Wild Winter Weather: Why Is Thundersnow So Rare?

Jan. 27, 2011— -- As if the sheer volume of snow dumped by last night's record-breaking storm wasn't shocking enough, East Coasters had front row seats to the rare weather phenomenon known as thundersnow.

From New York to Philadelphia to Washington, D.C., snowbound residents reported rumbles of thunder and bursts of lightning as the sixth storm in the past 30 days rolled through the region.

On Twitter, the mysterious meteorological event spawned a flurry of perplexed posts as people wondered what was going on with the unusually dramatic weather.

"Snow + thunder = snunder!! Mother nature is p***ed," wrote one Twitter user.

"Ok so we have a foot of snow and now thunder and lightning??? Pretty sure that means something bad...." posted another.

Other weather watchers had some fun playing around with the name of the seemingly freakish phenomenon.

What Is Thundersnow?

One Washingtonian wrote ""Thunder Snow" would make a great sports team name. ('The New York Thunder Snow takes their winning streak on the road..')"

"Thunder snow should be an episode of flight of the concords," said a Twitter fan in Philadelphia.

But though thundersnow storms may be rare, meteorology experts say they are legitimate weather events with some predictive value for forecasters.

Robert Kelly, chief of forecast operations at the National Oceanic and Atmospheric Association (NOAA), said that the dynamics behind thundersnow are similar to the dynamics of any thunderstorm -- a strong, upward motion of warm, moist air.

The combination of warmer temperatures at the ground and cooler temperatures higher up generate thunder and lightning, he said. But those dramatic weather events rarely accompany snow because warm ground temperatures usually don't occur during snowstorms.

Thundersnow May Predict Significant Snowfall

"But in the case like we had yesterday, even though temperatures near the surface were in the low 30s, it was really warm as a wintertime snow temperature," he said. "And we had a shot of very cold air that shot through -- it created that strong temperature lapse rate which generated a lot of electrical motion."

The mix of ingredients necessary for thundersnow is so uncommon that experts have estimated that only .07 percent of snowstorms are associated with thunder.

Patrick Market, an associate professor of atmospheric science at the University of Missouri, said that in a given year, only half a dozen to a dozen thundersnow events are reported in the eastern two-thirds of the U.S. The Rocky Mountains and the Great Lakes areas are considered the most prone to the rare storms.

But he said that though the storms are rare, scientists have found some indication that lightning during snowstorms inidicates a significant snowfall at some point during the storm system.

In a 30-year study of winter storms involving lightning and snow, Market and other University of Missouri researchers found that there is an 86 percent chance that at least six inches of snow will fall within 70 miles of the flash.

"Thunder and lightning existing in the storm are usually a symptom of something else," he said. "That's usually a harbinger of somebody getting a significant snowfall later on."