US west coast prepares for 'dangerous' heatwave in early spring

March 17, 2026

An unusually early and intense heatwave is gripping the southwestern United States this week, with a high-pressure heat dome causing temperatures to soar 20-30 degrees Fahrenheit above normal levels. Phoenix may experience triple-digit temperatures as early as Wednesday, marking the earliest such occurrence in nearly forty years, while various locations across California, Nevada, and Arizona could see readings between 90-110°F. The prolonged extreme heat threatens California's diminished snowpack by accelerating melt in the Sierra Nevada mountains, which could lead to summer water shortages and an extended wildfire season since snowpack provides approximately one-third of the state's water supply.

Who is affected

Millions of residents across the southwestern United States
Residents of Phoenix, Arizona
Communities throughout California, Nevada, and Arizona
Elderly and other at-risk groups in affected areas
Tourists and visitors traveling from cooler climates
Residents of the Bay Area and central coast of California
Communities dependent on California's water supply and snowpack
Areas from the Rockies to the High Plains facing elevated wildfire risk

What action is being taken

The National Weather Service is forecasting and monitoring temperatures
NWS has issued heat advisories for parts of California, including the Bay Area and central coast
Residents are being warned to check on elderly and at-risk groups
Residents are being advised to schedule events around peak heat times
The Las Vegas NWS office is issuing warnings about heat dangers for tourists and non-acclimated individuals

Why it matters

This heatwave is significant because it represents the earliest arrival of extreme heat to the region in nearly four decades, occurring during a period when temperatures should still be relatively mild. The timing is particularly critical for California's already below-average snowpack, as accelerated melting in the Sierra Nevada will reduce gradual water release into reservoirs throughout the year, threatening summer water availability since snowpack provides roughly one-third of the state's water supply. The early onset of extreme heat also increases the risk of a longer and more severe wildfire season as landscapes dry out prematurely, while posing immediate health dangers to millions of residents, especially vulnerable populations and tourists unaccustomed to such conditions.

What's next

The heat is expected to persist for several days
Only gradual relief is possible by the weekend or early next week
Above-average temperatures are expected to spread across much of the United States by the end of the week and into next week

Read full article from source: BBC