Scary Cloud Was Not Tornadic, But People Were Right To Be Scared

Nora Kinney took this photo of a scary looking cloud
Friday evening during the severe weather. The National
Weather Service says this cloud was almost certainly
a downburst, a destruction rush of air crashing
downward from a thunderstor. 

After Friday's severe weather outbreak in Vermont and surrounding states, Nora Kinney shared on social media the photo you see in this post. It's an apocalyptic looking cloud as viewed from Essex looking toward Colchester as thunderstorms approached.

As you can see, it's pretty scary, this sort of bell shaped black thing appearing to lower toward the ground. Was it tornadic? After all, we were under a tornado watch at the time.

I wasn't 100 percent sure, so I put the question to the National Weather Service office in South Burlington. They got back to me right away with an answer. Nope. Nothing tornadic. But it something potentially dangerous.  

First that sort of bumpy cloud at the top of that cloud mass that appears to tilt upward to the left is a shelf cloud, which the NWS told me is "the leading edge of rain cooled air associated with thunderstorm outflow."

Shelf clouds are pretty common on the leading edge of thunderstorms, especially storms that are on the strong side, or severe.

That big dark thing that curves a bit outward like a bell is a downburst. You usually don't see them this well defined because they're often obscured by lighter rain out ahead of it.

A downburst is a very strong downdraft in a thunderstorm that can cause a lot of damage, which is why you should pretty much be as scared of a downdraft as you would be in a tornado. They're often mistaken for a tornado because people sometimes here that "freight train" sound as a downburst approahes.

A downburst usually causes wind damage in only a two mile area or so. They usually last 15 minutes or less, but can cause winds of up to 160 mph, and in rare cases even more than that. Downbursts are more common than tornadoes, probably happening ten times as frequently as tornadoes.

As I said, downburst are dangerous. When the National Weather Service thinks one will happen, they'll issue a severe thunderstorm warning. Downbursts are one reason why you should take a severe thunderstorm warning as seriously as a tornado warning. Severe thunderstorms can be very dangerous, too.

A severe thunderstorm warning from the National Weather Service in South Burlington was in effect when Kinney took the photo.

Pine tree against a house, and pine branches on the roof of this Shelburne,
Vermont house after Friday's destructive thunderstorm downburst there. 

The photo Kinney snapped probably happened at the same time a neighborhood in Colchester was being blasted by damaging winds.

The wind associated with this downburst was estimated at 80 mph. It took part of the roof off one home, knocked over quite a few trees, and sent a couch that had been sitting on a back deck flying, according to television station WPTZ.

And, typical of most downbursts, it was just one small area that was affected. Most of the rest of Colchester had little or no thunderstorm damage.

There was many downbursts with Friday's severe weather, which explains the widespread reports of damage. The destruction from the storms I talked about the other day in Shelburne was almost certainly caused by a downburst, for example.

So yeah, quite an interesting Friday evening in Vermont, from a weather, cloud and meterological standpoint.