Millions of Americans under heat warnings; Phoenix, Las Vegas could shatter records: Heat updates

Millions of Americans were under heat warnings and watches across the West and the South on Friday with multiple cities expected to shatter heat records, and it's only going to get worse and more dangerous over the weekend, officials say.

This weekend, "a searing heat wave is set to engulf much of the West Coast, the Great Basin, and the Southwest," the National Weather Service said. Much of the south-central and western U.S. has been hit by an unrelenting wave of near record-breaking temperatures in recent days and weeks, which forecasters say is intensifying.

More than 34 million people were under excessive heat warnings, and 61 million under heat advisories from the weather service as they woke on Friday morning. Nearly 730,000 Americans also were under excessive heat watches.

Between Saturday and Sunday, there are 45 record-high temperatures forecast in California, Nevada, Arizona, Texas, Florida, Oregon and Idaho, the National Weather Service said.

In Death Valley, California, which has recorded the hottest temperatures anywhere in the world, temperatures are poised to hit 130 degrees, while the weather service said daytime highs from the Great Valley region of California to the Desert Southwest will hit between 105 and 115 degrees Saturday.

Scientists say the recent record-breaking heat is evidence of climate change stoked by fossil fuel emissions.

"We're expecting a large dome of high pressure to build overhead," Accuweather meteorologist Mike Youman told USA TODAY.

Youman said Las Vegas; Fresno, California and Flagstaff, Arizona, are among the areas forecasted to approach or hit record highs.

'Oppressively hot': Southwest sees triple digits

Parts of the desert in Southern California, Nevada and Arizona will likely top 120 degrees Saturday, the weather service said.

Phoenix hit 110 degrees for the fourth consecutive day Thursday. It reached 114 degrees at Phoenix Sky Harbor International Airport, tying a record set for the day in 2020. The city's record for consecutive temperatures of 110 degrees or above is 18 days, set in 1974.

Las Vegas is set to break its hottest temperature ever recorded on Sunday, when it's forecasted to reach 118 degrees, which would break the previous record of 117.

There's a chance Death Valley will climb above 130 degrees this weekend. Its all-time heat record of 134 degrees was set in July 1913. Temperatures there will "struggle to fall below 100" overnight this weekend through Tuesday, the weather service forecasted.

Farther east, the weather service warned of "oppressively hot and steamy conditions" stretching from Texas and the lower Mississippi Valley all the way to Florida. Little relief will be offered in the early morning hours, either, with low temperatures across the South remaining "excessively warm."

High humidity to make high temperatures more brutal in Plains, Southeast

Across the Plains, Lower Mississippi Valley and Southeast, temperatures in the upper 90s and low 100s aren't the only thing people need to worry about. With the combination of high humidity, 100 degrees could feel worse than 115 degrees, the weather service reports.

The weather services forecasts the heat wave to haunt the region through this weekend and into next week. Over at least the next six days, about 27 million people across the contiguous United States will experience an air temperature or heat index above 110.

"With the humidity continuing on the air feels heavier, feels harder to breathe. So all of that is caused by those those higher dew points and higher humidity values," Youman said.

The Northern Plains, however, should get a reprieve from the heat as cooler air from central Canada dips into the region by early Saturday, according to the weather service forecast.

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What is causing the heat wave?

The National Weather Service said the soaring temperatures are due to an "upper level ridge of high pressure" over the Southwest, which is set to strengthen. A heat dome happens when a persistent region of high pressure traps the heat over an area.

Another factor impacting the heat? A shift in position of the jet stream, AccuWeather reported. Jet streams are narrow bands of strong winds high in the atmosphere sometimes called "rivers of air," according to the National Oceanic and Atmospheric Administration.

According to AccuWeather meteorologists, a northward bulge of the jet stream will be "extreme as it can be over the interior Southwest" into early next week, causing dangerously high temperatures in that region.

How to stay safe in soaring temps

Officials warn that exposure to the extreme heat can be dangerous and even deadly. Most years, heat leads all other weather-related causes of death, according to the National Weather Service. There are an average of 702 heat-related deaths each year in the country and tens of thousands of emergency room visits for heat, the Centers for Disease Control and Prevention says.

The weather service in Sacramento, California, advised residents to consider cancelling outdoor activities during the hottest parts of the day and to make sure to stay hydrated. Saturday and Sunday are being considered a "major heat risk," which means the heat is dangerous to anyone without adequate access to cooling or hydration.

If you experience confusion, dizziness, or loss of consciousness, you should call 911, the weather service said.

US heat index forecast

More severe rainfall unfolds in Midwest, mid-Mississippi Valley and returns to New England

Southern New England and the coastal Mid-Atlantic states can expect heavy rain Friday as a slow-moving cold front shifts southeastward bringing with it a slight risk of excessive rainfall, meteorologists said.

Following the catastrophic flooding earlier this week, interior New England is still sensitive to more harsh rainfall requiring the forecast "to be monitored very closely as any changes can bring big impacts," according to the weather service.

Further south, a slight risk of excessive rainfall was also in effect for the lower Mississippi Valley through the central Gulf Coast region on Friday, where severe storms could get organized through the day.

US weather watches and warnings

National weather radar

This article originally appeared on USA TODAY: Heat wave intensifies with Phoenix, Las Vegas poised to break records