Extreme March heat wave will scorch Los Angeles and the Southwest this week. The long-term consequences could devastating

An “unprecedented,” potentially record-breaking heat wave is expected to hit much of the American southwest, from California to Colorado, this week—and experts are concerned about how temperatures will affect the region’s already-low snowpacks.

Temperatures in the Los Angeles area will be 15 to 25 degrees above seasonal norms on Thursday, March 12, and Friday, March 13, according to the National Weather Service (NWS), reaching into the 90s along the coast and potentially above 100 degrees in some areas. 

“Given the unprecedented length and magnitude of this extreme heat wave, heat stress will be increasing each day, especially in areas that aren’t used to the heat, like the coastal areas,” forecasters wrote. 

Scorching temperatures will stretch through the southwest

Tucson, Arizona, could see its earliest 100-plus degree day next week; the March monthly record high for Tucson is 99 degrees, according to the NWS. Parts of Colorado are forecast to reach into the 90s, which would break state records.

Some parts of the southwest could see triple-digit temperatures, when they have never before experienced that this early in the year, climate scientist Daniel Swain said on a recent livestream.

The heat wave is expected to last for the “foreseeable future,” he added, with a 10- to 14-day stretch of “extraordinarily anomalous weather.” 

“It is quite likely that many cities and probably many states will set new all-time high March temperature records, as well as new records for the month of March cumulatively overall,” Swain said. “All the way from Colorado to California, I think we’re going to hit records everywhere in between.”

Heat wave threatens already-low snowpacks

The extreme March heat wave comes on the heels of the warmest winter on record for the majority of the American west and Southern Plains. That’s based on 131 years of climate data.

It was also an exceptionally dry winter across the West, which has left the region, including the Sierra Nevada, with below-average snowpacks. 

Many Western communities, including in California, depend on snowpacks as crucial natural reservoirs. They store water through the winter and release it over the spring and summer. 

The heat waves, though, threaten to melt the already-sparse snow, which means the reservoirs may not have enough water for residents and farms later in the year. 

“The current snowpack is under 50% of its average throughout much of the American West,” Swain said. “Every single basin, with no exceptions in the Western U.S. . . . is below average.”

No “miracle March” this year

Meteorologists and climate experts use the term “miracle March” to describe the way the month can restock reservoirs, even after a winter without much water or snow. Cold, wet March conditions can “turn a dry winter into a not-so-dry winter,” Swain said.

But this year, Swain noted, “that is not going to happen.”

The record-breaking heat wave brings long-term concerns. Along with reducing the amount of water in reservoirs, it could set up dry soil conditions for the summer, which increases the risk of wildfires. 

The fact that these temperatures are coming so early in the year is also a concern for climate experts. 

“We’re about to experience the hottest March temperatures we’ve ever seen across a lot of the Western U.S.,” Swain said. “This is going to be a heat wave that people aren’t going to be able to ignore because of when it’s happening.”

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