Some Loudoun County residents may need to cover up their plants tonight: The National Weather Service has issued a freeze watch for late Friday night into Saturday morning for areas north and west of Washington, D.C.

The National Weather Service predicts Loudoun County could see temperatures dip into the high 20s and low 30s. Unprotected plants sensitive to freezing temperatures will be at risk, NWS said in a bulletin, as sub-freezing temperatures can kill crops and other sensitive vegetation. Residents can bring plants inside or cover them with a sheet and remove the cover when the sun comes out and temperatures rise.

National Weather Service meteorologist Kevin Witt said Thursday most of Fairfax County will probably see lows around 37 to 39 degrees. Northern and western parts of the county up toward Vienna, Reston and Great Falls could be the areas that join Loudoun in a freeze, Witt said.

The Potomac River acts as something of a moderator because of the moisture there keeping freezing temperatures at bay, Witt noted.

In addition to Northern Virginia, other general areas affected by the Freeze Watch are Washington, D.C., central Maryland and eastern West Virginia.