As the U.S. marks the first official day of summer and the longest day of the year, the American Southwest is being punished by a near-unprecedented heatwave.
Temperatures could reach 121 degrees Fahrenheit Monday. Four people died as a result of the heat over the weekend. On Sunday, it was 115 degrees in Tucson, Arizona, and 118 degrees in the valley city of Phoenix, the state's largest city and state capital.
The Phoenix temperature beat the previous record of 115 degrees for this point in the year set 50 years ago, according to the National Weather Service.
"When a ridge of high pressure like this one forms in the middle to late June, it can deliver some of the hottest weather possible to the Desert Southwest," AccuWeather Western U.S. Expert Ken Clark said.
"The peak of the heat in many areas will be on Monday, but Tuesday will be no slouch either in the high heat department," Clark said.
See photos of the Southwest under scorching temperatures
The forecast had been for temperatures to reach as high as 120 in Phoenix over the weekend, which did not officially occur. But Yuma, Arizona, in the southwestern portion of the Grand Canyon State, saw temperatures at that level. Weather service meteorologist Andrew Deemer said he had "no doubt there are places in the Valley (near Phoenix) that hit 120 or so."
Two of those who died over the weekend from heat-related causes were hiking on trails near the two cities.
United Flight 6186 flying from Houston to Phoenix Sunday was rerouted because of heat-related concerns.
Wildfires are also being fueled by high temperatures. A Santa Barbara, Calif., blaze that began last week has continued Monday, and a new wildfire has begun 200 miles to the south in Potrero, Calif., near the Mexican border.
Temperatures in Los Angeles exceeded 100 degrees and Burbank, Calif. temperatures reached 105 degrees. A wildfire occurred in a Los Angeles neighborhood, as well. The San Fernando Valley saw temperatures close to 110 degrees, and the inland desert region of Palm Springs hit 115 degrees.
Las Vegas is forecasted to hit 113 degrees Monday.
The highest forecast is for Death Valley, Calif., traditionally considered the hottest spot in the United States. Those in that region could experience temperatures as high as 125 degrees, according to AccuWeather. Death Valley is home to the hottest temperature ever recorded in the U.S., 134 degrees on July 10, 1913.