Measuring Snowfall

“It was wet & white & swift and where I am
we don’t know.”

John Berryman, “Dream Song 28: Snow Line

Recent weather conditions out east provide an occasion to question the idea of facts—and by extension, information—as simply empirical. According to the Washington Post, the official count of snowfall in the D.C. area during last weekend’s blizzard will be 17.8 inches. That number comes from the weather observers at Reagan National Airport. While considerable, it amounts to considerably less snow than other observers recorded at nearby locations. “Dulles International recorded 29.3,” reports the Post, “while Thurgood Marshall-BWI Airport recorded 29.2.” Why the discrepancy? And why should we care?

The reason this bit of trivia made national news is because the observers at Reagan National deviated from standard snow measuring techniques. The standard method requires a snowboard. Not to be confused with its recreational namesake, a meteorological snowboard is a flat piece of plywood usually painted white. Taking a measurement from a snowboard helps avoid snow line inflation caused by grass while its light color helps reduce snow degradation caused by sunlight. Unfortunately, the white paint may have made it harder for observers at Reagan National to find the thing once blizzard conditions dumped a bunch of snow on it.

Mark Richards, senior weather observer at the airport, admitted to losing the board mid-storm. Without the board, the team had to resort to the unconventional method of taking several depth measurements and averaging them out to a single figure. That lower-than-expected figure could be explained as the result of snow compacting under its own weight. Or, it could be a matter of Reagan National’s regional location tending to stay warmer than its surroundings. Even unavoidable snow drift can undermine the credibility of measurements. Richards, however, stands by the official 17.8-inch measurement his team made, reminding skeptics “that measuring snow in a blizzard is a tough thing to do.” The strict guidelines for measuring snow, it turns out, prescribe an inexact science.

This minor scandal makes visible how official numbers, often taken as simple facts, derive from complex and imperfect methods of empirical observation. The snowboard method may produce more reliable standards than the averaging method, but no single number can claim to perfectly represent snowfall for the entire city. And yet, the official record stands. The consequences go beyond keeping a tally of record-breaking blizzard conditions. As  the National Weather Service stresses, snowstorms of this magnitude impact life, property, and the economy. The official record of snowfall may help determine if a region needs additional relief. In the long-term, such numbers become the so-called hard data grounding knowledge of weather patterns. That knowledge begins, though, with small teams around the country doing their best in bad conditions to measure “wet & white & swift” snow lines.

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