A significant and unusually early heatwave is building across the south-western US this week, bringing temperatures more typical of early summer than mid-March. In Phoenix, Arizona, the National Weather Service (NWS) forecasts temperatures could exceed 100F (38C) as soon as Wednesday, the earliest arrival of triple-digit heat to the city in nearly four decades. A strong, slow-moving high-pressure system - often called a heat dome - is trapping hot air over the region, pushing temperatures 20–30F above normal in parts of California, Nevada, and Arizona.
The heat is expected to persist for several days, with limited overnight cooling adding to the strain. Millions are likely to be affected, with highs expected to reach well above 90F in many areas, including typically cooler coastal regions. Inland and desert locations could exceed 100F, with some spots approaching or surpassing 110F, challenging long-standing March records. NWS has issued heat advisories for parts of California, including the Bay Area and central coast, where temperatures could reach around 90F.
Residents are being warned to check on the elderly and other at-risk groups as temperatures climb, and to schedule events around peak heat. According to the Las Vegas NWS office, Extreme early-season heat coupled with high tourism rates will make this heat very dangerous, particularly for those not acclimated to the heat and/or traveling from cooler climates.
The heatwave could result in a prolonged period of unseasonably high temperatures, raising health risks and environmental concerns. In California, this heatwave threatens an already below-average snowpack by accelerating melt earlier than expected. With temperatures above normal, the Sierra Nevada is likely to lose snow weeks earlier than usual, compounding potential water shortages in the summer months.
Despite the current heatwave, wildfire risks remain low in the Southwest due to lighter winds limiting the spread of fire. In contrast, conditions further east near the Rockies could create a more favorable environment for wildfires. As this heatwave develops, residents across the U.S. should prepare for above-average temperatures that may shift from regional to widespread by the end of the week.
The heat is expected to persist for several days, with limited overnight cooling adding to the strain. Millions are likely to be affected, with highs expected to reach well above 90F in many areas, including typically cooler coastal regions. Inland and desert locations could exceed 100F, with some spots approaching or surpassing 110F, challenging long-standing March records. NWS has issued heat advisories for parts of California, including the Bay Area and central coast, where temperatures could reach around 90F.
Residents are being warned to check on the elderly and other at-risk groups as temperatures climb, and to schedule events around peak heat. According to the Las Vegas NWS office, Extreme early-season heat coupled with high tourism rates will make this heat very dangerous, particularly for those not acclimated to the heat and/or traveling from cooler climates.
The heatwave could result in a prolonged period of unseasonably high temperatures, raising health risks and environmental concerns. In California, this heatwave threatens an already below-average snowpack by accelerating melt earlier than expected. With temperatures above normal, the Sierra Nevada is likely to lose snow weeks earlier than usual, compounding potential water shortages in the summer months.
Despite the current heatwave, wildfire risks remain low in the Southwest due to lighter winds limiting the spread of fire. In contrast, conditions further east near the Rockies could create a more favorable environment for wildfires. As this heatwave develops, residents across the U.S. should prepare for above-average temperatures that may shift from regional to widespread by the end of the week.
