Extreme Heatwave Hits US West Coast This Week

Tue Mar 17 2026 20:51:42 GMT+0000 (Coordinated Universal Time)

An unusual early-season heatwave is sweeping across the southwestern United States, with temperatures expected to soar into the triple digits, affecting millions and raising health concerns.

A significant heatwave is forecasted to impact the southwestern U.S. this week, with temperatures in Phoenix potentially exceeding 100°F (38°C) as early as Wednesday. The heat, driven by a high-pressure system, is expected to elevate temperatures 20-30°F above seasonal norms, presenting health risks to residents, especially vulnerable populations. Concerns over reduced snowpack and the possibility of water shortages later in the year are escalating as the region braces for prolonged high temperatures.

An unusual early-season heatwave is sweeping across the southwestern United States this week, with temperatures expected to reach levels more typical of early summer rather than mid-March.

In Phoenix, Arizona, the National Weather Service (NWS) warns that temperatures could exceed 100°F (38°C) by Wednesday, marking the earliest arrival of such intense heat in nearly forty years.

A strong, slow-moving high-pressure system, often referred to as a heat dome, is trapping hot air over the region, resulting in temperatures that are substantially above average for this time of year, impacting parts of California, Nevada, and Arizona.

This oppressive heat is predicted to last for several days, with limited overnight cooling, affecting millions of residents across the southwestern states.

Highs are expected to exceed 90°F in many places, including coastal areas, while desert regions may reach even hotter conditions, challenging established mid-March records.

The NWS has issued heat advisories for parts of California, including the Bay Area and central coast, where afternoon highs could approach 90°F.

With temperatures rising, residents are being urged to take precautions, particularly with vulnerable populations such as the elderly, and to plan activities to avoid the peak heat hours.

Officials in Las Vegas have noted that Extreme early-season heat coupled with high tourism rates will make this heat very dangerous for those not acclimated to the heat, especially for travelers from cooler climates. The heatwave could extend into next week, prompting concerns about the health risks posed by the extreme temperatures.

This intensified heat poses a threat to California's snowpack, which is crucial to the state's water supply, as it accelerates melting at a critical time when snow usually builds up. This could lead to significant water shortages over the summer months, threatening the state's water supply.

Even though wildfire risk is generally lower across much of the Southwest due to light winds, conditions can be quite different further east, where dry air and persistent breezes raise the likelihood of wildfires igniting and spreading rapidly.

The arrival of this heatwave follows a period of severe weather across the Midwest and Great Lakes, with the risk of strong storms and tornadoes moving eastward. As we progress through the week and into next week, above-average temperatures are likely to expand across much of the United States.