The wheels are in motion to build a rather significant, and possibly historical heat wave over the Pacific Northwest starting today.
A big ridge of high pressure is building in, and with it comes a very strong thermal trough <http://www.komotv.com/weather/faq/4307787.html>. That will spin our low level winds from the west, which brings in cool air off the ocean, to the east, which comes from the dry interior, and further gets heated when it sinks and compresses coming down the western slopes of the Cascade Mountains. Thursday will begin with areas of fog, but sunshine wins out by late morning for all areas. Highs will vary a bit as the thermal trough builds. The coast will actually be one of the warm spots, with highs into the low 80s. In the Puget Sound region, locations close to the water and the North Sound will get a bit of a northerly breeze in the afternoon, limiting high temperatures to the low-mid 70s, but away from Puget Sound you'll nudge up against 80 too.
The heat is on full blast for Friday, with highs across the region in the mid-upper 80s, with perhaps some 90s in the foothills. We begin cranking up the natural air conditioning on Saturday, where the coast will cool off first to the 70s. But inland, it's another scorcher, with highs in the mid-upper 80s again, although maybe a bit of a cooling breeze in the late evening that might make the official highs a degree or two cooler. The winds shift to more of the west for Saturday night and Sunday, but signs now point to this being more of a gradual cool down instead of the big 35 degree drop we sometimes see. With that variability, Sunday's high temperature remains difficult to peg, but we're going to warm it up to the mid 70s over what we had yesterday. Still, there's quite a range it could end up being - from about 70-80 at this rate. Further cooling occurs Sunday night into Monday, where Monday's highs will be closer to the upper 60s/near 70 with perhaps even some morning clouds and fog.
Jim Castillo
KOMOTV Meteorologist
