Every winter, when a big snowstorm looms, one question frequently pops up: Could we get thundersnow?
Thundersnow is exactly what it sounds like: thunder and lightning occurring during a snowstorm instead of a rainstorm.
Most snow falls from fairly gentle, layered clouds. Thunderstorms, by contrast, require strong upward motion or air rising rapidly to build tall clouds that generate lightning.
How thundersnow happens
For thundersnow to occur, a winter storm needs to tap into intense upward motion, similar to what you’d find in a summer thunderstorm. This usually happens in powerful coastal storms, often Nor’easters, where:
- Warm, moist air surges northward.
- Cold air is entrenched at the surface.
- Strong lift develops along fronts or within heavy snow bands.
Inside these intense snow bands, air rises rapidly. That vertical motion allows ice crystals to collide, creating electrical charge separation, the same basic process that produces lightning in warm-season storms.
When lightning flashes inside a snow band, you get thunder — though it often sounds different. Snow absorbs sound more efficiently than rain, so thunder during a snowstorm can sound muted, distant or muffled. Sometimes it’s a deep rumble. Other times it’s like a sudden clap.
Why it’s rare
Thundersnow requires an overlap of ingredients:
- Heavy precipitation
- Strong lift
- Instability in the atmosphere
- Sufficient moisture
Most winter storms simply don’t have enough instability. There is a special type of instability that can develop, however, where the air is unstable to both vertical and horizontal motions, creating a kind of diagonal, or slantwise ascent.
Thundersnow tends to be confined to the most intense part of a storm, often where snowfall rates exceed 2 inches per hour. Coastal storms that intensify rapidly are particularly likely to develop pockets of thundersnow.
When you see thundersnow, it’s usually a sign the storm is near peak intensity.
Thundersnow in DC
We’ve seen it in the DC area during several high-end snowstorms.
There were reports during parts of the January 2016 blizzard, Snowzilla, particularly as heavy snow bands pivoted across the region. It was also observed in a heavy wet snowstorm in 2006 and during the surprise Veterans Day snowstorm in 1987.
When thundersnow strikes, you can count on The Weather Channel’s Jim Cantore reacting with enthusiasm. He’s become something of a folk hero for celebrating it live on air.
