Rattling off snowfall amounts for various locations around your city is a staple of local news reports, and every so often you'll hear the reporter mention that the local airport saw a "trace" of snow. What exactly is a trace of snow, anyway?
Snowfall amounts in the United States are recorded in increments of one-tenth of an inch. Locations in the north often wind up seeing so much snow that numbers after the decimal point don't really matter unless you're creeping up into record territory. Snow is a little more spotty in other parts of the country, and in many locations (especially the south), that one-tenth of an inch is a big deal. A dusting of snow—a light coating on the ground that's enough to make the ground white, but hardly enough to measure—is often recorded in the books as 0.1" of snow, not a trace as many believe.
A trace of snow—denoted in records as a "T"—is when a steady snow falls but melts when it comes in contact with the ground. In other words, a trace of snow is snow that doesn't stick. The picture at the top of this post was taken by an Associated Press photographer in New York City a few years ago. The ground is just wet even though it's snowing quite heavily. Assuming the snow didn't stick to the grass, either, weather observers would record that as a trace.
A trace of snow is a record in some locations. For instance, Jacksonville, Florida, saw some ocean effect snow at the beginning of the month, and the city's airport officially recorded a trace of snow for the first time in five years. On the other hand, Champaign-Urbana, Illinois, tied a record for lowest amount of snow in the month of December last year, recording a lowly trace for only the fifth year since the local airport started keeping records.
[Images: AP, xmACIS2]