.

Beginning Friday and continuing into early Saturday, a rare summertime Atmospheric River will impact the region. This weather pattern is created by an upper-level low offshore and a deep southwesterly flow.

According to meteorological models, this system, positioned at around 30,000 feet, will bring significant moisture to western Washington. Although the system is expected to move quickly, with moisture dissipating over northeast Oregon within 18 hours, rain amounts will vary across the area.

In the western Willamette Valley and the west metro areas, forecasts suggest less than half an inch of rain due to being “rain-shadowed” by the Coast Range. However, the west slopes of the Cascades and Coast Range are expected to receive a soaking, with rainfall amounts ranging from 2 to 4 inches.

Weather models indicate that areas like Forest Grove might only see 0.25 inches, while Gresham could receive up to 1.25 inches as precipitation moves from west to east across the metro area. This weather pattern is described as a steady and moderate overnight rainfall rather than thunderstorms.

After the rainfall, the outlook for Saturday and Sunday is mainly dry, attributed to the upper-level low remaining offshore. A weak system moving northward across eastern Oregon Sunday could trigger some strong thunderstorms, although it is still uncertain.

The projected rainfall is expected to pause fire season activities during what is typically the most critical period for wildfires in the region, allowing outdoor events like barbecues, weddings, and reunions to proceed without weather interruptions.