A powerful heatwave has gripped the southwestern U.S. this weekend with roughly 53 million Americans facing excessive heat warnings. The heat is expected to move east beginning Monday, according to meteorologists.

Cities and areas that saw record temperatures included Phoenix, Las Vegas, Denver and California’s Death Valley. Texas is also experiencing excessive heat.

On Saturday, Las Vegas reached 109 degrees Fahrenheit, which broke its record for the hottest day on that date since 1956. Phoenix hit 114 degrees, which broke its record from 1918, and Denver was at 100 degrees, breaking its record from 2013, The National Weather Service reported.

Death Valley, located in southeast California near the border of Nevada, reached 122 degrees, a record for the day. Other nearby areas also reached triple digits.

Heat warnings and advisories were issued for parts of Northern California through the Central Valley and down to the southeastern deserts near Palm Springs.

Most of California’s coastal cities were able to dodge the excessive heat this weekend. San Francisco and parts of northern California experienced some severe heat early Saturday that eventually cooled off in the afternoon.

The National Weather Service warned that heat is the leading cause of weather-related deaths most years.

As the temperatures continue to rise, the NWS noted that, “You are generally safe indoors with the AC on, while staying hydrated. During extreme heat, stay inside and keep cool.”

Outside the U.S., there is a severe heatwave hitting Portugal and Spain. In Evora, Portugal, the heat is expected to reach 106 degrees Fahrenheit on Tuesday. Temperatures are expected to reach 111 degrees on Tuesday in Seville, Spain.

Parts of Spain experienced record heatwaves in May.