* WHAT...Sub-freezing temperatures as low as 30 degrees expected. * WHERE...In New Jersey, Morris, Somerset, and Hunterdon Counties. In Pennsylvania, Berks, Lehigh, Upper Bucks, Western Chester, and Western Montgomery Counties. * WHEN...From midnight tonight to 9 AM EDT Saturday. * IMPACTS...Frost and freeze conditions could kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing. Take steps now to protect tender plants from the cold.