- Massive heat wave spreading from California, Arizona, New Mexico into the Rockies
- Heat warnings issued for parts of Utah
(CNN)The Southwest's lethal heat is on the march.
After welcoming the start of summer with record temperatures, the heat's spreading from California, Arizona and New Mexico into the Rockies.
Heat warnings have been issued for parts of Utah and red flag warnings -- indicating conditions are ripe for wildfires -- are in effect from Montana south into Colorado, CNN meteorologist Dave Hennen said.
As the heat grows out West, so does the threat for severe weather, from the nation's mid-section out to the East Coast.
About 22 million people, in an area that stretches from the northern Plains to the Mid-Atlantic, face a higher risk of severe weather Tuesday, Hennen said, a threat that will only increase Wednesday in places like Chicago and Milwaukee, where they'll be a high risk of tornadoes possible.
The record-setting heat has been deadly in Arizona, where five people -- two in Phoenix and three near Tucson -- were killed over the weekend, authorities said.
In Phoenix, a 28-year-old woman died Sunday and a 25-year-old man died Saturday -- both while hiking, according to Larry Subervi, a Phoenix Fire Department spokesman.
Pima County Sheriff Chris Nanos said at a news conference Monday that two hikers died Sunday near Tucson and another is missing.
A search was suspended Monday to protect searchers from the heat, but is expected to resume Tuesday, CNN affiliate KGUN reported.
"It's just too dangerous for my team to be out here," Nanos said.
It was so hot, a woman in her 50s died of heat exposure while going for a walk in the middle of the city, Nanos said.
Nanos urged people to stay indoors for their safety -- and for the safety of others.
"If not for your own safety, [then stay inside] for the safety of my team and these volunteers who come out here and do this all the time," he said. "This week, until these temps come down, get your exercise at home. Get your exercise indoors. Or just stay inside. It's too hot."
A map from the National Weather Service shows the parts of the United States that are currently under heat advisories (pink areas face excessive heat warnings, while areas in orange face heat advisories).
Much of the current heat wave can be attributed to a so-called heat dome -- a pattern that can lead to record-setting temperatures and heat waves -- according to CNN Meteorologist Rachel Aissen. A heat dome occurs when air is capped by the upper atmosphere in the same location: The air hits the cap and returns to the surface, continuing to heat it like a convection oven.
Swarm of wildfires
More than a dozen wildfires have popped up throughout the region as of late Monday.
Three of them had scorched more than 30,000 acres by the end of the day:
Three other significant fires are burning in the trio of states as of early Tuesday:
Another wildfire popped up in the San Gabriel Canyon near Los Angeles on Monday, quickly consuming about 1,500 acres.
Billowing smoke could be seen from nearby Dodger Stadium.
CNN affiliate KCBS reported that in addition to that blaze, which is being dubbed the Reservoir Fire, another fire started nearby in Fish Canyon.
The so-called Fish Fire has consumed 3,000 acres and has not been contained at all, according to LA County Fire officials.
Also in the Los Angeles area, the city of Burbank -- which is home to Warner Brothers and Walt Disney studios -- hit 111 degrees Fahrenheit, setting a new record, according to the National Weather Service.
The hottest temperature recorded in the United States on Monday also came in California, but further north. It was 126 degrees in Death Valley, the NWS said.
Elsewhere in California, evacuations were ordered in San Diego County as fires continue to rage near the U.S.-Mexico border. And a large wildfire in Santa Barbara County also forced mandatory evacuations.
CORRECTION: A previous version of this story incorrectly stated the number of hikers who had died.