How to Measure Snowfall Correctly
Accurate Measurements are More Than Sticking a Ruler in the Ground
Nov 13, 2008
For those interested in weather, keeping a log of local weather conditions is often a hobby. While the data collected in most cases is for his or her own enjoyment, some offer their data to forecasters and researchers, which in turn use the data to improve the understanding of local climates.
It is for this reason that accuracy in measurements is important. If everyone was using a different method, the readings gathered will have less relevance and in turn will be all but useless for purposes of research.
In this article, the best practices for measuring snowfall are discussed, focusing on methods encouraged by the National Weather Service for its network of spotters and observers.
Using a Snowboard for Accurate Snowfall Measurements
Forecasters agree that the most accurate method for measuring snowfall (that is what is currently falling: there is a difference) is by using something called a "snowboard." Essentially this is a piece of wood about 16" by 16" that is painted white.
Measuring from the ground is not good practice, say forecasters, because the blades of grass may actually hold the snow above the actual ground, which will in turn artificially inflate readings.
Generally it is agreed that snowboards should be wiped clean every six hours or so to prevent the natural settling of fallen snow from occurring. In addition, these should be placed well away from structures and obstructions -- about 20 to 30 feet if possible -- in order to prevent drifting from inflating the totals as well.
Taking the Actual Measurement Correctly
The process of taking the actual measurement is pretty straightforward. Stick a ruler into the fallen snow and read the measurement. Typically the NWS measures snowfall to the tenth of an inch, although this may be difficult with a standard ruler.
The fractional portion should be changed to a numeric value, and rounded up if need be. Thus for example, If one measures 5 1/4 inches, that would be rounded up to 5.3 inches, and so forth. Another concern is blowing and drifting, which should be taken into account if it has occurred.
In that case, take several measurements on the measuring surface and then average them together for a more representative total.
Snow Depth is a Different Measurement
Another useful statistic to the weather watcher is something called snow depth. This is the measurement of total snow on the ground, which could include several different snowstorms. When measuring snow depth, another snowboard can be used, although the National Weather Service seems to indicate here that using the ground is okay.
Take several different measurements and average them together in order to get the snow depth. It should also be noted that if there is any bare ground, at least one of the measurements should be zero in order to account for that.
CoCoRaHS, a network of precipitation observers, describes it this way: "For example, if half the ground has 2" of old snow and the other half of the ground is already bare, the average snowdepth would be 1"."
Accuracy and Honesty are Key
If there is one golden rule among observers, it is accuracy and honesty, especially the latter. No one benefits from artificially inflated totals just to be the person with the most snow when they report. While seeing one's reports in the news and elsewhere is a thrill, its worthless if it is not accurate.
Thus, following these guidelines will ensure that one's snowfall measurements are useful not only for themselves, but the weather forecasters who may use them as well.
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