A Winter Weather Advisory will be issued by the National Weather Service for any amount of freezing rain, or when 2 to 4 inches of snow (alone or in combination with sleet and freezing rain), is expected to cause a significant inconvenience, but not serious enough to warrant a warning.
Some specific conditions and geographic locations may activate a Winter Weather Advisory. For example, in the Baltimore/Washington DC area, if the freezing precipitation event is expected to impact the Baltimore/Washington metro areas during rush hours (4-9 am or 2-7 pm on weekdays) forecasted snow totals of one inch will necessitate the issuance of a winter weather advisory. The snow/sleet criteria for a Winter Weather Advisory for the five westernmost counties (Allegany, Mineral, Grant, Pendleton, and Highland) is higher (3-5 inches).
See also … Arlingtoncardinal.com/snow