Record-Setting March Heatwave Affects U.S. Southwest and Extends Eastward

Southwest and Midwest Grapple with Unprecedented March Heatwave

An unusual and prolonged heatwave impacted the U.S. Southwest and parts of the Midwest and Southeast throughout March, leading to the establishment of new temperature records. Temperatures significantly surpassed typical March averages, prompting public safety concerns, wildfire warnings, and discussions about the influence of climate change. The heat event, which largely peaked from Tuesday through Friday of the last week of March, led to a new U.S. all-time March temperature record.

Record Temperatures Across Regions

The heatwave resulted in numerous daily, monthly, and an all-time U.S. March temperature record.

A new United States record for the highest March temperature was set at 110 degrees Fahrenheit (43.3 degrees Celsius) near Martinez Lake, Arizona, on March 28.

United States Record:

• A temperature of 110 degrees Fahrenheit (43.3 degrees Celsius) was recorded near Martinez Lake, Arizona, on March 28, establishing a new United States record for the highest March temperature. This surpassed the previous record of 108 degrees Fahrenheit (42.2 degrees Celsius) set in Rio Grande City, Texas, in 1954, which was equaled by North Shore, California, on March 27. Cathedral City and Thermal, California, also reached 108 degrees Fahrenheit on March 28.

Southwest Region:

• Arizona: Phoenix experienced its earliest triple-digit temperature on record, reaching 101 degrees Fahrenheit on March 27. The city subsequently recorded 105 degrees Fahrenheit on March 28. Historically, the earliest triple-digit day in Phoenix was March 26, 1988. Projected temperatures in Tucson reached 98 degrees Fahrenheit.
• California:
  • Southern California's temperatures were 20 to 30 degrees Fahrenheit above normal for March, with coastal areas reaching the 80s and 90s, and inland regions exceeding 90s and reaching 100 degrees Fahrenheit or higher. Normal March temperatures for the region are typically in the high 60s or 70s.
  • Palm Springs reached 104 degrees Fahrenheit on March 27, tying its 1966 record for the hottest March day. It then recorded 105 degrees Fahrenheit on March 27 and 107 degrees Fahrenheit on March 28, surpassing its all-time March record.
  • Hollywood Burbank Airport recorded 92 degrees Fahrenheit on March 25, exceeding its 2004 daily record of 91 degrees Fahrenheit.
  • Pierce College in Woodland Hills reached 97 degrees Fahrenheit on March 25, surpassing its 2007 daily record of 94 degrees Fahrenheit. Woodland Hills later recorded 102 degrees Fahrenheit on March 28.
  • Downtown Los Angeles reached 94 degrees Fahrenheit on March 27, exceeding its 1997 daily high of 87 degrees Fahrenheit.
  • Lancaster recorded 93 degrees Fahrenheit on March 28, surpassing its 2004 record of 87 degrees Fahrenheit. Riverside reached 101 degrees Fahrenheit on March 28. Anaheim reached 95 degrees Fahrenheit on March 27.
  • Daily records were also observed in Sacramento (88 degrees Fahrenheit), San Francisco (85 degrees Fahrenheit), San Diego (85 degrees Fahrenheit) on March 27, and at locations including Long Beach Airport, UCLA, Camarillo, Oxnard, Santa Maria, and Paso Robles on March 28.
• Nevada: Las Vegas reached 99 degrees Fahrenheit on March 27, surpassing its 2022 record of 93 degrees Fahrenheit. It set a new March record of 95 degrees Fahrenheit on March 28.
• Other Western States: Boise, Idaho, reached 80 degrees Fahrenheit on March 27, marking its earliest date for such a temperature since records began in 1875.

Midwest and Southeast:

• Portions of Nebraska experienced temperatures above 90 degrees Fahrenheit.
• In the Southeast, Savannah, Georgia (89 degrees Fahrenheit), and Columbia, South Carolina (88 degrees Fahrenheit), broke or tied daily record highs on March 27.
• Between March 1 and March 26, over 1,100 daily records and more than 100 monthly records were broken or tied nationwide.

Public Safety and Health Implications

The early arrival of elevated temperatures raised public safety concerns due to communities not being acclimated to such heat. Extreme heat is identified as a leading cause of weather-related fatalities in the United States, contributing to over 21,500 American deaths since 1999.

Vulnerable populations identified include unhoused individuals, outdoor workers, older adults, infants, children, pregnant people, and those with chronic health conditions or disabilities.

Overnight temperatures remained elevated, with lows in some areas near or exceeding average March highs, preventing adequate body cooling and increasing the risk of heat-related illnesses such as heat exhaustion and heatstroke. Hiking activities were impacted in Arizona due to high temperatures, lack of shade, and drying water sources, leading to early returns from trails. Hiking trails around Phoenix were closed due to heat illness risks. Some California and Tahoe-area ski resorts ceased or reduced operations due to rapid snowmelt and high temperatures.

Wildfire Risks

The heatwave coincided with conditions conducive to wildfires in several regions.

• Red Flag warnings were issued by the National Weather Service for over 47 million Americans across the Great Plains to the Southeast due to widespread critical fire weather danger.
• Wind gusts in the Plains were projected to reach 30 to 60 mph, and combined with low humidity and dry fuels, these conditions were conducive to rapid wildfire growth.
• Gusty winds and dry conditions were also anticipated along the Gulf Coast and inland across the Southeast.
• Increased wildfire risks were noted in Colorado due to the combination of extreme heat, gusty winds, and low humidity.
• Evacuation orders were lifted for areas impacted by Nebraska’s Cottonwood and Morrill fires, which had burned over 1,200 square miles (3,118 square kilometers) and were largely contained.

Attribution and Climate Context

International groups of scientists, including World Weather Attribution, concluded that the March heatwave would have been "virtually impossible" without human-caused climate change.

Their analysis indicated that the climate crisis, primarily caused by the burning of fossil fuels, has quadrupled the likelihood of such a heatwave occurring over the past decade. Researchers noted that the observed temperatures were "completely off the scale for March."

Globally, 2024 was recorded as the warmest year by the National Oceanic and Atmospheric Administration, with the U.S. experiencing 10 of its warmest years since 2012. The persistence of high pressure, referred to as a "heat dome," was identified as a contributing factor to trapping hot air across the region.

Official Responses and Recommendations

Authorities issued various warnings and recommendations to address the heatwave.

• Extreme heat warnings and heat advisories were in effect across large portions of California, Arizona, and Nevada.
• California state officials, who launched an action plan in 2022 to address heat-related deaths, focused on public education, protecting outdoor workers, and supporting urban green spaces, tree planting, and cooling centers.
• Cooling centers were made available at public libraries and community centers in areas like Los Angeles County.

The weather service advised residents to hydrate, avoid outdoor activity or work between 10 a.m. and 5 p.m., and check on vulnerable neighbors and loved ones.

• Evaluation of cooling center hours was suggested, particularly regarding their nighttime availability given the warm overnight temperatures.

Future Outlook

Temperatures in Southern California were projected to decrease during the weekend following the peak heat, with further cooling anticipated, then a slight increase into the following week.

• A cooldown moved across the Midwest and Northeast after unseasonably warm days, with temperatures expected to be 10 to 20 degrees Fahrenheit lower than previous highs before rebounding to seasonable levels.
• Record-setting heat was projected to persist in the Southeast throughout the weekend.
• Long-term forecasts from the National Weather Service indicated that April, May, and June are likely to be warmer than average across most of the U.S., with the exception of the Northeast and Great Lakes regions. Arizona, Nevada, Utah, and New Mexico were predicted to experience an even hotter spring than typical.