* WHAT...Sub-freezing temperatures in the upper 20s and low 30s are possible.
* WHERE...Portions of north central and western Maryland, central, northwest, and western Virginia, and the eastern panhandle of West Virginia.
* WHEN...From 1 AM to 8 AM EDT Sunday.
* IMPACTS...Frost and freeze conditions could kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing.