Over 110 million people across 21 states are under heat warnings and watches for the July 4th holiday period. The West is bracing for dangerous and potentially historic extreme heat in the coming days, with temperatures possibly reaching 115 degrees.

The National Weather Service (NWS) office in San Francisco warned that this heat event could last 6 to 12 days, marking the longest stretch of extreme temperatures the Bay Area has seen in at least 18 years. Several daily heat records were broken on Tuesday, and more than 130 could be set through next Tuesday.

"Record-breaking and dangerous heat is forecast to make this Fourth of July week a scorcher across much of the West and from the southern Plains to the Mid-Atlantic," the NWS said.

The office added that heat is the number one weather-related cause of death in the U.S., and it is very likely that we will add to that statistic if preparations are not taken seriously.

Excessive heat warnings are in place for much of California, southern Nevada, and parts of Arizona, Washington, and Oregon. These warnings indicate potentially life-threatening conditions, with a high to very high risk for much of the population due to long-duration heat with little to no overnight relief.

The extreme heat also increases the risk of wildfires. Some four million people, mostly in California, are under Red Flag warnings, which urge people to be careful with open flames — an added risk with holiday firework displays taking place.

In addition to the heat, there is also the chance for stormy weather across the central U.S. to disrupt some holiday gatherings. Some 13 million people are under risk of severe storms across the western High Plains and the Ohio River Valley. High wind is likely across both areas, along with hail and isolated tornadoes for the region.