Several hours of temperatures at or below freezing are expected across the area tonight, with low temperatures in the mid to upper 20s likely, especailly along and east of the James River Valley. Below is a map of forecast lows for tonight/early Sunday morning.
For many, the impending killing freeze will be 1 to 2 weeks ahead of schedule for a typical autumn season. Using data from 1981-2010, the median date of the first 28°F or colder temperature falls during the first week of October, as seen in the graphic below from the Midwestern Regional Climate Center. (NOTE: Median date for the first occurrence of 28°F means that 1/2 of the years saw 28°F prior to the indicated date, while the other 1/2 occurred after that date.)
You can monitor which locations have already experienced freezing temperatures via the Midwest Climate Watch Freeze Maps, also provided by the Midwestern Regional Climate Center.