UPDATE: The National Weather Service has added Fairfax County to the Freeze Watch for Friday night going into Saturday morning.
"Fairfax is now under the Freeze Watch too," said National Weather Service meteorologist Christopher Strong, in an e-mail to Patch. "The general theory of a watch is that there is a 50 percent chance or better than it's going to happen, and then a warning when we are nearly certain."
The earliest freeze (32 F) at Dulles Airport (est. 1962) was Sept. 24, 1983, Strong said. The latest was Nov. 11, 2005, he noted. If there is a freeze, "we would be a little early, but not too far off a typical first freeze date."
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.
National Weather Service meteorologist Kevin Witt said Thursday "it looks like the eastern and southern parts of the county are out of it, but Fairfax City and west could see freezing or near freezing temperatures."
Most of the county will probably see lows around 37 to 39 degrees, Witt said. Northern and western parts of the county up toward Vienna, Reston and Great Falls could be the areas that could see 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.
The 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. 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.
In addition to Northern Virginia, other general areas affected by the Freeze Watch are Washington, D.C., central Maryland and eastern West Virginia.