Sweltering heat continued to permeate the western United States on Thursday, as forecasters warned that some desert communities could see temperatures soar to 117 degrees.

The extreme heat is expected to span a wide swathe of the country — both within and beyond the West. Parts of Arizona, Nevada, New Mexico, Texas, Arkansas and Florida are all forecast to see triple-digit or near-triple-digit temperatures through at least the end of the week, according to the National Weather Service.   

The hottest conditions are expected in southern California’s Coachella Valley, including the city of Palm Springs, which could see dangerously high temperatures of 117 degrees on Thursday and Friday. 

Particularly dangerous heat has lingered in Arizona, with temperatures reaching 113 degrees in Phoenix on Monday, Tuesday and Wednesday — and not dipping below 90 degrees. Temperatures could creep up to 115 degrees by midday Thursday, and might not fall below 110 degrees in the Phoenix area before next week, according to forecasters.    

The weather service has issued extreme heat warnings and advisories for millions in the desert Southwest, and portions of the Southeast, which were scheduled to remain effective until Friday night. 

Extreme heat watches have also been preemptively issued for parts of Colorado, Montana and the Dakotas, since they were slated to bear the brunt of the warmth once it spreads this weekend through next week.

Extreme heat has closed hiking trails in the Phoenix area and prompted a surge of emergencies, with the Phoenix Fire Department telling “CBS Mornings” it has responded to about 400 heat calls since May 1.

Phoenix Fire Captain John Prado said firefighters had already responded to two heat stroke emergencies and once utilized the department’s “cold water immersion” strategy, which aims to rapidly lower the body temperature of a person suffering a heat-related emergency. He said emergency responders were using the technique “daily, across the entire city.”

Eighteen people in the Phoenix area have died so far this year from heat-related issues, according to local officials, who said that figure was much higher than the five heat-related deaths recorded by this time last year.      

“Heat related illnesses increase significantly during extreme heat events,” the National Weather Service said. “Overexposure can cause heat cramps and heat exhaustion to develop and, without intervention, can lead to heat stroke.”

Fire weather alerts were in place, too, for parts of the region, through Thursday. CBS News meteorologist Nikki Nolan said dry thunderstorms and low relative humidity increased risks of wildfires, noting how lightning strikes could spark flames in an area with little rain to extinguish them.  

Heat was also scorching stretches of the Southeast, with forecasters in the Carolinas warning of potentially extreme conditions in both states, as well as Georgia, through the end of the week. Heat indices, which account for temperature and humidity readings, could reach 113 to 116 degrees in those areas, the National Weather Service said.