## How Far Away Is A Lightning?

Next time you’re stuck in a thunderstorm, try this easy way to calculate how far away you are from lightning strikes.

Just count the number of seconds that pass between a flash of lightning and the crack of thunder that follows it, then divide that number by five.

The resulting number will tell you how many miles away you are from where lightning just struck.

Five seconds, for example, indicates the lightning struck 1 mile away, and a 10-second gap means the lightning was 2 miles away.

This technique is called the “flash-to-bang” method, and it can keep you safe during rainy summer weather.

The National Weather Service recommends taking cover if the time between the lightning flash and the rumble of thunder is 30 seconds or less, which indicates the lightning is about 6 miles away or closer.

This method is based on the fact that light travels much faster than sound through the atmosphere: Light travels at 186,291 miles per second (299,800 km/s), whereas the speed of sound is only about 1,088 feet per second (332 meters per second), depending on air temperature.

For metric-system conversions, follow this method: Sound travels at about 340 m/s, so multiply the number of seconds you counted by 340, and you’ll know how many meters away lightning struck.

A three-second count, then, would place the lightning strike about 1,020 m away, or roughly 1 km.

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## Scientists Study Winter Storms Involving Thundersnow To Pinpoint Where Heavy Snowfalls May Occur

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 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 15 centimeters of snow will fall within 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 20 centimeters falling at a rate of 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.

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.

In the U.S. thundersnow is most likely to form in mountainous regions like the Rockies as well as in the vicinity of comparatively warm and large bodies of water such as the Great Lakes.

Snow requires a cold environment, adequate moisture to form clouds, and rising air; thundersnow makes an appearance when a fourth ingredient is added: thermal instability, which is created by the addition of relatively warm air.

Market last month joined a team of storm-chasing University of Illinois at Urbana–Champaign researchers using various radars to examine what takes place inside storm clouds to cause snowfall.

The team is surveying atmospheric conditions in several locations in Indiana, Illinois and Wisconsin.

A field mill, a device that measures electric fields near the ground, will be used to determine whether there is an accumulation of charged ice particles in the clouds above.

The team next year plans to fly into snowstorms in NWS planes and drop parcels containing thermometers, barometers and other devices that, like weather balloons, will measure temperature on their way down.

If the team encounters thundersnow during its study, it may be able to confirm the conditions needed to produce it, making such icy tempests easier to forecast.

With some lead time, [be it] hours or even a day or two,” Stuart says, “we can see a big storm and predict which areas will see extreme snowfall.