What is thundersnow and how does it form? Explaining how a thunderstorm can produce snow

Doyle Rice
USA TODAY
  • Thundersnow is typically associated with very heavy rates of snow, which can lead to reduced visibility.
  • Thundersnow can be just as dangerous as a regular, rain-accompanied thunderstorm.
  • Thunder and lightning are much more common in warm-season thunderstorms.

Thundersnow – a thunderstorm that produces snow instead of rain – is sometimes reported during winter storms across the nation and in other countries.

Made famous by Weather Channel meteorologist Jim Cantore, whose excitement at hearing and seeing the phenomenon is legendary in several viral videos, including one from Chicago in 2011, thundersnow is still a relatively rare occurrence.

Thunder and lightning are much more common in warm-season storms because of convection, the upward motion of air that helps produce thunderstorms. It's fairly rare to have convection within a winter storm.

WHAT IS A BOMB CYCLONE?:Bomb cyclone is a winter hurricane. We explain.

SLEET VS. FREEZING RAIN:What's the difference between sleet, freezing rain and hail?

How does thundersnow occur?

What is thundersnow and how does it form? 

Thundersnow forms when temperature and moisture conditions are just right – a mass of cold on top of warm air, plus moist air closer to the ground.

As noted above, convection helps produce thunderstorms. It's unusual to have convection within a winter storm. Thunder and lightning are much more common in warm-season thunderstorms, according to meteorologist Jeff Haby of the WeatherPrediction.com.

When there's strong enough convection, along with plenty of moisture, a winter storm can produce thundersnow. 

During a winter storm, snowflakes and sleet pellets high in the clouds can collide. Those collisions create the same static charges as in a summer thunderstorm. With enough static charge, lightning is created.

Thundersnow is typically associated with very heavy rates of snow, which can lead to reduced visibility. Although the snow sometimes muffles the thunder, the lightning can be seen, said meteorologist Grant Gilmore, formerly of WFMY-TV in Greensboro, North Carolina.

One study found that when lightning strikes during a snowstorm, it's likely at least 6 inches of snow will fall.

Thundersnow is sometimes seen downstream of the Great Salt Lake and the Great Lakes during lake-effect snowstorms, according to the National Severe Storms Laboratory.

WHAT IS A NOR'EASTER?:Nor'easter storms can impact millions of people in the East with heavy snow, rain

WIND CHILL, EXPLAINED::What is wind chill? Understanding how the wind chill index is calculated

Thundersnow risks and dangers

Be careful out there: Thundersnow can be just as dangerous as a regular, rain-accompanied thunderstorm. 

"It's important to remember that when you hear thunder when it's snowing, the storm is producing lightning," said Jack Williams, the founding editor of USA TODAY's weather page in 1982. "Probably the last thing you'd think of are lightning safety rules – those are for summer ... but thunder always means there's lightning, and winter lightning is as dangerous as summer lightning."

Going outdoors in a snowstorm to watch for lightning can result in injury or death. Two men were struck by lightning during snowstorms in 1996 – one in Minnesota and the other in Colorado. In 2002, four teenagers in Maine were struck on a hill while sledding, according to the National Lightning Safety Institute.