A very strong ridge of high pressure is entrenched across the West Coast, bringing a steady diet of heat and sunshine to Western Washington.
And it's not budging for a while.
With a very hot air mass in place and plenty of sunshine, high temperatures across the Puget Sound region will be in the upper 80s to low 90s for at least the next week. And there is not much relief expected at night as overnight lows are only forecast to drop into the mid 60s.
As a result, the National Weather Service has issued a Heat Advisory for much of the Puget Sound region throughout the weekend and into Monday morning.
The weather pattern is similar to what we saw in July last year that brought a string of four consecutive 88-degree days in Seattle. High pressure has built across the West, but importantly, it is centered just to the east of the Cascades. That is preventing an east wind from developing across the Puget Sound region which would have made high temperatures significantly warmer -- perhaps even upper 90s to near 100.
But being near the center of the ridge, it also doesn't allow much in the way of our cooling ocean breezes to make any inland headway, leaving Seattle to bake in a somewhat stagnant hot air mass.
To put it another way: Imagine Seattle is sitting inside a home on a warm, summer day. The marine breezes would be akin to turning on the air conditioner and keeping things comfortable. An east wind would be akin to turning on the heater and... not making things more comfortable. But the current pattern with no wind (aside from a late day light seabreeze) is essentially neither -- the home bakes in the sun and opening the windows isn't helping much because there is hardly any wind outside. Welcome to 88-91 degrees, Seattle.
It's even hotter to the south and east where the air mass is even hotter. Eastern Washington will have highs breaking 100 degrees in places. Oregon is baking under the same heat with highs in the mid to upper 90s forecast in Portland, Salem and Eugene -- special note for those of you taking part in the Seattle To Portland bike ride that you will be dealing with much hotter temperatures than usual.
But since we don't have the east wind, there is relief to be found with a few hours' drive. The coast and along the Strait of Juan de Fuca will be spared much of this heat blast as there will just be just enough of a trickle of evening ocean seabreezes to keep highs in the 70s. (East wind days have them baking in the 80s and even low 90s too but they dodge that bullet this time around.)
Hikers take note there is also a chance of thunderstorms in the Cascades on Saturday and Sunday afternoon and evening.
When does it end?!?!?
Knowing that upper 80s/low 90s is beyond the comfort level of a vast majority of the region's residents, especially in limited air conditioning Seattle, the news is not the best. Forecast models suggest this pattern is essentially stuck until well into next week, with perhaps slight cooling Thursday but no significant cooling until Friday.
Friday will mark Seattle's sixth-consecutive day at 80 or warmer and this will likely being the longest stretch of 80+ days since a 15-day stretch in 1977.