It's bringing record highs to the Pacific Northwest. What is a heat dome?

  • On Sunday, Portland hit 112 degrees, and Seattle reached 104. A rare heat dome was to blame.
  • There is no timetable for how long a heat dome can last.
  • Heat domes have occurred more frequently as global temperatures have increased over the years.

Much of the Pacific Northwest is currently experiencing some of the highest temperatures in the region's history.

Portland reached 112 degrees on Sunday, the city's highest temperature since the National Weather Service started keeping records in 1940. And Seattle hit a record high of 104 degrees the same evening, according to the National Weather Service.

It got so hot on Sunday that the U.S. Olympic track and field trials in Eugene, Oregon had to be postponed until 8:30 p.m. PT.

So why is the Pacific Northwest dealing with extreme temperatures right now? It's because of a heat dome.

What is a heat dome?

No, there is no invisible dome over the United States. But a heat dome occurs when there is "a strong change (or gradient) in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter," according to the National Ocean Service

The warm air coming from the west part of the Pacific Ocean then gets trapped in the jet stream as it approaches land. When that hot air arrives over land, the atmosphere traps the hot air as if a lid was put on it. Winds can move the heat dome around, which is why it can also be referred to as a heat wave.

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How long does a heat dome last?

There is no timetable for how long a heat dome can last, but things won't immediately cool down in much of the Pacific Northwest. Forecasts have inland areas such as Spokane, Washington and Boise, Idaho reaching triple-digit temperatures for the rest of the week. The National Weather Service's excessive heat warning is in effect until 11 p.m. PT on Thursday.

People gather at the Sandy River Delta near Troutdale to cool off during the start of what should be a record-setting heat wave on June 25. The Pacific Northwest sweltered Friday as a historic heat wave hit Washington and Oregon, with temperatures in many areas expected to top out 25 to 30 degrees above normal in the coming days.

How rare is a heat dome?

Heat domes have occurred more frequently as global temperatures have increased over the years. However, this specific heat dome is one of the rarest.

Jeff Berardelli, a CBS News meteorologist, tweeted on Sunday the chances of experiencing this heat wave is a 1 in 10,000 chance.

Does global warming play a role?

Climate change has seen temperatures rise across the planet, and the increased frequency of heat domes is a product of that. 

"Global warming is greatly increasing the odds of experiencing unprecedented heat extremes," said Daniel Swain, a climate scientist at UCLA, in a recent blog.

It won't be the last time we see temperatures rise in the United States this year either. A three-month projection done by the National Weather Service for July-September shows much of the country will experience higher temperatures, with the most extreme highs occurring in the Northeast.

Follow Jordan Mendoza on Twitter: @jord_mendoza.