Southwest Heat Dome Could Threaten All-Time Records, Including Las Vegas

 Chris Dolce

Published: July 15, 2023

A dangerous heat wave in the West and parts of the South will threaten records into next week as a heat dome intensifies and remains parked over those regions. Sunday is expected to be the hottest day in years in some spots.

Heat alerts are in effect for millions of people. The National Weather Service (NWS) has issued excessive heat warnings and heat advisories for more than a dozen states in the West and South. That means outdoor activities should be limited in these areas either right now or in the coming days because of the possibility of heat-related illnesses.

H​ere's how hot it will be into early next week. Triple-digit temperatures will be a fixture from much of Texas into the Southwest and California (except near the coast and in the mountains). Parts of the Desert Southwest will easily be in the 110s, even 120s in spots.

M​orning lows won't offer much relief. Phoenix could see its low temperature only bottom out in the lower or mid-90s on multiple mornings over the coming days. Thursday's morning low only dropped to 95 degrees, which was just one degree shy of tying the warmest low temperature on record in the city's history.

(​MORE: Why Heat Waves Are A Danger At Night)

T​he dome of high pressure will expand across the nation's southern tier through the middle part of next week. That means many other parts of the South will see increasingly hot temperatures.

R​ecord-breaking temperatures expected. Numerous daily records will be threatened, but some all-time record heat is within reach.

Through Monday, daily record highs will be most numerous from inland parts of California into Arizona, Nevada, Utah, New Mexico and western Colorado. Parts of southern and central Texas will also approach daily record highs into the early portion of next week.

Here are some additional heat notables that could be approached.

-Las Vegas: The city's official all-time record of 117 degrees could be approached or tied Sunday or Monday. Unofficial records indicate the city might have been as hot as 118 degrees on July 26, 1931, according to weather historian Chris Burt.

-Phoenix: Monday could be the record-tying 18th straight day of its temperature hitting 110 degrees or hotter. They could also set a record streak in which the temperature fails to drop below 90 degrees. Once the peak of the heat eases a bit, it could end up being the city's hottest week on record, according to NOAA meteorologist Alex Lamers.

-D​eath Valley: Highs in the mid to upper 120s are likely, but there's a chance it could inch up to 130 degrees. A 130-degree temperature has only happened three other times in its official records, most recently in the summers of 2020 and 2021.

(​MORE: Why Death Valley's Heat Is So Extreme)

-Reno, Nevada; Fresno, California; and Salt Lake City: All of those cities could come within a few degrees of their all-time record highs of 108 degrees, 115 degrees and 107 degrees, respectively, Sunday into Monday.

H​ow a heat dome contributes to extreme temperatures. A strong area of high pressure in the upper atmosphere is the main culprit in this heat wave. The high causes air to sink toward the ground, which compresses the air and makes it even warmer.

T​he heat dome in this case is also delaying the Southwest monsoon from really getting going by blocking most moisture from pushing into the region from Mexico or the nearby eastern Pacific waters. When monsoonal moisture is present in the air it can keep extreme heat at bay, though makes it feel more humid and uncomfortable.

Here's how to stay safe. The hot conditions will be particularly dangerous for vulnerable groups, such as the sick and the elderly. The NWS has useful heat safety tips that can be incorporated into a daily routine when extreme heat sets in.

-Job sites: Stay hydrated and take breaks inside as often as possible. Remember that in temperatures above 110 degrees, you will not know that you are sweating.

-Indoors: Check up on the elderly, sick and those without air conditioning.

-In vehicles: Never leave children or pets unattended – look before you lock.

-Outdoors: Limit strenuous activities and find shade. Drink plenty of water and avoid alcohol.

(MORE: 4 Things Extreme Heat Can Do To Your Body)

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.