This word has been in wide use around the Chicago area since I was a kid in the 1960s. It is the nasty black conglomerate of snow, ice, soot and car exhaust particles that forms underneath your car or truck after weeks of constant sub-freezing weather.
In Chicago, snard is an ever present visual reminder of how depressing winter can be.
You can near the unmistakable sound from the alley of someone knocking snard from their car.
Snard is the number one reason for rusting undercarriages in UP Michigan.
Snard makes car wash operations rich.
Snard is about the yukkiest stuff ever.
People down here in Maryland have no concept of what snard is. They are lucky.