Thus, the daily snowfall is 7.0 inches (measured to the nearest tenth of an inch) (17.8 cm), while the snow depth at observation is rounded up from 2.6 inches (6.6 cm) to 3 inches (7.6 cm). Freezing rain is never added to the daily snowfall total because it is in liquid form when it reaches the ground. Do the same with the sleet and this will add an inch (2.5 cm) to the snowfall-technically, "solid precipitation"-total. ![]() In this situation, when the snow transitions to sleet, the snow board should be cleared and the maximum depth of snow recorded-6 inches (15 cm) in this case. Looks like a lot of snow – but how to quantify that? Credit: JillWellington What should be listed as the daily snowfall? The snow depth? Then, on top of that falls an inch of freezing rain which further compacts the snow to 2.6-inch (6.6-cm) depth by the end of the observation period. Imagine 6.0 inches (15 cm) of snow falls, then an inch (2.5 cm) of sleet which compacts the snow to a 4-inch (10-cm) depth. Here in the eastern U.S., we often have to deal with snow that changes to rain during the course of a storm. So, let's consider three common scenarios. Keeping in mind that consistency is critical, the goal here is to make an accurate measurement that is representative of the surrounding area and consistent with others making snowfall measurements. The National Weather Service suggests the use of a snow board, which is a white surface that will absorb very little sunlight and stay close to the ambient air temperature. As with snow depth, you want to avoid areas of drifting when you're measuring snowfall. To properly measure snowfall, you need a flat, level surface. 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. Snowfall is the amount of snow that accumulates during a given time, usually a 24-hour period. Also, hydrologists' models that are used to predict water levels critically depend upon good initial data collection, though improved satellite data has helped reduce their reliance on any individual measurement. As hard as it is to believe at times, the snow will eventually melt, and rapid melting could cause problems with flooding. I like 10 because it makes the math easy.Ĭareful measurement is vital in order to make reasonable estimates for the amount of liquid contained in the snowpack. 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. It's usually rounded to the nearest whole number. Snow depth should be a measure of the average depth in a given location and its immediate surroundings. Snow measurement is inherently inexact, but attending to one's surroundings and sticking to the guidelines help those of us who do it on a regular basis stay consistent-and with long-term weather records, consistency is arguably just as important as accuracy.įirst, you need to understand the difference between snow depth and snowfall. ![]() There are over 8,700 cooperative observers across the country who send in their weather data to the NWS daily, some who have done it for over 75 years! National Weather Service has relied on a network of volunteer observers, all strictly adhering to the NWS guidelines, to come up with snow measurement numbers over a region. It's a little more complicated than you might think to get those oh-so-important snow totals for winter storms. Impressive numbers, for sure, but assuming you have a measuring stick long enough to reach the ground beneath all the white, how hard can it be to measure? You stick a ruler or yardstick into the snow and get a number, right? Well, not so fast.
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