West heats up amid historic heatwave

This weekend, nearly 40 million people in the western U.S. will experience heat made at least three times more likely because of climate change. This follows ongoing record-breaking temperatures across the United States. So far this July, over half of the U.S. population has experienced heat made at least three times more likely by climate change.

How unusual is this weekend’s forecasted heat?

• Daily average temperatures are expected to reach Climate Shift Index (CSI) levels of 5 in southern California, Nevada, Utah, Arizona, southwestern Colorado, southern Idaho, and northern Washington in the U.S. along with portions of British Columbia, Alberta, Saskatchewan, and westernmost Manitoba in Canada. A CSI level 5 indicates that human-caused climate change made this excessive heat at least 5 times more likely, signifying an exceptional climate change event.

• Excessive Heat Watches and Warnings and Heat Advisories have been issued for parts of California, Arizona, Nevada, Washington, Oregon, and Idaho with dangerously hot conditions expected Friday through the upcoming weekend.  

• The persistent heat dome responsible for this historic heat in California will expand across the western U.S. over the next several days to impact nearly 40 million people.

• Temperatures 20°F to 35°F above normal are anticipated across much of the Interior West, with forecasted highs in the 95°F to 105°F range and nighttime temperatures of 70°F to 75°F.

• Excessively hot temperatures, up to 116°F, are expected in portions of the San Joaquin Valley, southwestern Arizona, and eastern Washington.

• In Canada, nearly all provinces and one territory will experience anomalous heat this weekend that is forecast to persist into next week. High temperatures as hot as 35°C and nighttime temperatures above 18°C are expected. 

• There is a 60 percent probability that excessive heat will continue during the week of July 22 to 26. While temperatures are expected to decrease across the Pacific Northwest, this persistent heat is expected to endure in the Desert Southwest.

Use the Climate Shift Index global map to see CSI levels in your city and region, and see our FAQs to learn about the CSI in both English and Spanish. 

Many cities will experience extended periods of extreme heat. Download data here for cities most impacted.

How intense is the ongoing heat?

• From July 2-17, 209 million people in the U.S. experienced at least one day with CSI level 3.

• In California, Nevada, Utah, Colorado, Arizona, and New Mexico, a total of 39 million people experienced at least one day with CSI level 3.

• This extreme heat event follows several weeks of record-breaking temperatures across California’s Central Valley — where cities including Fresno, Bakersfield, Madera, and Hanford — recorded ten or more consecutive days with highs at or above 105°F.

What do experts say?

Dr. Andrew Pershing, vice president for science at Climate Central, said: 

“This ongoing severe heat event is linked directly to climate change,” said Pershing. “As the western U.S. and Canada gear up for another sweltering weekend, it is a stark reminder of the effects of carbon pollution.”

To request an interview with a Climate Central scientist, please contact Abbie Veitch at aveitch@climatecentral.org