Here’s some interesting information about how snowfall and snow depth is measured. If you want to know the official snow measurement guidelines from NOAA then check out their handbook that the volunteers who measure the snow use.
This is a portion of an article by Bill Syrette
How deep is your snow
Snow depth should be a measure of the average depth in a given location and its immediate surroundings. It’s usually rounded to the nearest whole number. To get a representative number, you need a site with minimal drifting (not always easy to find) and several measurements should be averaged to get a final number. I like 10 because it makes the math easy.
Careful measurement is vital so we can make reasonable estimates for the amount of liquid contained in the snowpack. As hard as it is to believe at times, the snow will eventually melt, and rapid melting could cause problems with flooding. Also, hydrologists’ models to predict water levels critically depend upon good initial data collection (though improved satellite data has helped reduce their reliance on any individual measurement).
Snow depth is like the sum of individual snowfalls, if one assumes no sublimation – snow turning into water vapor – or melting from the first snowfall until the present day. That assumption would almost always be wrong, of course, but if we suspend reality for a moment, the depth will still never exceed the sum of all snowfalls because snow is compressible. So, two 10.5-inch snowfalls may only accumulate to a depth of 17 inches. It’s the compressibility of snow that causes the greatest consternation and controversy with snowfall measurement.
How much snow did a storm bring
Snowfall is the amount of snow that accumulates during a given time, usually a 24-hour period. In a perfect world this 24-hour period would end at midnight, but the vast majority of National Weather Service cooperative observers take their daily observation in the morning.
To properly measure snowfall, you need a level and flat surface. As with snow depth, measuring snowfall should be unaffected by drifting. The National Weather Service suggests the use of a snowboard, which is a white surface that will absorb very little sunlight and stay close to the ambient air temperature, but any “cold” surface will do. Keeping in mind that consistency is critical, the goal here is to make a measurement that is representative of the surrounding area and consistent with others making snowfall measurements.