A graduation ceremony’s pomp and circumstance was rudely interrupted by a frightening, tornado-like cloud formation not far from Atlantic City and Philadelphia Thursday.
We know it wasn’t a tornado, but opinions vary widely on what kind of cloud it was that whipped onlookers into a frenzy at Absegami High School in the Galloway Township in southern New Jersey.
The Philadelphia Inquirer’s “Weather or Not” blog writes:
The National Weather Service in Mount Holly believes the mass probably was a “wall cloud,” as opposed to a funnel cloud or tornado.
It was a seriously dangerous storm, however, with 3/4-inch hail reported at 7 p.m. by a trained spotter. We don’t have a wind report from the scene, but at Atlantic City winds gusted to 24 m.p.h.
The video and more theories follow...
Video of storm uploaded to YouTube by MatthewRBlanchard
AccuWeather’s Henry Margusity theorizes:
I am sure it’s not a tornado or a funnel cloud, but I’m not 100% sure it’s not a wall cloud. What I don’t see in the video is any rotation. What I believe we are seeing is an updraft along the gust front that causes clouds to form in a shape that resembles a funnel.
Meteorologist Mike Masco of ABC2 in Philadelphia agrees with the non-rotating wall cloud theory:
The video clearly shows the families were witnessing what is called a wall cloud or pedestal cloud.
This type of cloud forms when the base of a storm cloud extends towards the surface of the ground. A wall cloud is in the area of the strongest updraft. If there was rotation, a tornado could likely have formed, but since there was no rotation in the storm, there was no chance for a tornado.
But Shawn Reynolds of the Weather Channel tweeted that Greg Forbes, TWC’s severe weather expert, said it looked like a cold air funnel.
CWG’s Ian Livingston, who just spent two weeks storm chasing in the Plains and blogged earlier today about identifying scary storm types, offers the following explanation:
Watching the video, and examining radar from the time of the storm, it appears the low-hanging cloud is a shelf cloud / outflow type feature with scud-type clouds associated with it. At times, the videographer pans up enough to see a “line” of similar low hanging clouds going up above their head (and presumably further). A rain curtain to the left, likely “behind” the low clouds, tends to back this up.
From 6:30-8:30 p.m., a line of intense storms developed and pushed into southeast New Jersey where the graduation was being held. The air mass was supportive of fairly low cloud bases due in part from the remnants of a large upper-level cold pool that had given the region spotty showers and stoms over recent days. Somewhat drier surface air than usual in storm situations may have also aided outflow features in a seemingly sub-severe storm.
Bottom line: sometimes identifying cloud forms isn’t clear cut.