Our recent October storm created an ideal opportunity to show how difficult it can be to measure snow accurately. Snow accumulation is the goal, which means there is no effort made to measure snow that does not accumulate.
Snow that melts as it falls counts for moisture but not for snow accumulation. Un-flattened grass in the fall may inflate the apparent accumulation.
Snow falling in freezing weather does not melt, but it does compact.
Drifting snow makes the compaction worse, and the snow observer must take numerous readings to form an average. Because snow compacts as it falls, it should be swept away from the measuring surface and then re-measured no more than once every six hours for as long as the snow continues.
Water content of a snowfall is more straightforward. Snow in a flat-sided can is melted and then measured. The tricky part here is to place the can in a good spot to catch the right amount of snow.