Historic October heat in the West made possible by climate change

(LOS ANGELES) — Human-amplified climate change is making it more likely that extreme heat to lasts longer into fall, as record-breaking temperatures for the month of October blanket much of the western U.S.

An unprecedented late season heat wave is in effect in the West, with October temperatures broken in major cities, several of which are still experiencing triple-digit heat.

On Tuesday, Palm Springs reached 117 degrees Fahrenheit; Phoenix hit 113 degrees while Tucson got up to 105 degrees.

Elsewhere in California, San Jose broke its daily record at 100 degrees; Oakland reached 96 degrees; Napa hit a daily record at 99 degrees; and downtown San Francisco reached 94 degrees, the hottest October temperature in the city in two years.

Some regions are expected to experience even hotter conditions on Wednesday. Heat alerts have been issued throughout California, Arizona and Nevada. Excessive heat warnings are also in place for San Francisco, Las Vegas and Phoenix, and a heat advisory has been issued in Los Angeles.

The geographic range of the record heat is expected to expand eastward, including Colorado, where Denver could reach a record-high of 90 degrees.

If Denver reaches the 90s, it will be the latest 90-degree temperature ever recorded in the city, records show.

The record heat is expected to last into the weekend for most of the West.

Fire danger is also high from California to Montana due to the dry, hot and windy conditions.

Human-amplified climate change is increasing the frequency and intensity of extreme heat events, according to climate scientists.

The average number of heat waves that major U.S. cities experience each year has doubled since the 1980s, according to the federal government’s Fifth National Climate Assessment, released last November.

The record-breaking temperature for the month of October set in Palm Springs and Phoenix on Monday were made at least five times more likely by human-amplified climate change, according to Climate Central’s Climate Shift Index.

Global warming is also helping fuel extreme heat that persists well into the fall season.

Fall nights have warmed by 2.7 degrees Fahrenheit, on average, from 1970 to 2023 in 212 U.S. cities, according to a Climate Central analysis.

Fall warming is widespread across the contiguous U.S., and most intense in the Southwest, according to a Climate Central analysis.

ABC News’ Matthew Glasser and Daniel Peck contributed to this report.