SEATTLE, WASHINGTON — A cooler weather pattern is pushing into the Pacific Northwest as a deep offshore trough settles just west of Washington and Oregon by Monday, bringing widespread showers, falling temperatures, and even a non-zero chance of isolated lowland snow across parts of the region.
Forecast model data highlights a pronounced 500mb trough positioned just offshore, signaling a shift away from recent milder conditions toward a colder, more unsettled pattern. This upper-level setup is expected to dominate through early next week, supporting below-normal temperatures and periodic precipitation across Western Washington, Western Oregon, and into parts of Southwest British Columbia.
Deep Offshore Trough Brings Cooler Air Into Washington and Oregon
Ensemble guidance shows a well-defined dip in upper-level heights along the Pacific Northwest coastline. The deep trough offshore enhances onshore flow, allowing cooler marine air and instability to spread inland. The placement of this system just west of Vancouver Island, extending south toward Oregon, is key to keeping temperatures suppressed.
Surface temperature guidance shows readings in the 30s to low 40s across much of Western Washington, including Seattle, Tacoma, and Olympia, with colder pockets over higher terrain. Overnight lows dipping into the low-to-mid 30s raise the potential for mixed precipitation in some lower-elevation areas if heavier showers develop…