While the focus lately has been on the recent heat along the East Coast and parts of the Southeast, areas along and near the West Coast in the Pacific Northwest are going to begin to really heat up, especially today, tomorrow and Saturday. Excessive heat warnings have been issued through Saturday from western Washington state, including Seattle, down into western Oregon, including Portland. For most areas directly on the coast, heat advisories have been issued and extend down into northern California.
Typically, coastal areas in the Pacific Northwest have moderated temperatures thanks to the Pacific Ocean and onshore flow. This keeps milder temperatures west of the Cascades even during the summer months. Although it can definitely get cold at times in these same areas during the winter, this same scenario keeps temperatures milder during the winter months than they otherwise would be.
A thermal trough is going to build into the Pacific Northwest generally west of the Cascades and strengthen today and tomorrow. To give you a visual of this, take a look at the two images below. The mean sea level pressure will lower along the Pacific Northwest coastal regions today, and as the thermal trough builds further into the region, the surface pressure will drop even further on Friday. Also notice strong surface high pressure building into Montana building behind a mid to upper level trough that will be bringing much cooler temperatures east of the Pacific Northwest.
This kind of setup changes the overall wind flow at and near the surface. Instead of getting the typical onshore flow (winds moving from from the ocean to land), it will switch to an offshore flow (winds moving from the land to the ocean). Since the Cascades extend from Washington down to northern California, this will enhance warming even further as air will get forced up those mountains and back down the other side, and due to adiabatic processes (not going to elaborate on that), the air will warm as it is forced down the ocean-facing mountain slopes.
At or near the surface, wind flows from areas of high pressure to areas of low pressure. The map below shows the direction the wind will be blowing near or right above the surface. As you can see, it’ll be blowing from northeast to southwest, and at times, even directly east to west. This is a recipe for really hot temperatures this time of year along and west of the Cascades.
In addition to all of this, mid-to-upper level ridging extends along the West Coast into western Canada. This will further enhance those really hot temperatures.
What To Expect?
Temperatures will soar well into the 90s just inland, possible even reaching 100 degrees or slightly higher in places. Temperatures directly on the coast (from the northern half of Oregon into Washington) will likely reach the mid to upper 80s today and Friday, with some areas possibly hitting 90. Friday should be the hottest day with Saturday being a bit better for areas directly on the coast.
These are projected temperatures for Friday at the time of peak heating and below that, are projected temperature anomalies (departures from average temperatures). Records could definitely be broken across these areas!