California Gov. Gavin Newsom declared a state of emergency for counties threatened by the dangerous Fairview and Mosquito Fires Thursday, as firefighters across the drought-ravaged western U.S. battled scores of wildfires in the searing heat.

Driving the news: Both the deadly Fairview Fire in Riverside County and the Mosquito Fire in El Dorado and Placer counties that jumped a river Thursday are "threatening multiple communities and critical infrastructure, forcing the evacuation of tens of thousands of residents," per Newsom's statement.

Threat level: As more critical fire weather threats were expected across the western Pacific Northwest on Friday, 71 large fires were burning across eight states, mostly in the western U.S., according to the latest information from the National Interagency Fire Center (NIFC).

What's happening: Southern California's Fairview Fire, which has killed two people, has swollen to more than 27,300 acres since igniting Monday and was at 5% containment. Mandatory evacuation orders were in effect for several neighborhoods.

What we're watching: Southern California Edison tweeted Thursday that "public safety power shutoffs" may be required due to the extreme heat and fire risk. The utility's website indicated most customers that could be impacted lived in Los Angeles, Riverside and Orange counties.

Coastal Oregon and Washington face the threat of scorching heat and dangerous fire weather this weekend and expansive red flag warnings have been issued.

Meanwhile, hazardous weather associated with Hurricane Kay's remnants was expected to begin entering southern California and parts of the Desert Southwest on Friday, with heavy rains, powerful winds and flash flooding expected.

By the numbers: The intensity of this year's fire season has been above the 10-year averages, with more than 49,300 fires so far burning over 6.3 million acres across the U.S., per the NIFC.

The big picture: Human-caused climate change is projected to make heat waves and elevated temperatures hotter, more expansive and longer lasting in parts of the U.S., which is expected to exacerbate drought conditions across the country and escalate wildfire intensity, frequency and size.

Editor's note: This article has been updated with new details throughout.