More than 50 million people in the U.S. are under excessive heat warnings

More than 25 major cities tied or broke record-high temperatures Saturday, during a dangerous heat wave that enveloped much of the Southwestern United States over the weekend. Approximately 53 million people are still under excessive heat warnings as extreme temperatures begin to shift east.

California's Death Valley, which holds the world record for hottest recorded temperature (134 degrees) set over a century ago, was the hottest place in the country Saturday at 122 degrees. Palm Springs and Phoenix, Ariz., tied for second place Saturday at 114, both cities matching previous record high temps.

Robert Oravec, a lead forecaster with the National Weather Service, said the heat will move away from the Southwest beginning Monday, traveling east towards the Mississippi River Valley over the coming days.

'It'll stretch eventually by mid-week from the Great Lakes to the Southern Plains eastward. Not too hot in the northeast yet, more of an average," Oravec said. "It's a very typical heat wave pattern set up in the Southwest and spreading now into the plains. You're almost into mid-June now, so it's not uncommon to see weather patterns that support a heat wave."

Sunday's temperatures are expected to tie or break records for at least 37 monitoring stations in Colorado, New Mexico, Texas, Arizona, Oklahoma and Louisiana, according to forecasts. The high in Phoenix is expected to reach 113 degrees.

And come Monday, temperatures in Southwestern Nebraska are expected to top out at 109 degrees, according to NWS predictions. The extreme heat will continue east, where it has the potential to reach record highs, but isn't forecasted to extend beyond the Appalachian Mountain Range, Oravec said.

Excessive heat warnings and advisories were issued across the Southwestern United States Friday, stretching from southern Texas to California. According to the NWS, residents experiencing excessive heat warnings can expect temperatures 10-20 degrees above normal.

Additionally, areas where those warnings have been issued will see little reprieve at night, with temperatures staying above 75 degrees overnight. These conditions pose a serious threat for heat-related illnesses, the NWS warns.

Parts of the region, from Palm Springs in southern California to Las Vegas, Nev. and Phoenix, Ariz., saw highs up to 114 degrees Saturday. Temperatures in most areas aren't expected to drop below 80 until Tuesday, according to NWS predictions.

Extreme heat can be dangerous for anyone, but vulnerable groups including young children, elderly adults and individuals with underlying health conditions should take additional precautions. Be sure to slow down, the NWS advises, and undertake strenuous activities during the coolest parts of the day. Avoid any unnecessary exposure to the sun and heat, and always be sure to drink plenty of water to stay hydrated.

If you don't have access to air conditioning at home, consider spending time in public places that do, such as malls, libraries, movie theaters and more. Also, you can take a cold shower or bath to cool off.

If it is warmer than 90 degrees in your home, blowing warm air with a portable fan your way will actually dehydrate you faster, the NWS warns. Instead, use that fan to expel hot air from whatever room you're seeking refuge in.

And if you're running errands with young children or pets, under no circumstances should they be left in the car, according to the NWS.

According to the National Highway Traffic Safety Administration, the internal temperature of a car can climb 20 degrees in just 10 minutes. A child's body temperature rises three to five times quicker than an adults; 23 children died from vehicular heatstroke last year.

Much of the West and southwestern United States are already experiencing severe to exceptional drought conditions, according to the U.S. Drought Monitor. As a result, this weekend's heat wave comes hand in hand with an increased danger for wildfires.

The NWS has issued fire weather watches – an alert that conditions are ideal, but not imminent, for wildfires – in parts of New Mexico, Colorado, Nevada, Utah and Arizona. Though these advisories aren't an indication that a fire will occur, they should serve as a warning for residents to be prepared as wildfires become probable.