By The start of October is bringing little relief to parts of the western United States, where 36 million people are under heat alerts and sweltering temperatures are setting records into the fall.
Excessive heat warnings are in place in Arizona, California and Nevada, where high temperatures are expected to be 10 to 25 degrees Fahrenheit hotter than normal.
On Tuesday, Phoenix reached 113 F, making it the hottest October day in the city’s recorded history. Before this week, Phoenix had never recorded a high temperature over 110 F in the month of October.
Further north, San Francisco reached 94 F on Tuesday, which was the city’s hottest day in two years. Las Vegas on Tuesday came just 1 degree shy of matching a daily heat record of 103 F set on Oct. 1, 1978, according to the National Weather Service.
The hot conditions are expected to persist over the coming days. Dozens of heat records could be set through the weekend from California to Colorado, including in Lake Tahoe, Reno, Las Vegas, Colorado Springs and Denver.
October’s warm start follows a summer of extreme temperatures. Both Arizona and California had their warmest summers on record in 2024, according to the National Oceanic and Atmospheric Administration.
Extreme heat is expected to worsen as a result of climate change. Studies have shown that as the planet warms, heat waves will become more likely, more intense and longer lasting.
The unseasonable warmth could stick around deeper into autumn. The NOAA’s Climate Prediction Center has said there is a 50% chance that much of the West could see above-average temperatures through the month of October.
High heat extending from California into the central Rockies and the northern Plains will also increase the risk of wildfires, according to the weather service. Red flag warnings, put in place to alert for critical fire danger, are in effect in Colorado, Montana, Nebraska, South Dakota and Wyoming.
