Records could be broken from Southern California all the way up to portions of Washington and Montana.
In California’s Central Valley, high temperatures will run 15 to 20 degrees above normal.
Triple-digit heat will be widespread across the lower elevations, with afternoon highs forecast to range from 101 to 107 degrees.
In Northern California, “highs will range from 20 to 25 degrees above climatology for this time of year,” said the National Weather Service office in Sacramento.
High temperatures are expected to top out around 106 in the Sacramento metro area and possibly reach 108 to 109 in the northern Sacramento Valley.
Temperatures will be in the mid- to upper-90s across portions of Montana this week. “There is high confidence that Wednesday’s high temperatures could reach well into the mid to upper 90s for western Montana valleys, with 90s to near-or-above 100 degrees for central Idaho valleys,” said the weather service in Missoula.
Areas around Las Vegas and Death Valley could see its first 100-degree day of the year this week.
“Hottest days will be Wednesday and Thursday with highs reaching within a couple degrees of daily records for some areas,” said the weather service office in Las Vegas.