Deadly hot weather peaks in California on Friday as the stifling heat marches east through the weekend

By Allison Chinchar, CNN Meteorologist

Over 35 million people are under heat advisories or excessive heat warnings from California to Texas, as the high temperatures peak in the West and spreads eastward over the weekend.

The alerts cover portions of more than half a dozen states as the mercury climbs over the 100 degree mark in many locations.

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From Sacramento to Houston, records are possible Friday. In fact, more than 75 cities across the US could break daily records over the next few days, and even overnight low temperatures are expected to reach dangerous levels.

The record heat spreads east this weekend

The desert is a hot place, but this is extreme levels even for the Southwest.

Las Vegas will approach 110 degrees Friday, which is more than 10 degrees above normal.

On Saturday, Phoenix could top 115, which would break the daily record of 114 set in 1918.

Over 223 million people, about 70% of the Lower 48, will see temperatures of 90 or above over the next week.

Of those 223 million, 45 million, or about 15%, will see temperatures in the triple digits over the next week, mostly across California’s Central Valley, the desert Southwest, and Texas.

Across most of California, Friday will definitely be the peak day for heat, with San Jose forecast to reach 95, while Bakersfield and Sacramento are expected to hit over 100 degrees.

As the heat retreats from California, it begins to ramp up farther east this weekend. By the time Sunday rolls around, most of the record temperatures are expected between Phoenix and New Orleans.

Already this week, both Austin and Houston set records Thursday, but both cities have the potential to break daily temperature records as many as five days in a row before this heat wave finally subsides.

That heat continues to spread into the Midwest and Southeast through early next week, with Chicago topping out in the 90s on Tuesday and Wednesday.

On Monday, most of the record temperatures will stretch between Denver and Raleigh, North Carolina, but could spread as far north as Wisconsin and Michigan by the middle of the week.

Nighttime temperatures can be dangerous, too

While daytime highs are expected to reach record levels in some states, the overnight low temperatures are equally as important.

On Friday morning, Phoenix recorded a low temperature — yes, a LOW temperature — of 88. This is a problem because it doesn’t allow the body to successfully cool down at night.

“Your body requires cooling off at night, and actually expects it while you’re sleeping,” says Jenn Varian, meteorologist at the National Weather Service Las Vegas office. “When we have very warm overnight temperatures, your body is simply not able to cool off properly, which in (and) of itself can cause complications, but will set you up to be less prepared for the daytime heat as well.”

The temperature needs to drop to at least 80 degrees for recovery to begin. In fact, a person can lose up to 2 liters of fluid overnight through sweating if the temperature never drops below 85 degrees.

More than half a dozen states will have morning low temperatures between 10-15 degrees above normal through Sunday.

Heat is the No. 1 cause of weather-related deaths in the US, and providing guidance about the likelihood of heat-related ailments — including cramps, exhaustion, stroke and possibly death — helps protect the public in extreme heat.

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