A dangerous heat wave will bring record-breaking temperatures to parts of the Western U.S. this weekend, prompting warnings for people to stay inside and heightening wildfire risks in areas that already are dry or burning.

A ridge of high pressure is holding heat close to the ground — what’s known as a heat dome — from Arizona to Montana, though the good news is that it will be relatively short-lived, National Weather Service meteorologists said.

The National Weather Service on Saturday forecast a high of 115 degrees Fahrenheit (46 degrees Celsius) in Las Vegas, the hottest temperature of the year.

Phoenix is expected to reach 116F (47C), while El Centro, California, was expected to hit a record 118F (48C). Even parts of Montana were expected to broil, with a record 104F (40C) forecast for Great Falls.

In Las Vegas, Saturday’s forecast high was 10 degrees above normal, with meteorologists warning of dangerous heat through Sunday, when the high is expected to be 114, said weather service meteorologist Morgan Stessman.

Overnight lows in the upper 80s to low 90s will make the situation especially dangerous because it doesn’t allow people’s bodies to recover.

“There’s just no relief overnight,” Stessman said.