Plaincast

Synopsis

Persistent onshore flow will bring near-average temperatures with varying degrees of morning clouds and afternoon sunshine for much of the next week. A series of weak fronts will bring notable chances for light rain and drizzle to portions of the Washington and north Oregon coasts Tuesday and next weekend, while Friday is likely to be the warmest day.

Discussion

Now through Sunday. The large-scale pattern remains fairly steady through the next week with the region wedged between upper-level troughing over the Gulf of Alaska and upper-level ridging over the Rockies and Central Plains. In general, the weather locally will be typical for the mid-summer: morning clouds followed by increasing afternoon sunshine, seasonable temperatures, and largely dry conditions, but with some variations as the strengths of these two dominant features change relative to one another.

Today, upper ridging wins out as heights aloft rise marginally, yielding clouds clearing all the way to the coast by the early afternoon with seasonably warm high temperatures in the 60s on the coast and mid 80s within the Willamette Valley. On Tuesday, an upper shortwave passing to the north will tilt the scales in favor of upper troughing, sending a weak front toward the coast resulting in cooler temperatures across the region and chances for light rain or drizzle along the coast and Coast Range, increasing from 40% at Florence to 60% at Newport, 75% at Tillamook, 95% at Astoria, and nearly 100% on the Long Beach Peninsula. Chances for accumulating rainfall are lower along the I-5 corridor, ranging from 20% at Salem to 30% at Portland, 60% at Woodland, and 75% at Kelso/Longview.

Through the latter half of the workweek, the upper-level ridge will strengthen and retrograde westward into the Great Basin, increasing heights aloft locally and again tipping the balance toward warm and dry weather. As such, temperatures will trend upward each afternoon, peaking on Friday in the upper 60s to around 70 degrees on the coast and in the mid to upper 80s within inland valleys. Despite this trend, onshore flow will continue, limiting the risk for hazardous heat. Minor HeatRisk is favored for the entire region on Friday, with 20-40% chances for Moderate HeatRisk in urban and suburban areas from Salem north to Vancouver, WA. By next weekend, there continues to be higher uncertainty in the evolution of the upper-level pattern, but many ensemble members depict more pronounced troughing returning to the Pacific Northwest, favoring cooler temperatures and further chances for rainfall. The details of timing and potential rainfall amounts remain fuzzy at this lead time, but those near the coast or within coastal terrain will be the most likely beneficiaries of any rainfall, with chances increasing to the north. -36