WHITEOUT: A 30-year study of snowfall found that when lightning is observed during a snowstorm, there is an 86 percent chance that at least six inches (15 centimeters) of snow will fall within 70 miles (113 kilometers) of the flash. Image: COURTESY OF WILBANKS
It's been more than 30 years—during the Blizzard of 1978 to be exact—since Neil Stuart saw "thundersnow," a weather phenomenon featuring the unusual combination of thunder, lightning and snow. The National Weather Service (NWS) meteorologist was 10 years old, living near Boston. The storm—which he says "is famous in meteorological circles" and influenced his career path—dumped 27 inches (67 centimeters) of snow on the ground over two days. The heaviest snow, however, came during a six-hour thundersnow storm that delivered one foot of snow over a six hour period.*
Seeing thundersnow come down is "like watching a time-lapse movie of the snow building up, because it falls so quickly," Stuart says.
Thunder and lightning during a snowstorm is different from a run-of-the-mill snowstorm; it is extremely rare—fewer than 1 percent of observed snowstorms unleash thundersnow, according to a 1971 NSW study. But recorded observations of the phenomenon date back to 250 B.C., say ancient Chinese records translated in 1980 by atmospheric scientist Pao-Kuan Wang, now of the University of Wisconsin–Madison.
Today, researchers are interested in thundersnow for its predictive value. According to Patrick Market, an associate professor of atmospheric science at the University of Missouri, a 30-year study of snowfall found that when lightning is observed during a snowstorm, there is an 86 percent chance that at least six inches (15 centimeters) of snow will fall within 70 miles (113 kilometers) of the flash. Researchers are trying to determine the combo of atmospheric conditions required to create thundersnow to help them better predict heavy snowfall—which they define as at least eight inches (20 centimeters) falling at a rate of three to four inches (7.5 to 10 centimeters) per hour—and issue warnings about hazardous weather before it hits, giving people time to prepare, take cover and get off the road. (The National Highway Traffic Safety Administration estimates that more than 800 deaths were caused by snow-related traffic accidents in 2007.)
By the time the lightning flashes during a thundersnow-storm, it is often already too late to prepare local residents for the whiteout on the way. "If we're talking about the observation of thundersnow," Market says, "the predictive value is on the order of minutes to hours."
*Correction (4/06/09): This article originally stated that the 27 inches of snow accumulated over six hours instead of two days.