When winter suddenly materializes over parts of the country largely spared so far this season, it may arrive in the form of thundersnow. And if it does, a new study suggests, people better have the shovels and plows ready.
Snow accumulations of 6 inches or more are almost guaranteed when a snowstorm is accompanied by lightning and thunder, according to an analysis of 30 years' worth of Midwest storms by researchers at the University of Missouri-Columbia.
"The thunder and lightning are the attention grabbers, but when they occur in a winter storm, someone close by is receiving a significant amount of snow," said Patrick Market, an associate professor of atmospheric science who has been studying the storms under a National Science Foundation grant.
Although it's known that at any given moment 2,000 thunderstorms are occurring around the globe, the combination of warm, moist air being forced upward into cold regions to condense, freeze and stay frozen as snow and ice as it comes down is thought to be pretty rare.
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Market said reports of the phenomenon are most common in Missouri, Kansas, Colorado, Nebraska, Iowa, Minnesota, Oklahoma and northern Texas.
And many people may have been in a thundersnow storm and not realized it, since the snow muffles the sound of thunder and obscures the lightning down to a few miles, producing a much smaller signature than summer squalls.
Still, a thundersnow storm can leave a big impression when it comes. A January 1994 storm marked by flashes and rumbles socked Louisville, Ky., with 2 feet of snow.
On Dec. 9, 2005, a sudden blizzard accompanied by lightning and thunder produced snowfall rates of up to 5 inches an hour over parts of northern Massachusetts and southern New Hampshire.
And just last month, the second big Plains snowstorm in a week featured thundersnow and dumped nearly 2 feet on northeastern Kansas.
Official weather records recorded only about 375 thundersnow events in the United States between 1961 and 1990.
For the new study, Market and Christina Crowe, an undergraduate student in meteor- ology, focused on 22 storms in the upper Midwest during that period.
Using snowfall totals from airport weather stations and reports from National Weather Service volunteer spotters, they found that in 19 of the 22 storms there was boot-deep snowfall in some portions of the affected areas within a 24-hour period.
Six or more inches of snow fell in 86 percent of the storms, and almost half the storms led to 10 or more inches, according to the report in the Dec. 22 issue of the journal Geophysical Research Letters.
Crowe and Market said they hope the data will help forecasters more accurately predict accumulations during snowstorms.
"If forecasters see there's thundersnow, they will know there's a greater chance for heavy snow in their area," Crowe said.
"It signifies that that storm is a snow producer."
