Sunday, September 20, 2009
Super-Ridge and Late September Heat Wave
Last week I was in California...dropping my son off at college and visiting Yosemite Park. It was hot down there...even reaching 90F in the Yosemite Valley, but that is nothing compared to what is going to happen during the next few days--both down there and up here in the NW.
Take a look at the temperatures of the past two weeks (see figure above). In general, the high temps have been at or above normal...and the minimum temperature much above normal. But real heat is about to turn on.
A huge, high-amplitude upper ridge is developing over the west coast (see forecast for Tuesday morning). This is really amazing...with unusually high pressure developing aloft and at low levels. Such a major ridge is associated with warm temps aloft and with offshore flow and added warming at low levels. Look at the computer forecast for Tuesday (see figure). Very, very warm temps in California, offshore and downslope flow over the Cascades, warming over our region. Notice the development of the "thermal" trough into western Oregon and Washington....the classic warm weather pattern.
Western Washington should surge into the mid-70s tomorrow and mid-80s on Wednesday and Thursday. Impressive for late September! And I have no plans to return to California where temperatures of purgatory will abound. A heat warning is up for the SF Bay Area where some interior locations will get well into the 100s. Yosemite Valley will be in the mid 90s.
And don't forget the Willamette Valley...where temperatures will climb into the 90s. The Willamette is often 5-10F warmer than the western Washington interior...frequently even warmer.
Posted by Cliff Mass at 10:25 PM