The overnight low in the Boise area is forecast to dip to 4 degrees below zero, according to the National Weather Service.
"It's going to be very cold. It's going to get frigid," said David Groenert, a meteorologist at the Boise Airport.
Even so, that won't be anywhere near the record for the date. It was 19 below on Dec. 8, 1972. That year, several school districts closed schools when the diesel in their buses jelled up and could not be started.
Sunday's high is expected to only climb to 18 degrees under sunny skies. And then the temperature is predicted to reach 4 below again Sunday night.
"The cold air is going to stick around for a few days," Groenert said. "It's not going to rise above freezing until Thursday, when the temperature will reach 37 degrees."
A total of 2.3 inches of snow fell at the Boise Airport early Saturday. There's a chance of snow late this afternoon, but through Wednesday, it will be sunny or partly cloudy. Clear skies allow daytime heat to escape and makes for colder nights.
Icy conditions led to four dozen wrecks and vehicles sliding off Ada County roads during a 13-hour period from 12:01 a.m. Saturday to 1 p.m., according to statistics complied by dispatchers with the Ada County Sheriff's Office.
Only one of those crashes resulted in injuries, said Andrea Dearden, a sheriff's spokeswoman. There were 32 non-injury crashes, 4 hit-and-runs and 11 incidents where vehicles slid off the road, she said.
Motorists are reminded to slow down, leave extra space between vehicles and use extra caution when roads are covered by snow or ice.