By TIM ALEXANDER
Illinois Correspondent

URBANA, Ill. — It’s a weather event so rare that even weather professionals have a hard time explaining it. And it showed its muted fury on several occasions during the great “Groundhog Day Blizzard of 2011” throughout the central Illinois area: Thundersnow.

First scientifically studied and charted by the Chinese as far back as 250 B.C., the rare phenomenon of thunder and lightning in the midst of a winter blizzard must have inspired in the ancients a frantic sense of impending doom, intermingled with rapturous awe. According to a leading weather expert in Illinois, things really haven’t changed much in that respect.

“Once you’ve seen and heard (thundersnow), it sticks with you,” said Jim Angel, state climatologist with the Illinois State Water Survey. “It gets your attention. You aren’t expecting it, and it contains a different kind of sound for thunder and a different kind of light for the lightning. It’s a very memorable experience.”

Angel said unlike the loud booms of thunder and brilliant, cloud-to-ground lightning strikes that typically accompany a summer thunderstorm, thundersnow’s roar is usually more muffled and its lightning more diffused.
“It’s not as common to see lightning bolts hitting the ground; it’s more of a strobe-like effect or just a flash in the clouds,” he explained. “Usually, from what I’ve experienced, (the lightning) seems to have more of a yellowish tint to it.”

According to the National Weather Service (NWS) in Chicago, more than 60 lightning events were recorded in central and northern Illinois during the height of the region’s thundersnow activity on the evening of Feb. 1 – though none of the several thundersnow instances to occur in the Peoria area were reflected on NWS’ data map.

Many were clustered in the Ottawa, Streator and Morris areas along Interstate 80, accompanied by winds gusting upwards of 60 miles per hour, according to Chicago NWS.

Blowing snow ranging from 15 inches in accumulation in Peoria to 20.2 inches at O’Hare Airport in Chicago carried the thunder and lightning across the upper portion of the state.

According to Angel, the weather dynamics that allow thundersnow to occur are similar to those accompanying normal spring and summer thunderstorms.
“But it’s much colder, so what falls is snow and not rain. It’s usually kicked off by strong low pressure systems rolling through. You have a lot of upper motion in the air that builds up into clouds and precipitates the snow. It’s so large and vigorous it sets off lightning,” Angel said.

Stephen Rodriquez, a meteorologist with the Chicago NWS, delved a little deeper in his written explanation and summary of the event: “For the development of springtime thunderstorms, several components are needed: lift or forcing, moisture and instability. These components can also be discussed with winter time lightning.” He added that all three components – most notably instability – were present during the 2011 blizzard.

Writes meteorologist Jeff Haby for www.theweatherprediction.com (described as the ultimate weather education website): “It is the convective process that creates the favorable charge separation for lightning to occur. It is fairly rare to have convection within a temperature sounding that can support snow ... Two mechanisms are important to the creation of thundersnow, and they are elevated instability and strong dynamic lifting. Each of these mechanisms reinforces the other.”

Take what you can from those respective summaries of the causes of thundersnow, but one thing nearly all weather experts agree on is that it is an infrequent, sometimes alarming and always, without question, breathtaking event to behold.

“It’s very rare, and rather surprising to experience in person,” Angel said. “I have personally seen it only two or three times in my lifetime. It’s something that normally happens only once every 10 or 20 years in the same spot.
“I first experienced it in the 1980s driving over to Indianapolis in a blinding snowstorm. You hear a rumble, see a flash of lightning and think, ‘no – that can’t be.’”

Though central Illinois and the Midwest have experienced thundersnow at least a couple of times this century, it is so unusual that the NWS recorded only 378 instances of the phenomenon in the period spanning 1961-90.

More recent research shows that conditions for thundersnow can be found in many heavy-producing snowstorms such as the one- to four-inch-per-hour variety that swept through the Peoria area in early February. Almost 90 percent of thundersnow instances recently recorded have occurred during snowfalls of more than four inches, researchers have found.

Though most lightning produced by thundersnow is contained within the cloud structure, a few strikes in western Tazewell and Woodford  counties near the Illinois River on the evening of Feb. 1 appeared to reach ground. This was much like normal lightning, Angel concluded, though with perhaps even more potential for destruction.

“I have never heard of injuries or damage (from thundersnow lightning strikes), but that doesn’t mean it hasn’t happened,” he said. “With the amount of energy we’re talking about, with a cloud-to-ground hit, it could cause tremendous damage.”

Jeff Koch, farm loans chief for the Illinois state office of the USDA’s Farm Services Agency (FSA), said as of last Friday no Illinois farmers had applied for emergency relief to cover livestock, feed or other losses resulting from the blizzard, even though the USDA announced on Feb. 4 that disaster assistance was available for livestock producers affected by ice, cold and heavy snowfall.
The executive director for the FSA Tazewell County office in central Illinois, however, said one producer contacted his office with an unusual request for assistance in the wake of the blizzard.

“My first request came (Feb. 11) in regards to livestock feed,” Guy Mattson said. “The producer was inquiring as to whether or not he would be eligible to receive any benefits for having to feed extra hay and corn to his cows. I told him I’m not sure of the procedure on that or whether he would be eligible; I have some questions into the state office now because I couldn’t give him a good, solid answer.

“I kind of understand what he’s saying. I know he’s a small cattle producer, and I’m going to be looking into it.”

Pat Slattery, public affairs specialist for the NWS’ central region office in Kansas City, said thundersnow springing from a blizzard is not such a rare event and that hundreds of instances could have occurred during the massive blizzard of 2011.

“Along with central Illinois, I believe there (was thundersnow) in Missouri, Kansas and other states in the Midwest,” he said. “These storms also covered Southern regions as well, leading to the possibility of thundersnow events.”