Millions of Americans are under heat warning due to extremely high temperatures in the Plains and Northeast, according to maps.

This week, a heat dome that is scorching the western region of the country is spreading to the Northeast, affecting some 100 million people nationwide.

The deadly heat was felt throughout the Great Basin, the Rockies, and parts of the desert Southwest on Sunday, when temperatures in Billings, Montana, reached a record high of 111 degrees.

Maps show latest heat wave

According to CBS News meteorologist Nikki Nolan, temperatures are expected to be 20 to 30 degrees above typical for this time of year. Throughout the week, temperatures in some places will break records.

The Northern Tier is predicted to reach its high on Tuesday, and the Northeast is predicted to reach its peak on Wednesday.

Over the coming days, the region’s heat index is expected to rise from the high 90s to over 100.

The National Weather Service reports that temperatures in Salt Lake City reached an all-time high of 109 degrees on Sunday. The previous record, set in 1960, 2002, 2021, and twice in 2022, was 107 degrees. An severe heat warning was in effect for the majority of Utah and was expected to last until Tuesday morning.

Forecasters issued excessive heat warnings for large portions of both states as the heat expanded into the Dakotas.

Even in mid-July, forecasters cautioned about the risks connected to the unusually lengthy period of heat, which they have described as “exceptionally rare” for some places. Hazardous heat would occasionally move eastward while remaining in that central area into the following weekend, according to the National Weather Service.

The heat dome, an atmospheric phenomenon that basically traps hot air over a certain area, was constructed in the West following last week’s start of the summer’s first heat wave. Forecasters now advised residents to prepare for widespread temperature highs between 105 and 115 degrees, which would break multiple local temperature records and raise the risk of wildfires. Additionally, they issued a warning about the increased risk of heat-related ailments, such as heat stroke.

“Due to little relief, extremely hot daytime highs and possibly record-warm lows could cause heat stress to worsen over the next days, according to a weather service advisory.

Heat fuels wildfires, fires up thunderstorms

In California, the Summit Fire in the Antelope Valley temporarily forced people outside Los Angeles to evacuate as it burned nearly 3,000 acres. The Los Angeles County Fire Department said crews made significant progress on the blaze, with containment at 31% as of Sunday evening, CBS Los Angeles reported.

Extreme heat is expected over parts of Southern California and into Arizona through Thursday, according to Nolan. Temperatures are forecast to reach into the 90s and 100s, especially in the desert Southwest.  Overnight temperatures were forecast to be record-breaking in Southern California, but the Southwest wasn’t expected to break records, Nolan said.

Two wildfires were sparked on Sunday in Colorado’s high country even as firefighters continued to battle the Aspen Acres Fire, which had burned more than 850 structures, including hundreds of homes.

Sen. John Hickenlooper, a Colorado Democrat, toured the damage this week and said the state needs more funding to battle wildfires.

“There have been huge cuts to the fire service, to the BLM [Bureau of Land Management], there’ve been cuts everywhere,” Hickenlooper said.

Rain and flood risk

Heavy rain storms and flooding are a concern in parts of the South. In Louisiana, thunderstorms dumped several inches of rain on New Orleans, forcing families to wade through knee-high water.

Also on Saturday, hundreds of people were rescued amid historic flash flooding in Missouri. Rescue crews airlifted more than 200 people stuck at a children’s camp after 6 to 12 inches of rain fell in the southeastern part of the state.

Farther east, communities in the Philadelphia area were cleaning up after powerful microbursts ripped through neighborhoods with gusts up to 70 miles per hour.  Mayor Cherelle Parker signed a Declaration of Disaster Emergency on Sunday, CBS Philadelphia reported.