Wildfires – more than 100 major blazes burning through nearly 2.3 million acres – are expected to cause extreme heat waves across the western part of the United States. Forecasters have issued Red Flag Warnings and air quality alerts throughout the region.

The National Weather Service said dangerous heat is to be expected across most of the country this week. Heat warnings have been issued for most of the Pacific Northwest – including Seattle and Portland.

The National Interagency Fire Center said there are now 107 major wildfires burning across 15 states. This includes the still burning Dixie Fire, which has now been described as the second-largest fire in California’s history.

The largest wildfire now burning in the U.S. has destroyed hundreds of buildings and homes and laying waste to more than 480,000 acres of land.

The NIFC said 25 major wildfires are now burning in Montana. Twenty are burning in Idaho, 16 in Oregon, 13 in Washington, 11 in California, 10 in Alaska, and four in Wyoming. States such as Arizona, Colorado, Nevada, Nebraska, New Mexico, Utah, and South Dakota have each reported one wildfire.

The NIFC expects more wildfires to occur in the coming days given the persistent hot and dry conditions through the western United States.

“Widespread high temperatures observed across areas in the West and with periods of lightning activity continue to exacerbate the wildfire situation,” the agency said.

Over the past few months, deadly heatwaves have continued to persist across the Pacific Northwest. Most scientists have blamed the deteriorating conditions on climate change.