More than 50 million are under heat alerts from the West Coast to the Southeast.

It's the first day of July and dangerous heat is already building in across the West Coast, central and southern Plains, and across the Southeast. The upper-level pattern shows two ridges building, including one off the West Coast and another over the lower Mississippi Valley. These ridges will help send temperatures climbing well above average and even into record territory.

The central U.S. will see highs reaching the 90s and 100s today and in the coming days. Cities such as Dallas, Wichita, Kan., and Oklahoma City will see highs near or above 100 degrees. With lows staying in the 70s and 80s, it will be difficult to cool down. In the Southeast and along the Gulf Coast, humidity will send "feels like" temperatures into the triple digits. There will be little relief from the heat this week in these regions.

Extreme heat will also begin building along the West Coast tomorrow. While the immediate coast will stay cooler, interior communities in California will range from 100 to 110 degrees. New record highs are possible across the San Joaquin and Sacramento valleys on Tuesday and Wednesday. This heat will continue into the Fourth of July holiday on Thursday and through the remainder of the week.

With dangerous heat in the forecast, it's important to stay hydrated, wear loose and light colored clothing and check conditions on the TemperatureRadar before heading outdoors.