The National Weather Service is warning of the dangers of a “flash freeze” by noon on Sunday.
On the North Shore, the temperature was below freezing at 9 a.m. Earlier in the morning, the temperature had risen to 35 degrees and it was raining.
The fluffy, light snow that fell overnight had been packed down and turned slushy.
“Winds will be shifting to the north and northwest over the next few hours allowing colder air to work back into the region and temperatures will fall below freezing,” the weather service said in issuing its alert. “Standing water will freeze and areas of black ice may develop on roadways.”
Drivers should expect “rapidly deteriorating road conditions” and potentially black ice, the weather service said.