Because I think it is a damn near guarantee many of us will be in one on Thursday night/Friday here is the criteria for a blizzard warning. Big note-it has nothing to do with amount of snow fallen, it is wind speed and visibility based.
"The NWS issues a Blizzard Warning when falling and/or blowing snow combines with strong winds to create dangerously low visibility over at least a three hour period. The threshold for wind is frequent gusts over 30 knots and visibility is frequently less than a quarter mile."
And a great recent article from the GOAT of weather data Daryl Herzman.
Iowa Environmental Mesonet of Iowa State University
mesonet.agron.iastate.edu