How To Measure Fresh Snowfall With The TROPO Gauge
Calculating SWE By Melted Snow
Remove the top cap/funnel during periods of snow to allow snow to fall directly into the outer tube. Do NOT use the measurement labels on the outer tube for determining the depth of fresh/new snowfall, instead make a number (5-10) of snowfall measurements using a ruler or measuring stick on a snow measurement board or other level, undisturbed surface to compute a representative average fresh snowfall depth. For determining the fresh/new snow water equivalent (SWE), gather a snow core sample of the fresh/new snow with the TROPO gauge at a spot with the representative snow depth. Allow the snow to melt, then pour it carefully into the inner tube to compute the SWE. Use a premeasured amount of warm water to expedite the melting of the snow core sample in the outer tube. Remember to measure and subtract the amount of warm water from the total for determining the SWE.
Calculating SWE By Weight
Alternatively, SWE can very easily and accurately be determined by weight. First, use a kitchen scale to determine the weight of the dry, empty outer tube; write the weight down on the bottom of the tube for future reference. When the outer tube contains snow, weigh it and subtract the dry weight of the tube to determine the weight of the snow. To compute the SWE, take the weight of snow in grams and divide it by 206 g or weight in ounces divided by 7.27 oz. For example, if the snow weighed 80 g (2.8 oz), the SWE would be 80 g divided by 206 g or 2.8 oz divided by 7.27 oz which both equate to 0.39 inches (9.9 mm).
Additional Tips
Accurately measuring snow is oftentimes very difficult, especially during windy conditions. The relatively small opening on the TROPO gauge is not large enough to capture a representative depth of fresh snow, but still determine the liquid equivalent in your gauge. Compare this measurement to the SWE from a core sample at a location that represents the average of 5-10 fresh snowfall measurements around your property. If the gauge catch and independent core SWE are similar, you know you’ve got a good, representative measurement of the water equivalent. If the measurements vary considerably, then it’s best to consider the core SWE a more accurate representation of the precipitation and ignore the gauge catch. For more tips on measuring snow, visit the CoCoRaHS training videos.
