Looking at Portland's record-breaking heat dome four years later
PORTLAND, Ore. (KOIN) — Four years ago, the Portland metro area endured the most extreme heat wave in city history.
In June 2021, a strong and anomalous ridge of high pressure settled over the Pacific Northwest, bringing deadly and record-shattering temperatures to the region.
On June 26, 2021, Portland recorded a high temperature of 108°F, a new all-time record high. The very next day, temperatures soared to 112°F. Then, on June 28, Portland topped out at 116°F.
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The heat wave expanded across the region for five days. Two days sat above 90 degrees, with the three record-crushing days above 100 degrees. The historic event was most intense from June 26-28.
Before 2021, Portland's hottest day on record was 107°F set back in 1981. The heat wave, also caused by and called a 'heat dome', not only broke that record, but it did so three days in a row in the unprecedented heat up.
A heat dome can develop when a strong ridge of high pressure traps heat in the upper levels of the atmosphere. It can persist for days and cause extreme temperatures and heat waves to form.
During the 2021 heat dome, Multnomah County recorded 72 deaths due to the extreme heat.
As a result, and with the heat still fresh in Portland's mind, the city has worked to prevent future disasters in case of extreme heat.
In 2024, Multnomah County, alongside Washington and Clackamas counties, shared the results of a heat mapping project, which found that not all areas of the city experience heat evenly.
The project tracked temperatures around the counties, finding a disparity of 17 degrees between the hottest and coolest locations around an area covering 400 square miles.
The study found that areas near highways and places with fewer trees experienced higher temperatures, while more rural locations or places with more tree canopy, like Firest Park, experienced lower temperatures.
During the heat dome, the Pacific Northwest reached such high temperatures that climate scientists later determined similar events typically only happen once in every 10,000 years.
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