* WHAT...Sub-freezing temperatures as low as 28 expected. * WHERE...Northern Mendocino Interior, and Northern Lake. * WHEN...From 1 AM to 9 AM PDT Thursday. * 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. To prevent water pipes from freezing; wrap or drain or allow them to drip slowly.