How does the rare phenomenon thundersnow occur?

By Chaffin Mitchell, AccuWeather staff writer

Booming claps of thunder following flashes of lightning are a rare but awe-inspiring occurrence that can accompany intense snowfall - a phenomenon called thundersnow.

The process for thundersnow is a very similar to the process for the typical summertime thunderstorm; however, the top of the cumulonimbus cloud resulting in thundersnow is usually quite low. Moist air is lifted and rapidly rises due to instability in the atmosphere.

"In the case for nor'easters during the winter, an area of low pressure rapidly develops at the surface near the coast which leads to a large amount of rising air with plenty of moisture from the ocean," AccuWeather Meteorologist Jordan Root said.

Air then rapidly accelerates upwards due to cold air layered over warmer air, which causes instability. Root said the rising air leads to the formation of snow, ice and little balls of snow which crash into each other as they are lifted.

"This causes charges to be exchanged and moved around, leading to an electrified cloud. Faster rising air will create more snow and ice which will crash into each other more violently, leading to the greater chance for lightning and thunder," Root said.

According to Root, it takes several ingredients to come together at the right time during the winter for thundersnow to occur, which makes it rare.

"Thunderstorms during the warm season have a much easier time developing strong updrafts because there is more warmth and moisture to feed on and more instability aloft," Root said.

During the winter, there isn't enough warm air to create an updraft so it takes a much more dynamic system, such as a nor'easter or a bomb cyclone, to send air rapidly upwards.

"In the United States, thundersnow occurs more often in the central part of the country, Intermountain West and across the Great Lakes region. Intense lake-effect snow bands, which have pockets of rapidly rising air due to the sharp contrast between cold air aloft and the warm lake water, often produce thundersnow. Meanwhile, mountains across the West help air to rise quickly which can lead to thundersnow," Root said.

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Thundersnow is often accompanied by intense rates of snowfall, usually several inches per hour, that lead to dangerously low visibility. It is an indication that a storm is rapidly strengthening.

NY nor'easter March 2018

Pedestrians walk along Delancey St. during a snowstorm, Wednesday, March 7, 2018, in New York. The New York metro area was hit with another winter storm Wednesday just days after another nor'easter hammered the region with high winds. (AP Photo/Mary Altaffer)

"One of the bigger differences between thunder during the warm season and thunder during a snowstorm is the distance at which it can be heard," Root said.

Since the thunder occurs when snow is falling, the snow tends to muffle the sound, limiting the distance at which it can be heard.

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