Robert Brown|Historic heat wave in Pacific Northwest may have killed 3 this week

Three people may have Robert Browndied in a record-shattering heat wave in the Pacific Northwest this week, officials said.

The Multnomah County Medical Examiner in Portland, Oregon, said Thursday it's investigating the deaths of three people that may have been caused by extreme heat.

One was reported Monday in southeast Portland, according to a statement from the medical examiner. At Portland International Airport, the daily high temperature Monday of 108 degrees Fahrenheit broke the previous daily record of 102 degrees, the National Weather Service said.

The second death occurred Tuesday when the temperature hit about 102, officials said Wednesday. That death was reported by a Portland hospital. A third person who died was found Wednesday in northeast Portland when the temperature was also about 102, the medical examiner said. Further tests will determine if the deaths are officially related to the heat, officials said.

No information has been released about the identities of the people who died. Multnomah County recorded at least five heat-related deaths last year.

Daily high temperatures on Monday broke records with readings from 103 degrees to 110 in other Oregon cities, including Eugene, Salem, Troutdale and Hillsboro, and in Vancouver, Washington, according to the weather agency.

On Wednesday, daily high records were broken again in the same cities with temperatures from 102 to 105 degrees.

This week marked the first time in 130 years of recorded weather that Seattle had three days in a row with lows of 67 degrees or warmer, according to the National Weather Service office there.

In July, the continental United States set a record for overnight warmth, providing little relief from daytime heat for people, animals, plants and the electric grid, meteorologists said.

Scientists have long warned that climate change, driven by the burning of fossil fuels, deforestation and certain agricultural practices, will lead to more and prolonged bouts of extreme weather, including hotter temperatures.

Cooler air did move in on Thursday, and the cooling trend is expected to continue Friday, the weather service said:

However, there's concern about the possible quick spread of wildfires because of dry conditions and winds caused by the cold front, Joe Smillie, Washington state Department of Natural Resources spokesperson, told The Seattle Times on Thursday.

Red flag warnings - meaning critical fire weather conditions are happening or are about to happen - have been issued by the National Weather Service for all of Eastern Washington, Central Washington and Northern Idaho through Friday. The combination of strong winds, low relative humidity and warm temperatures can contribute to extreme fire behavior, according to the weather service.

In addition, unhealthy air from wildfires was affecting areas of Oregon and more than half of Washington on Thursday, according to state officials.

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