Heat advisories are in effect for more than 25 million people in California, Nevada, Arizona, Utah and New Mexico as temperatures soar across parts of the US. Driving this prolonged, unseasonable heat is a robust heat dome — a large area of high pressure that parks over an area, traps air and heats it with abundant sunshine for days or weeks. Several temperature records were broken Thursday across states including California, Arizona and Nevada. Las Vegas reached 111 degrees, topping the record of 110 degrees set in 2010. In California, a high of 122 degrees in Death Valley broke a record set in 1996. Phoenix also set a record high of 113 degrees, with more triple-digit temperatures expected today.