Rare 'thundersnow' is hitting New York -- here's what that is and why it happens

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  • Snowfall rates were picking up for the storm hitting the Northeast on Wednesday.
  • The National Weather Service said there may be “thundersnow,” a rare meteorological phenomenon in which a storm involving thunder and lightning also drops snow.
  • Not long after noon ET, it happened.
  • That’s rare because the storms that drop snow are usually different from the storms that cause thunder and lightning.

While dropping snow and rain throughout the Northeast, the second nor’easter to strike in March also produced the rare event known as “thundersnow.”

The New York office of the National Weather Service had announced earlier Wednesday morning that the region may see the uncommon meteorological phenomenon later in the day.

“During the time of the heaviest snowfall this afternoon, thundersnow is a possibility,” NWS New York said on Twitter. “Snowfall rates of 1-2” per hour, with locally higher rates (2”+per hour) are also possible primarily after noon within the heaviest snow bands.”

New Yorkers got to experience the thundersnow’s start shortly after noon ET.

The term thundersnow describes a storm with thunder and lightning that also drops snow. Such events are rare because the storms that drop snow are usually very different from the storms that cause thunder and lightning.

As Greg Forbes, an expert in severe weather, explained for The Weather Channel, normal thunderstorms tend to be tall, narrow storms with quickly rising air. Snowstorms are usually marked by large, extensive, shallow, and flat clouds with gentle upward and downward motion.

When a snowstorm develops a more intense upward lift of air, that can lead to thundersnow. The phenomenon is most common in places where geographical features like lakes or mountains create turbulence that can lead to unstable weather systems, which in turn force “turrets” of clouds to rise upward.

High enough up in the atmosphere in those cloud turrets, cold temperatures can mean that both snowflakes and small hailstones form at the same time, according to Forbes. The interaction between snow and hail particles can create electrical charges. At a large enough scale, you start to get lightning – and the thunder that follows it.

In such situations, you also get a lot of snow forming very quickly, which can lead to lots of accumulation.

Thundersnow is more common in lake-effect storms, which is why it’s seen more frequently around the Great Lakes. But it can also happen in extratropical cyclones (which are swirling storms outside tropics, like nor’easters).

Thundersnow or not, it looks as if accumulation rates are picking up for this storm. Stay dry and stay warm.

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