* WHAT...Sub-freezing temperatures as low as 23 possible. * WHERE...Portions of northwest and west central Kansas and southwest Nebraska. * WHEN...From late Friday night through Saturday morning. * IMPACTS...Frost and freeze conditions could kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing. * ADDITIONAL DETAILS...Due to a warm early spring, green-up is occurring 2 to 4 weeks earlier than climatological normals and the growing season has begun.