How Snowfall Is Measured
Snowfall is the depth of new snow that has fallen, measured to the nearest tenth of an inch. It is different from snow depth, which is the total amount of snow on the ground.
The snow board
Observers place a flat white board on the ground in an open area away from buildings and trees. They measure the new snow on the board with a ruler, then wipe it clean. The National Weather Service recommends measuring no more than once every six hours. Measuring more often makes totals higher, because the snow has less time to settle.
Storm totals and daily totals
Most reports you see during a storm are storm totals: everything that has fallen since the snow started. Climate records use daily totals from midnight to midnight, so the official amount for a day can differ from a storm total that spans two days.
Who reports snowfall?
- Trained SKYWARN storm spotters
- CoCoRaHS volunteers (a nationwide network of backyard observers)
- NWS cooperative observers and staff
- Airports and automated stations (often estimated from liquid precipitation)
Why do nearby totals differ?
Elevation, lake-effect bands, coastal rain-snow lines and measuring time can change totals by many inches within a few miles. A town on a hill can easily report double what the valley below receives.