Late-season heatwave to bring near-record temperatures to western U.S.

A late-season heatwave is developing across the western United States, with temperatures expected to climb well above normal through the weekend and into next week.

A strong ridge of high pressure is building over the region as a wet weather pattern continues farther south. The setup is expected to push temperatures 15 to 20 degrees above seasonal averages in parts of the West.

Coastal areas and nearby urban centres are expected to see temperatures well into the 90s Fahrenheit, while some locations in California's Central Valley could reach 100 F.

The heat will be particularly persistent across southern California, where overnight temperatures are expected to remain in the mid-to-upper 70s in the Los Angeles and San Diego urban areas, providing limited relief.

Extreme heat warnings are in effect across much of coastal southern California, while heat advisories cover parts of central California.

The heat is also expected to spread northeastward over the next several days. Temperatures in the 80s and near 90 F are expected to develop across parts of the Great Basin.

The heatwave comes unusually late in the season, with the combination of daytime and nighttime temperatures expected to create prolonged heat impacts in affected areas.