Montgomery and Loudoun counties and counties to their north and west are included in the freeze watch, effective late Friday night through Saturday morning. Temperatures are expected to dip into the upper 20s and lower 30s.
“Unprotected vegetation sensitive to freezing temperatures will be at risk” the National Weather Service cautions.
In the District and to the southeast, a frost or freeze is not likely, with low temperatures mainly in the upper 30s to near 40 early Saturday.
In terms of the areas most at risk for freezing temperatures, I’d draw a line from Columbia to Rockville to Sterling. Locations to the north and west of that line are most likely to experience freezing temperatures.