Historic Heat Wave Shatters Records Across the Western U.S.

An unprecedented March heat wave is gripping the Western United States, breaking temperature records across multiple states and raising concerns about an early start to wildfire season. The unusual warmth extends from California to the Great Plains, with temperatures exceeding averages by 10 to 15 degrees Celsius (18 to 27 degrees Fahrenheit).

Record-Breaking Temperatures

As of March 19, 2026, numerous cities have already tied or broken March temperature records. Redwood City, California, reached 90 degrees Fahrenheit on both March 17th and 18th, a first for the month in 96 years . Santa Ana, California, hit 100 degrees Fahrenheit on March 18th, and Flagstaff, Arizona, tied its March record of 73 degrees Fahrenheit . Phoenix, Arizona, recorded its hottest March day ever, reaching 39 degrees Celsius (102 degrees Fahrenheit), surpassing a previous record set in 1988 .

Scope of the Heat Wave

The heat wave isn’t limited to specific areas; it stretches across a vast region. Temperatures in Southern California, southern Nevada, and parts of Arizona are reaching dangerous levels, with over 18 million people under extreme heat warnings and millions more under heat advisories . Even inland areas are experiencing unseasonably high temperatures, such as Fort Collins, Colorado, which reached 29 degrees Celsius (84 degrees Fahrenheit), typical for late June . San Francisco is experiencing its hottest start to spring in nearly 20 years, with temperatures nearing 90 degrees Fahrenheit .

Contributing Factors and Concerns

The primary driver of this heat wave is a large area of high pressure, often referred to as a “heat dome,” which is trapping warm air and preventing cooler air from circulating . This phenomenon, while not novel, is producing higher temperatures due to a progressively warming climate. The early heat is also contributing to faster snowmelt and drying vegetation, increasing the risk of wildfires and exacerbating drought conditions in the Southwest .

Duration and Forecast

The heat wave is expected to persist through the weekend, with temperatures challenging or breaking daily and monthly records. In Los Angeles, heat warnings and advisories are in effect through March 20th . While the heat dome is expected to weaken next week, the unusually warm conditions are likely to have lasting impacts on water resources and the potential for an early fire season.