These weekend Seattle will be warm and dry with temperatures 10F and more above normal. Some of you might see 90F.
At the same time, San Diego, a place with the average rainfall of Yakima, will be preparing for an unusual onslaught of moisture from Tropical Cyclone Norbert. The latest infrared satellite picture (9:30 PM Friday PDT) shows the storm off southern Baja California and moisture streaming northward in advance of it.
This moisture will reach the San Diego area tomorrow, greatly increasing the chance of strong thunderstorms, particularly over the mountains east of the city. Take a look at the cumulative precipitation over the next 78 hr (through 11 PM Monday). The Northwest is practically the driest place in the nation. But you can see the impacts of Norbert over the the Southwest, with 2-3 inches reaching the San Diego area. Not the weather that surfer folks like!
Around here you can expect a further warm up in western Oregon and Washington. Here are the max temps on Friday. 90s in the Willamette Valley. Lower 80s in southern Puget sound, and 70s over NW Washington. Add 5-10F tomorrow.
There is no better tool for warming periods than UW Probcast and here is the forecast from that system for Seattle. 86F tomorrow and a modest cool-down to 81F on Sunday. Temps will be warmer on the eastside of Puget Sound
This warm-up is being aided by easterly offshore flow that isolates us from the cool waters of the Pacific and which produces compressional warming as the air sinks on the eastern slopes of the Cascades. You can see the easterly flow in this plot of winds above Sea-Tac Airport (temps are shown in red). The x-axis is time (increasing to the left) and the y axis is height in pressure (850 hPa is around 5000 ft). A thin veneer of northerlies near the surface with easterlies aloft.
A series of weak upper troughs will approach late Sunday and Monday resulting in a marine push and cool down. But don't worry, the ridge will be back later in the week.
Folks in San Diego will be flying up here for dry, warm conditions. You've got to feel sorry for them.
If anyone is interested, I will be doing a weather segment on SandBox radio...the Seattle version of Prairie Home Companion. Will take place at ACT Theater, downtown Seattle, this Monday evening (Sept 8). To spice it up, Steve Scher will be on the program as well! No dueling will be allowed. For more information: check here.