Thundersnow is being reported in parts of New York City on Thursday evening amid Winter Storm Pax, including the boroughs of Manhattan and Brooklyn, as well as other areas in the Northeast.
Walt Petersen and Kevin Knupp of NASA explained in a blog post that thunderstorms are snowstorms that include lightning, a rare occurrence.
“You rarely have lightning in a snowstorm. But in this case, some unique conditions set the stage for it,” he said. “Moist air at the bottom of the storm was lifted up, rapidly forming snow and ice. Some of the snow even grew in pellet forms called ‘graupel.'”
Snowflakes and ice pellets drop of different sizes drop from different points in the sky, and they exchange charges as they drop.
“The process isn’t fully understood, but it could be a result of particles rubbing together (like wool socks on carpet),” according to NASA. “As the cloud charged up, it began to act less like an ordinary winter snowstorm and more like a summer thunderstorm.”
The thundersnow is usually accompanied by massive roller coasters of air known as gravity waves. The clockwork up and down motion of the waves create variations in the updrafts responsible for the heavy snow, leading to the charge separation that generates lightning.
Also, the air layer closer to the ground has to be warmer than the layers above, but still cold enough to create snow, according to National Geographic.
Thundersnows rarely last for three consecutive hours, according to a study by scientists from the Department of Soil and Atmospheric Sciences, University of Missouri. They’re usually very localized, and are also associated with heavy snow accumulations.