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Southwest heat wave intensifies, breaks records and worsens drought

Andrew Freedman

Axios | 2021-06-16T14:57:52.057878Z

A temperature "misery index" shows peak levels across the Southwest (orange and yellow), and the upper air flow shows how the jet stream is being pushed north, away from the heat dome hovering to impact the Four Corners region. (Earth.nullschool.net)

 

A punishing and long-enduring heat wave is intensifying in parts of the West and Southwest, with heat warnings and advisories in effect across seven states Wednesday. The heat will not relent until late in the weekend.

Threat level: In the coming days, 40 million are likely to see temperatures reach or exceed 100 degrees.

Why it matters: The extreme heat is unusually intense for June, and is aggravating already dire drought conditions that could lead to another devastating wildfire season.

The details: Overnight minimum temperatures in Las Vegas barely slipped below 90°F early Wednesday, and daytime highs are anticipated to approach the city’s all-time record of 117°F today through Saturday.

• In Phoenix, the low temperature Tuesday night into Wednesday warming was a stifling 91°F.
• The heat wave is the result of a sprawling area of high pressure at the surface and aloft, also known as a heat dome. It's deepening the already extreme drought across the West, and adding to the significant wildfire danger across the region.
• Wildfire risks are especially heightened from Arizona to California, northeastward into Montana. In Arizona and New Mexico, lightning from scattered thunderstorms could trigger new wildfires beginning Wednesday, as they mainly bring dry lightning and dust to a parched region.
  

The big picture: The West is currently experiencing its most intense and expansive drought of the 21st Century, and the heat wave and drought are reinforcing one another.

• One of the clearest conclusions of climate science is that heat waves are becoming more intense and longer-lasting as the climate warms overall. In some cases, climate studies have shown that extreme heat events could not have occurred in the absence of human-caused global warming.
• In recent years, there has also been a trend toward stubborn and sprawling heat domes that block storm systems and keep hot weather locked in place for days at a time.

The bottom line: The summer temperature outlook from the Weather Service shows a high likelihood of above average temperatures across the West and Southwest, in part driven by prevailing weather patterns as well as the drought conditions.