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CHASING THE SNOWSTORM

An MU meteorologist studies thundersnow, a snowstorm with thunder and lightning
Sunday, February 20, 2005 | 12:00 a.m. CST; updated 8:29 a.m. CDT, Tuesday, July 22, 2008

Spring is on the horizon, but MU meteorologist Patrick Market, on the other hand, can’t wait for the next big snowstorm.

Market, an assistant professor of atmospheric science, is working to develop an accurate way to measure snowstorms containing thunder and lightning. Known as thundersnow, these severe weather events tend to produce heavy amounts of snowfall in localized areas.

In some rural areas, such severe weather events cause residents to be stuck at home for days at a time before being plowed out. Increased risk of car accidents is another problem when large amounts of snow accumulate.

Following thundersnow storms, emergency vehicles have more difficulty getting to those in need. Predicting the storms earlier will enable city and county governments to be better prepared for snow removal needs.

“When thundersnow is present, you can receive a large amount of snow in a short period of time,” Market said.

Meteorologists from the National Center for Atmospheric Research in Boulder, Colo., have brought equipment that allows Market and his graduate research assistants to sample ice crystals forming within those storm systems.

The Colorado meteorologists have been on call for Market’s team since early February and will remain in Columbia through March 20. The six-week deployment of the center’s scientists and their equipment costs roughly $60,000, which covers everything from travel and lodging to their salaries. This cost is covered through support funds from the center.

“When a forecast shows a good possibility of a storm, we will chase it,” Market said. “Good forecasts fit patterns recognized from previous storms.”

Market hopes to chase storms four to five times within the six-week period. March is the most likely time of the year for thundersnow to occur.

“There have been 48 reports of thundersnow across the United States since Oct. 1, 2004. Most of these come from the mountains of Colorado and the Great Lakes area,” Market said. “What really intrigues me is that thundersnow occurs here in the Midwest although the atmosphere isn’t affected by mountains or the Great Lakes.”

For the past 18 months, Market and his students have closely studied 39 cases of thundersnow from their archives, looking for patterns and working to improve their forecasting abilities.

Predicting where thundersnow will occur is difficult because a small band in the center of the storm tends to produce the greatest accumulation. One location might receive 12 to 20 inches of snow, while a location only 20 miles away may receive just three inches.

Verifying predictions is also difficult because cloud-to-cloud lightning accounts for 85 percent of lightning in a storm.

Reports of thundersnow are verified through a system of airport weather stations. Most airports have replaced human observers with automated weather stations that normally only detect cloud-to-ground lightning.

For thunder and lightning to happen, atmospheric conditions must be unstable. These conditions are much rarer in the winter than during the spring and summer. Researchers use measures of instability to help determine where a thunderstorm could occur.

One method they have found to be more accurate uses parameters for detecting thunderstorms in warmer seasons. During winter, these parameters are adjusted to reflect instability in one area relative to other areas.

“Our forecasting abilities have improved quite a bit between season one and two,” said Brian Pettegrew, a graduate research assistant. Season one, Pettegrew explained, refers to winter 2003-04, with season two referring to the current winter.

Though the NCAR team will be based in Columbia, it can expect to put some miles on the odometer.

“We may chase storms up to 12 hours away,” Pettegrew said. “We could go as far as South Dakota, Minnesota and Illinois.”

Once the scientists reach their destination, a box called a replicator will be launched with a large weather balloon into a thundersnow system. A motor inside the replicator turns a strip of 8 mm film that passes in front of an opening on the top of the box. As the film passes in front of the opening, it collects snow crystals and quickly dries.

Crystals form differently depending on the conditions within the system. By analyzing the shape of the crystals, the researchers will be able to determine how they form.

This, along with the other information gathered by the equipment, will be used to help define the characteristics of the system. It will also give them clues as to how the system forms and how it differs from other snowstorms that do not have thunder and lightning.


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