70 degrees is no longer normal in Seattle.
Today marks the first day since June 13 where the average high temperature is below 70—with 69 degrees the normal high for Sept. 20. Right on cue, after a week with readings in the 70s and 80s, the mercury dropped back to more seasonable levels today, with Sea-Tac topping out at 67 degrees.
Similar temperatures are in store tomorrow, with highs struggling to reach the upper 60s after another round of chilly morning fog. Late in the afternoon, we’ll warm up as sunshine takes hold, but until then, expect gray skies and temperatures only in the 50s.
Saturday will be even cooler yet, with temperatures falling into the mid- to lower-60s. Amazingly, if we don’t reach 65, we’ll end a 90-day stretch of temperatures at or above 65 degrees—Seattle’s second-longest, according to the National Weather Service. Heck, even sultry Chicago’s seen a colder day more recently.
With the cooler weather will also come a change in the large-scale weather pattern, as a ridge of high pressure overhead gives way to an upper-level low. The low, currently over the eastern Pacific, will move toward the Washington coast on Saturday, dragging up unstable air as it does. By Saturday night, isolated thunderstorms will be possible over Central Washington, the Cascades and outlying areas of Seattle—especially southeast of the city.
These storms are expected to generate plenty of lightning and wind—but little to no moisture—potentially making the nightmarish wildfire situation around Wenatchee and Ellensburg even worse. In response to this, the National Weather Service has issued a Fire Weather Watch for much of the state, from east of I-5 all the way to the Tri-Cities.
The upper-level low drifts into Oregon on Sunday, ending the thunderstorm threat. Skies will remain cloudy most of the day in Seattle, however, with high temperatures only in the upper 60s.
The new normal around here.