The National Weather Service issues different weather advisories, watches, and warnings in the winter. All of them have different criteria that need to be met to be issued. Depending on where you live in the United States, the criteria can be different. This is a list of the criteria for Central Pennsylvania.
A Winter Storm Watch will be issued 12 to 24 hours before an event starts. A watch means that warning criteria could be met within that time span.
A Winter Storm Warning is issued when 6″ or more of snowfall is expected in a 12 hour span, or 8″ or more of snowfall is expected in 24 hrs. Also a Winter Storm Warning can be issued if .25″ of ice is expected.
A Winter Weather Advisory is issued when 3″ or more of snow is expected to fall in 12 hour span, or a trace of ice.
A Blizzard Warning is issued if winds are sustained at 35 mph with moderate snow falling or blowing for 3 hours.
A Wind Chill Warning is issued if it will feel like it is 25 degrees below zero.
A Wind Chill Advisory is issued if it will feel like 10 degrees below zero in Indiana and Jefferson County or 15 degrees below zero in the rest of Central PA.