Temperatures to climb to extreme levels even for hottest part of US

More than 50 million Americans in the southwestern U.S. are under heat advisories or warnings as temperatures will take a run at records that have stood for nearly 50 years in some locations.

 More than 50 million Americans in the southwestern United States are under heat advisories or excessive heat warnings as a blistering heat dome maintains its grip on the region. The heat will place additional stress on the energy grid, elevate the threat of wildfires and increase the risk of heat-related illnesses.

Temperatures will climb to levels unusual even for the notoriously hot region of the U.S., putting long-standing records in jeopardy. A sprawling area of high pressure that is positioned over the Southwest, known as a heat dome to meteorologists, is the culprit behind the extreme temperatures.

“This [pattern] will help to keep most showers or storms at bay and allow for sunny skies that will help boost temperatures,” explained AccuWeather Meteorologist Andrew Johnson-Levine.

AccuWeather meteorologists say that the scorching conditions can intensify heading into the weekend and even expand into parts of the Central states and Southeast by next week.

 Numerous records will be challenged

Several records will likely be challenged throughout mid-July across this corner of the country, including metro areas like Phoenix. Daily highs can be at risk throughout the upcoming week in Arizona's Valley of the Sun, with the peak of the heat this week likely to occur by Thursday. In addition to daily high-temperature records being at risk, a separate, long-standing record also stands a chance of being broken.

Observations show that Phoenix has reached the 110-degree mark or higher each day since June 30. AccuWeather forecasters say the area can challenge the existing 18-day record for that temperature mark as July trudges on. The previous record was set almost 50 years ago, in 1974.

In addition to setting records, there remains an outside chance that parts of the Phoenix area can reach 120 degrees.

"While the 120-degree mark is not a certainty for Phoenix, it is possible late this week and this upcoming weekend as a high-pressure area and northward bulge of the jet stream simultaneously strengthen and force the core of the hottest air westward for a time," AccuWeather Senior Meteorologist Alex Sosnowski said.

 "Phoenix has only reached the 120-degree Fahrenheit mark three times since records have been kept dating back to 1929. The last time temperatures topped that mark was on July 28, 1995, when a high of 121 was recorded. The all-time record high of 122 was set on June 26, 1990," Sosnowski added.

As long as the dome of high pressure across the Four Corners keeps thunderstorms at bay this week, locations including Phoenix may stand a chance of climbing near or to the 120-degree mark by late week. Currently, the city is forecast to meet or exceed the existing daily max temperature record on more than one occasion later this week, and experts warn that residents are unlikely to get relief from the heat once the sun goes down.

The record for most consecutive days above 100 degrees for El Paso, Texas, was broken Sunday when the mercury topped 100 F for the 24th consecutive day. The previous record of 23 consecutive days was set back in 1994. High temperatures are forecast to remain above 100 in El Paso through at least this coming weekend.

Residents face risk of heat-related illnesses

"Aside from daytime temperatures, heat may stick around at night. Summertime temperatures in the desert usually plunge into the 70s or 80s. Later this week, some spots, including Phoenix, may be stuck near 90 overnight," said Johnson-Levine.

Elevated overnight temperatures can pose hidden health dangers, particularly to those in highly urbanized areas that face the urban heat island effect. Metropolitan areas constructed of a high density of buildings and roadways are often made up of materials that can absorb the daytime heat more easily than rural or vegetative landscapes, allowing surfaces such as concrete or asphalt to continue to release heat after the sun goes down.

During a heat wave, residents can still face elevated temperatures during the overnight hours compared to what is typically observed, which can place additional strain on the heart as the body tries to regulate the internal temperature. With overnight low temperatures this week expected to linger in the upper 80s to mid-90s F, residents are urged to take steps to stay cool at night.

Very high cooling demands are expected to persist in the Southwest this week and even into next week as fans and air conditioners are cranked into high gear.

"While the Desert Southwest cities are usually quite hot in July, this week will bring heat that is highly anomalous. In Las Vegas, daytime highs usually hover around 105 degrees in July, with Phoenix a few degrees warmer. As temperatures may surge into the 120s, this will not be typical heat for the region," said Johnson-Levine.

This week, Albuquerque, New Mexico, is forecast to climb to 100 on multiple days. After coming close to the century mark on multiple days, the city finally had its first 100-degree high of the year Sunday. Last year, the city reached the 100-degree mark roughly a month earlier, on June 10.

Meanwhile, America's hottest location will reach levels of heat that are noteworthy over the next week. In Death Valley, California, high temperatures are set to reach the 120s beginning Wednesday and may even climb close to 130 degrees over the weekend. Even overnight, the temperature may only fall into the middle or upper 90s.

When will moisture return to the Southwest?

As the heat dome lingers in place across parts of the West this week, chances for any substantial moisture across the Four Corners region will be limited. Afternoon thunderstorms will be possible at times this week, but coverage will be rather spotty across Arizona and New Mexico.

Experts warn that although the storms may be widely separated across the region, they can be mainly dry and still contain lightning. Given the dry conditions and baking heat, lightning strikes could ignite wildfires.

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