Historic October heat in the West, made possible by climate change

Human-caused climate change is making it more likely that extreme heat will continue into the fall, with record-breaking temperatures hitting much of the western United States in October

The West is experiencing an unprecedented late-season heat wave, with October temperatures broken in major cities, some of which are still recording triple-digit heat levels.

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

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

Even hotter conditions are expected in some regions on Wednesday. Heat warnings have been issued across California, Arizona and Nevada. Excessive heat warnings are also in effect for San Francisco, Las Vegas and Phoenix, and a heat warning 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 90 degrees.

If Denver hits the 90s, records show it will be the highest temperature of 90 degrees ever recorded in the city.

Record-breaking heat is expected to last into the weekend across most of the West.

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

According to climate researchers, human-caused climate change is increasing the frequency and intensity of extreme heat events.

According to the federal government's fifth national climate assessment released last November, the average number of heat waves experienced by major U.S. cities each year has doubled since the 1980s.

The record high October temperatures reached Monday in Palm Springs and Phoenix were made at least five times more likely by human-fueled climate change, according to Climate Central's Climate Shift Index.

Global warming also contributes to extreme heat that lasts well into the fall.

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

Fall warming is widespread across the contiguous U.S. and strongest in the Southwest, according to an analysis by Climate Central.

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