Surprise Thunderstorms Cap Off A Record Heat Wave

I’m writing from the front porch of an old fishing cabin in Sekiu, a small fishing village along the Strait of Juan de Fuca approximately 15 miles ESE of Cape Flattery. I’m being treated to an incredible – and unexpected – lightning show from some strong thunderstorms to our north over the Strait and Southern Vancouver Island.

Credit: University of Washington
Credit: Blitzortung Lightning Network
Infrared satellite at 10:55 pm 8/16/2020 showing thunderstorms over the Strait of Juan de Fuca and Central/Eastern WA south to the Sierra Nevada
Credit: College of Dupage

I’m on a fishing trip up here with my family this week and just arrived tonight, so between packing in the morning and traveling in the afternoon/evening, I hadn’t paid much attention to the evolving weather forecast. I knew that today was going to be hot and that there was the potential for a few thunderstorms drifting into the Puget Sound lowlands, but I never imagined that we’d see anything as spectacular as the show we’ve seen tonight.

These thunderstorms occurred because we had a decent amount of low and mid-level instability ahead of a developing upper-level shortwave trough. This shortwave trough provided the dynamic lift to initiate these storms, and the hot, moist unstable atmosphere contained approximately 500-1000 J/kg of elevated CAPE (convective available potential energy) to fuel these storms.

Most-unstable CAPE (MUCAPE) at 10pm 8/16/2020
Credit: Storm Prediction Center

Although the surprise lightning stole the show this evening, the extraordinary warmth experienced throughout the Pacific Northwest (especially over Western Washington) was no less impressive. Sea-Tac measured a high of 98 degrees, its warmest reading since the all-time record high of 103 recorded back on 7/29/2009. And our moist, southerly flow only made things feel hotter. On the other hand, Portland and the Willamette Valley “only” hit the mid 90s today instead of the upper 90s/low 100s that were forecast due to smoke from fires over Northern California reducing the amount of solar heating during the day.

Temperatures at 5pm 8/16/2020
Credit: NWS

Monday and Tuesday will see light onshore flow, so we’ll remain much warmer-than-average but will no longer be in record territory. Onshore flow strengthens Wednesday/Thursday, and a weak system may even bring a few showers to the coast on Friday.

Hope you enjoyed the lightning show as much as I did!
Charlie

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