Authorities from Oregon to British Columbia are investigating hundreds of deaths in connection to the historic heat wave in the Pacific Northwest corridor.

Temperatures in Oregon topped 117 Monday, according to the National Weather Service, due to a heat dome trapping hot air over the state and its neighbors. 

At least 63 people have died since Friday, the State Medical Examiner’s office said, and “preliminary investigation suggests may be associated with the Pacific Northwest heatwave,” said Oregon State Police Captain Tim Fox. 

That number was based on reports from each county’s medical office and could fluctuate as more information becomes available. 

At least 45 of those deaths were in Multnomah County, which houses Portland,