A heat wave is shattering records across the Southwest United States, with many areas experiencing temperatures 20 to 30 degrees above normal. Simultaneously, a Climate Central analysis reveals that 97% of major U.S. cities have seen hotter summers since 1970, with human-caused climate change as the dominant driver in 91% of them. The data highlight a dramatic rise in extreme heat days and regional warming hotspots, especially in the West.
A persistent heat wave is gripping the Southwest United States, with excessive heat warnings and watches in effect across Arizona , New Mexico , and parts of California through the week.
The National Weather Service has issued alerts for numerous regions, including the Little Colorado River Valley across multiple counties, the White Mountains, Eastern and Western Mogollon Rim, and the Chuska Mountains and Defiance Plateau. These alerts span from Thursday through Friday, with temperatures expected to soar 20 to 30 degrees above normal.
Meteorologist Maria Quiben from FOX 11 Los Angeles attributes the pattern to a large dome of high pressure anchored over the region, driving an offshore flow that traps warm air. In some Southern California and Arizona communities, record-breaking heat not only shattered daily highs but also set new marks for the warmest March day ever recorded. A new analysis from Climate Central underscores the long-term trend behind such extremes.
The study found that 97% of 243 major U.S. cities have experienced hotter summers since 1970, with average summer temperatures rising 2.6°F nationwide. The most dramatic warming is concentrated in the western and southern United States, led by Reno at 11.3°F warmer. Human-caused climate change is identified as the primary driver of summer warming in 91% of the cities examined.
The organization assessed average summer (June-July-August) temperatures from 1970 to 2025 and quantified the contribution of anthropogenic climate change to each city's trend. The data reveal that nearly every city analyzed (96%) now endures more hotter-than-normal summer days compared to the early 1970s-an average increase of 22 additional extreme heat days. Regionally, the Northwest has warmed by 3.8°F, the Southwest by 3.7°F, and the South by 3.0°F during summer months.
The top five locations for summer temperature increase are Reno, Nevada (11.3°F); Boise, Idaho (6.3°F); El Paso, Texas (6.3°F); Las Vegas (6.2°F); and Salt Lake City, Utah (6.0°F). Meanwhile, the cities with the largest gains in extremely hot summer days are Reno (68 more days); Houston (58 more days); Albany, Georgia (55 more days); and Las Cruces, New Mexico and New Orleans, Louisiana (both 53 more days).
In 221 cities, or 91% of the sample, human-caused climate change accounted for at least half of the observed warming. This warming stems from heat-trapping carbon pollution produced by burning fossil fuels for transportation, electricity, heating and cooling. Hotter summers raise the risk of frequent and intense extreme heat events, which pose serious health hazards. They also fuel greater wildfire danger, drive up air conditioning energy costs, and intensify urban heat island effects
Heat Wave Southwest US Climate Central Summer Warming Extreme Heat Human-Caused Climate Change Temperature Records Arizona New Mexico Reno Las Vegas
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