The mercury will skyrocket later this week across a large portion of the western U.S., especially the Southwest, as an impressive high-pressure ridge aloft builds and expands. When this occurs, the air sinks and warms, and the result is very few clouds and extremely high temperatures. The highest temperatures of the season will be felt across a large area. The brunt of the heat will be felt from the Central Valley of California, through much of the Desert Southwest, and across the Great Basin.

The National Weather Service has already issued excessive heat warnings for portions of southeast California, southern Nevada and southern Arizona from Friday morning through Sunday evening. This includes the cities of Las Vegas, Phoenix and Tucson. READ MORE