A massive heatwave is sweeping through the Pacific Northwest, which is known for its relatively moderate climate. The heatwave has increased temperatures to record highs and driven people to beaches, pools, and air-conditioned malls.

Areas around Portland recorded temperatures of as much as 112 degrees Fahrenheit, while those in Seattle hit 104 degrees. Over the past three days, the typically overcast city of Seattle recorded temperatures above 100 degrees for the first time. Temperatures in Washington State surpassed previous records, reaching 115 degrees Monday.

Outside the major cities in the Pacific Northwest region, temperatures climbed even higher. In north-western Oregon, temperatures exceeded 118 degrees. Spokane, Wenatchee, and Pullman also experience record-breaking overnight temperatures.

According to the National Weather Service, the heatwave is being caused by two pressure systems – one from the Aleutian Islands and the other from Hudson Bay.

“The Pacific north-west got caught in a region where a series of feedbacks set up these very warm temperatures – no, hot temperatures – with very little cloud cover and very warm temperatures at night too,” the NWS’s Weather Prediction Center said.

The agency said that the heatwave can be described as a “heat dome” covering the region. The agency said such events don’t happen often, usually occurring only once every two to three decades.

The temperatures experienced by the Pacific Northwest are not the worst in the country. However, people living in the area aren’t used to high temperatures, which may cause health problems for some people.