A searing heat wave is set to raise temperatures to decidedly toasty levels across a large area of the U.S. this weekend and early next week, potentially breaking records in places like Phoenix and Death Valley, and combining with sky-high humidity across the Plains.

The baking and potentially dangerous conditions come courtesy of a large, intense ridge of high pressure that are forecast to send temperatures skyrocketing and keep them elevated for much of next week.

The event is “a potentially historic heat wave,” Dan Berc, a meteorologist with the National Weather Service office in Las Vegas, said.

 

 

 

Officials across the region are urging residents to take precautions, including drinking plenty of water and avoiding being outdoors in the midday sun.

“We do a lot of work trying to get the word out,” Berc said.

The area of high pressure, which is coinciding with the longest days of the year, will keep skies clear and conditions dry throughout the Southwest, allowing temperatures to soar.

In Phoenix, the heat is expected to peak Sunday through Tuesday, with forecast temperatures of 118°F (47.8°C) on Sunday and 119°F on Monday. The record for both dates is 115°F, while the all-time high for the city is 120°F. That temperature has only been reached three times in the records, but it’s possible it could be broken during this heat wave.

In Las Vegas, the forecast high temperature for Monday is 112°F (44.4°C), which would be 1°F shy of the record high for that day, which has also been set three times, including last year. On Tuesday, the forecast is for 114°F, which would best the record high for that date of 111°F.

Las Vegas sits in a narrow valley with differing elevations, which can cause temperatures across the city to vary by a few degrees. Temperatures in the 113°-115°F range are “about as hot as it can get here at the elevation of the airport,” where the official NWS station is, Berc said.

On June 30, 2013, the city recorded its all-time high temperature of 117°F.

 

 

 

In notoriously hot Death Valley — where the highest temperature ever measured in the U.S. was 134°F on July 10, 1913 — temperatures on Monday and Tuesday are expected to climb to 122°F and 125°F, respectively. The former would be a few degrees below the record for that date, but the latter would tie it. On Wednesday, the forecast high of 125°F is set to top the current record of 124°F.

In the Plains, residents will have to contend with the added issue of humidity, primarily courtesy of moisture from the Gulf of Mexico. That humidity can make conditions much more uncomfortable, but the famous dry heat of the Southwest can actually be more dangerous, exactly because it’s felt less.

Places across parts of Oklahoma and North Texas have been seeing heat indices in the 103°-115°F range, according to the NWS office in Norman, OK. The heat index (a measure of the combined effect of temperature and humidity) is expected to stay in the 90s through next week.

“It is a bit unusual to see the heat dome of that magnitude this early in the summer, but it’s not unheard of,” Gary McManus, the Oklahoma state climatologist, said in an email.

The heat will also bleed into the Northeast early next week, though temperatures will not get nearly as hot, staying more in the upper 80s and low 90s.

While the Southwest is typically beginning to heat up at this point in the year, the extremity of this event is unusual.

 

 

 

“It’s early to get the big heat,” Bob Oravec, lead forecaster with the National Weather Service in College Park, Md., said.

This could end up being the hottest period of summer for the Southwest, because the monsoon typically kicks in in early July, bringing cloudy, more humid weather that keeps temperatures from soaring quite so high.

“There’s no way we’re hitting that 115°F temperature after the monsoon begins,” Berc said, though summer still isn’t exactly cool. A normal July in Vegas will average about 105°F and temperatures there will stay above 100°F through July and August.

This heat wave could help boost the overall U.S. average temperature this year, which is having its fourth hottest year-to-date through May. The world as a whole is blowing away last year’s record heat so far, and is poised to take the title of hottest year.

An exceptionally strong El Niño provided a push to global temperatures this year, but the excess heat trapped by greenhouse gases in the atmosphere was the primary driver.

The signs of warming in extreme heat are becoming increasingly clear. Record highs are outpacing record lows so far this year across U.S. by a ratio of six to one. That kind of trend is one of the more solidly anticipated results of global warming.

Warming has led to a rise in average summer temperatures across the U.S., with the Southwest the fastest-warming region during that season. Since 1970, summer temperatures there have risen by 3.6°F (2°C) per decade on average, compared to 0.5°F per decade for the contiguous U.S.

 

 

 

If greenhouse gas emissions aren’t curtailed, those temperatures could rise another 10°F (5.5°C) by century’s end, according to the National Climate Assessment.

To put that rise in more concrete terms, a Climate Central analysis comparing future summers in U.S. cities to those in other spots today found that summers in Phoenix by 2100 will be more like those in Kuwait City, where summer temps hit 114°F.

Beyond average temperatures, recent studies have suggested that extreme heat is likely to become more and more prevalent in the future. One such study found that heat waves that today strike only about once every 20 years could become an annual threat by 2075 for much of the world.

Another study, to be published in an upcoming special issue of the journal Climatic Change, found that by late in the century, the odds that any summer will be hotter than the hottest currently on record were 80 percent, including in parts of the U.S.

 

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