The major storm sweeping ice, snow and sleet across the Eastern United States this weekend may also jolt the region with thunderclaps and lightning bolts.
This arresting winter phenomenon, known as “thundersnow,” occurs when thunder and lightning accompany heavy snowfall.
Here’s what to know about the unusual weather event:
What is thundersnow?
If you’re familiar with the mechanics of a thunderstorm, you’d be forgiven for wondering how “thundersnow” can even exist.
In a typical summertime thunderstorm, warm, moist air rises rapidly into the atmosphere, where it hardens into ice crystals, which then collide and cause a buildup of electrical charges. At a certain threshold, the electrical charges are released onto the earth’s surface in the form of lightning strikes.
But how can the process start when the air at ground level is cold enough for it to snow?
Very rarely, it turns out, are the conditions right for thundersnow. Occasionally, when air close to the ground is warmer than air higher in the atmosphere — though still cold enough that precipitation falls as snow — thundersnow can occur.
Thundersnow is rare, but it is more likely in a few settings, said Eric Guillot, the winter weather program manager for the National Weather Service. One of those is the Great Plains, where thunderstorms occur more often because of the frequent collision of warm, moist air with cool, dry air.
Thundersnow can also result when a storm moves over an area of warm, open water like the Great Lakes.
Mr. Guillot also said it can happen near mountains, when the air is forced upward because it has nowhere else to go, he said.
Very tall objects can also be associated with the phenomenon, said Dr. Sebastian Harkema, a thundersnow researcher. “Wind turbines, tall buildings, communication towers — those are initiation points that thundersnow tends to occur around,” he said. “And this is a result of the fact that the cloud pieces in these winter storms are relatively closer to the surface compared to summertime storms. Those tall objects are more likely to interact with the charge in the cloud.”
Thundersnow can be dangerous.
Thundersnow is no safer than a regular thunderstorm, Mr. Guillot said. “If you hear thunder, you’re close enough to be struck by lightning, so you probably shouldn’t be outside,” he said.
According to the Weather Service, during a severe thunderstorm — which it officially defines as a storm able to produce hail an inch or larger or wind gusts over 58 miles per hour — you should seek shelter indoors.
“Once inside, avoid contact with corded phones, electrical equipment, plumbing, and windows and doors. Finally, wait 30 minutes after the last lightning or thunder before going back outside,” the agency advises.
It’s also one of Mother Nature’s biggest marvels, at least for one meteorologist.
Witnessing thundersnow firsthand is a holy grail for some meteorologists. Most prominent among them may be Jim Cantore, of the Weather Channel, who says his enthusiasm for the phenomenon has been captured on television at least seven times.
In an interview, Mr. Cantore described what he loves about thundersnow. “I think when you think about a big snowstorm that stretches for hundreds of thousands of square miles, to be in the right place of where this very localized phenomena is — it’s kind of like the needle in the haystack. So to be in the place where the needle is in the haystack is the excitement. That’s the jolt,” he said.
“There’s a thrill to it. I think every meteorologist likes to get that moment. It’s like finding the pot of gold at the end of the rainbow, if you will, for meteorologists.”
Camille Baker is a Times reporter covering New York City and its surrounding areas.
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