JOHNSON COUNTY, Ind. – Wednesday’s winter storm provided some Hoosiers with a rare weather phenomenon called “thundersnow.”

Viewers in the Trafalgar area reported hearing thunder and seeing lightning while snow was falling. The National Weather Service confirmed the phenomenon in Johnson and Brown counties. Additional reports came in from Elwood in Madison County, Portland in Jay County and Hartford City in Blackford County later in the morning.

The NWS described the occurrence as “something unusual,” with lightning sensors picking up thundersnow in the area.

We typically associate thunder and lightning with thunderstorms accompanied by rain. Under certain conditions, however, snow can actually accompany a thunderstorm.

According to the National Oceanic and Atmospheric Administration (NOAA), thundersnow can occur when there is strong instability combined with abundant moisture above the Earth’s surface—such as a warm front.

NOAA said the conditions for thundersnow are similar to what happens during a typical thunderstorm. It’s rarer for this to happen with snow, however, because temperatures tend to be colder when snow falls, both at higher and lower points of the atmosphere.

“However, in some winter storms, shallow layers of warm air are lifted and continue to rise on their own – increasing snowfall and causing enough electric charge separation for lightning to occur,” the agency said.

The result: lightning and thunder accompanied by snow. NOAA also noted that thundersnow is typically associated with increased snowfall amounts.