Arecord-breaking "scorcher" heatwaveis underway in Southern California on March 17 and dangerous heat reaching up to triple digits will spread across much of the Southwest, forecasters said.
The heat is expected to stretch into the weekend and is likely to challenge or shatter several daily records, and potentially records for the entire month of March, according to the National Weather Service.
More than 18 million people were under extreme heat warnings the morning of March 17 across Southern California, southern Nevada and parts of Arizona. Millions more were under heat advisories in the region. The weather service office in Los Angeles warned of "dangerously hot" temperatures.
"There is a HIGH risk for heat illness this week, with conditions remaining warm overnight adding to the heat risk," the weather service said.
What makes this heatwave so unusual and dangerous, forecasters say, is not just the level of heat, but also the timing. Some major cities will see temperatures in the high 90s and triple digits weeks or months before they normally would.
More:Record-breaking temps, wind and rain follow bizarre weather across US
"The impacts of this heat will extend beyond daily temperature records, with faster snowmelt,drying vegetationand growing stress on water resources across parts of the West," said Elizabeth Danco, AccuWeather meteorologist.
Here's what we know about the heatwave in the Southwest:
A deep freeze across the South, a spreading heat wave in the West and a trail of high winds and downpours leaving the East are in the forecast on March 17 after a weekend of bizarre weather across the country.On the heels of a major storm that delivered downpours, high winds and thunderstorms along the U.S. East Coast, the National Weather Service is predicting a "quieter" period of weather for many. See the storm's toll in photos.
Work crews clear downed trees on Holtville Road north of Wetumpka, Ala., after early morning storms on Monday March 16, 2026.
Severe weather slams parts of the US. See the toll in photos
A deep freeze across the South, a spreading heat wave in the West and a trail of high winds and downpours leaving the East are in the forecast on March 17 after a weekend of bizarre weather across the country.
On the heels of amajor storm that delivered downpours, high winds and thunderstormsalong the U.S. East Coast, the National Weather Service is predicting a "quieter" period of weather for many. See the storm's toll in photos.Work crews clear downed trees on Holtville Road north of Wetumpka, Ala., after early morning storms on Monday March 16, 2026.
How long will the heatwave last?
The "unusually early" heatwave is expected March 17 in Southern California, where high temperatures could get close to 100 degrees, the weather service said.
In Los Angeles, heat warnings and advisories are in place through March 20. According to forecasters there, temperatures this week are expected to be 15 to 30 degrees above average for this time of year, breaking many daily records and even possibly a monthly record in the majority of areas. Heat in Los Angeles will peak March 17 through March 19, with highs between 90 and 103 degrees across coastal plains, valleys and the interior region. Coastal areas could get as warm as 80 to 90 degrees.
Next week will cool down some, forecasters in Los Angeles said, but temperatures will still be 10 to 15 degrees above normal.
More:How to stay cool during extreme heat
By the afternoon of March 18, temperatures will soar over 100 degrees across much of the Desert Southwest, the weather service said.
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According to AccuWeather the heat dome will expand across several states, impacting as many as 70 million people through the weekend and possibly into early next week.
These major cities could break heat records
Several areas in Southwestern states could break daily heat records, or even March records. Record highs are possible from California to the Rockies, including cities like Salt Lake City, Albuquerque and Denver, AccuWeather reported.
"Temperatures this hot so early in the year could shatter high temperatures records by as much as 10 degrees," the weather service said.
Los Angeles could potentially break its March record of 99 degrees, and if the heatwave lasts five days, it will be the longest for the area ever recorded this early (the current record is a four-day heatwave in March 2015), AccuWeather reported. Downtown Los Angeles could break these daily heat records, according to the weather service there:
March 17: 94 in 1914
March 18: 87 in 1997
March 19: 97 in 1997
March 20: 93 in 1997
Phoenix could reach up to 106 degrees from March 19 to March 21, about 20 to 30 degrees above historical average, AccuWeather reported. In Phoenix, the earliest recorded date to reach 100 degrees was March 26, 1988, but on average the city doesn't reach 100 degrees until May.
Here are therecords at stake in Phoenix, according to the weather service office there:
March 17: 99 degrees
March 18: 95 degrees
March 19: 96 degrees
March 20: 97 degrees
Las Vegas could also hit 100 degrees this week, weeks ahead of its usual timing for triple digits. If it gets over 93 degrees, Las Vegas will break its March record last set in 2022.
The Coachella Valley in California, which includes Palm Springs, could reach up to 105 or 110 degrees this week, the weather service said.
Even the Northern California is seeing record heat. On March 16, Redwood City broke its March record for high temperatures, the weather service in San Francisco said. San Francisco could have highs in the lower 80s, passing daily records that have existed for decades, AccuWeather reported.
Heatwave could drive earlier fire season
The heat wave in Southern California comes after the region has seen average temperaturesup to 8 degrees above normalthroughout December 2025 and January.
The heat, combined with recent Santa Ana winds, is going to speed up the process that dries out green vegetation, called "curing," which usually doesn't happen until May or June, according to AccuWeather lead long-range expert Paul Pastelok.
That could mean wildfires could ramp up earlier in the year, with dry vegetation acting as fuel. Cal Fire Battalion Chief Brent Pascua said vegetation still has some moisture, but authorities are keeping a close eye on conditions and a current lack of rainfall.Read more here.
Contributing: Paris Barraza
This article originally appeared on USA TODAY:Dangerous 'scorcher' threatens heat records in California, Southwest