SIDNEY — The National Weather Service in Cheyenne upgraded a freeze watch to a freeze warning for portions of western Nebraska and northeast Colorado, with sub-freezing temperatures expected overnight Saturday into Sunday morning.

The warning includes Cheyenne, Logan, Morrill, Sedgwick and Scotts Bluff counties and will be in effect from midnight to 7 a.m. Sunday. Forecasters said temperatures could drop as low as 21 degrees as a strong cold front moves through the region.

The weather service warned frost and freeze conditions could kill crops, damage sensitive vegetation and harm unprotected outdoor plumbing. Residents are encouraged to take steps now to protect plants and water systems before the cold sets in.

Strong winds are expected to return Sunday afternoon and continue into early next week, with breezy conditions persisting through Monday.