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It has been two years since the historic parked over the Pacific Northwest during the last week of June, soaring temperatures well past all-time record highs.

A ‘heat dome’ is a strong high-pressure system aloft that gets cut off from the main westerly flow around the Northern Hemisphere, in this case across the Northern Pacific Ocean. This system’s sinking air motion and resulting low-level offshore flow toward the Pacific produced blistering temperatures. As an analogy, think of this upper level high as a large rock in a river, resting in one spot while the water flows around it.

The descending air in a heat dome creates a warmer and warmer air mass over time. From June 25 thru June 28 in 2021, temperatures in the region warmed each day, peaking on the 28th, crushing previous all-time record highs. Bellingham soared to 99 degrees, Everett Paine Field 100, Arlington 103, Sea-Tac Airport 109, Olympia and Forks 110, and Portland, Ore. a scorching 116 degrees.

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During this historic heat wave, over 250 people succumbed to the heat in the Pacific Northwest, and in Western Canada, over 400 people perished. Excessive heat is the number one weather-related hazard yielding fatalities in the world. In fact, it kills more people than all other weather-related hazards like hurricanes, floods, tornados, and winter storms combined.

At the recent Pacific NW Weather Workshop, a presentation highlighted this heat dome event as an extreme anomaly.

Yet with the ongoing warming of the planet, the global upper-level air pattern has been tending to produce more of these cut off upper-level highs that create extreme heat waves. For instance, Texas is suffering through one such event this week as well as parts of India. Earlier this spring, Western Europe had a similar heat wave.

Looking forward to the rest of this century with the ongoing warming of the planet, this kind of intense heat event can no longer be totally ruled out.

The latest summer weather seasonal outlook continues to tip the odds toward warmer and drier conditions than average through September across Western Washington. The odds of another extreme heat dome are quite slim this summer, but not zero – kind of like rolling snake eyes three times in a row.