The National Weather Service says a cold front that was moving through the area on Sunday will be followed by a large chilly air mass. That will drop overnight lows into the high 20s and low 30s in most areas.
That's spurred forecasters to issue a frost advisory for most of southern New Jersey, Delaware, and the Philadelphia area, which will be in effect Monday from 2 a.m. to 8 a.m.
Meanwhile, a freeze warning has been issued for most northern Jersey counties, which will be in effect from midnight Sunday to 10 a.m. Monday.
Forecasters say the colder temperatures could damage or kill crops and sensitive vegetation. They urge residents to move plants indoors if possible.