When will 2021’s ‘Heat Dome’ return to summer in Seattle?

Jun 25, 2024, 6:43 AM

heat dome...

Western Washington receiving some much-needed sunshine this week. (Photo courtesy of Getty Images)

(Photo courtesy of Getty Images)

June 25 through June 28, 2021. As the song went from Disney’s “The Little Mermaid,” it was hot, hot, hot!

It has been three years since the historic “heat dome” parked over the Pacific Northwest during the last week of June, surging temperatures well past record highs.

More on PNW’s 2021 heat dome: ‘Only going to get hotter,’ heat wave blasts Northwest

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 ocean produced the blistering temperatures. As an analogy, think of this upper-level high-pressure system as a large rock in a river, resting in one spot while the water flows around it.

The descending air in a heat dome over time creates a warmer and warmer air mass. During June 25-28, 2021, temperatures in the region warmed each day, peaking on July 28 and crushing previous record highs. Bellingham soared to 99 degrees, Everett Paine Field hit 100, Arlington reached 103, SeaTac Airport climbed all the way to 109, Olympia and Forks got up to 110 and Portland, Oregon reached a scorching 116 degrees.

During this historic heat wave, more than 250 people in the Pacific Northwest succumbed to the heat. In Western Canada, more than 400 people perished. Excessive heat is the No. 1 weather-related hazard-yielding fatality in the world. In fact, it kills more people than all other weather-related hazards — including hurricanes, floods, tornados and winter storms — combined.

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 high-pressure systems that create extreme heat waves. For instance, much of the middle and eastern parts of the U.S. have suffered through a heat wave in recent days, as well as parts of India where temperatures have exceeded 120 degrees.

Looking forward to the rest of this century with the continuing warming of the planet, this kind of intense heat event for the Pacific Northwest can no longer be totally ruled out. The odds of another extreme heat dome in this region are quite slim this summer, but not zero – kind of like rolling snake eyes three times in a row.

Fortunately, the latest seasonal weather outlook for Western Washington released last week reflected a change from the earlier warmer and drier conditions expected through September. With more heat anticipated well inland for much of the rest of the nation, that weather pattern is expected to induce more of nature’s air conditioning from the Pacific Ocean with onshore flow, moderating temperatures.

The latest seasonal weather outlook for Western Washington now shows around average temperatures and precipitation through September. The outlook offers the overall conditions and does not mean there will not be hot spells or cooler-than-average conditions at times. The close-to-average precipitation is also better news regarding the risk of wildfires and wildfire smoke. The threat of wildfires remains during normally the driest time of the year and the recent fire near the Skagit and Snohomish County line demonstrated that danger.

If sensitive to excessive heat, here are some precautions to help during a period of hot weather. Be sure to stay hydrated by drinking plenty of water. Spend time in an air-conditioned location to help relieve the stress of the heat. If outdoors, seek shade and use sunscreen to avoid sunburn. During the heat of the day, avoid strenuous activities like running. If working outdoors, take breaks in shade and drink plenty of water.

Avoid leaving children and pets in cars, even for just a few minutes. Wear light, loose-fitting clothing to help reflect heat. If on area waterways, be sure to wear a properly fitted life jacket to avoid falling into the cold water and suffering cold water shock, potentially drowning as a result. And for meals, eat easy-to-digest foods like salads and fruit.

Be sure to check on elderly family members, friends or neighbors to help ensure they are doing okay during hot weather, particularly if they take medications. Studies have revealed that common treatments such as heart medicines, antihistamines, and decongestants don’t mix well with heat. Continue to take the medications, just stay cool, and stay hydrated. Consult with a doctor for any concerns.

More on local weather: What does this week’s weather look like post-summer solstice?

Always monitor the latest weather forecasts for the potential of any heat waves. The National Weather Service has a publicly available heat-related resource called HeatRisk. This resource is a color-numeric index that shows a forecast threat of heat-related impacts. HeatRisk takes into consideration how unusual the heat is for the time of year, the days of the expected hot weather including not only daytime temperatures, but also temperatures overnight, and the elevated risk of heat-related health impacts.

HeatRisk has been tested in the Western U.S. for a number of recent years including the Seattle Forecast Office and this year, was expanded nationwide. The resource has been quite useful during the recent heat wave across much of the eastern two-thirds of the country. Many TV weather segments have placed colorful heat graphics on screen, highlighting areas of risk.

Enjoy this summer; just do so safely, particularly during periods of hot weather.

Ted Buehner is the KIRO Newsradio meteorologist. You can read more of Ted’s stories here and follow him on X, formerly known as Twitter.

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When will 2021’s ‘Heat Dome’ return to summer in Seattle?