Meteorologist Mark Overbeck has chased a lot of storms in Tornado Alley. And on Thursday, he saw an epic rotating supercell.
The only surprise? It was in Virginia.
Overbeck’s photos capture the flying-saucer-like storm whirling over the Blue Ridge Mountains east of Roanoke. Scattered thunderstorms, some severe, bubbled up along the Appalachian Mountains from Georgia to New York state on Thursday afternoon. But the one Overbeck tracked down was a little more special.
“Pretty much straight away I knew that this was the storm I was waiting for,” wrote Overbeck, who for days in advance had been monitoring the potential for an isolated rotating storm.
The storm formed in an environment characterized by strong wind shear. That means the winds changed speed and/or direction with height. The presence of wind shear is not all that unusual. But if you send a towering storm up to 35,000 feet into a significantly sheared environment, where different layers are subject to different winds, it could cause the storm to rotate.
Radar shows the somewhat shallow storm with well-pronounced rotation. A “hook echo,” a weather radar signature shaped like a hook, exists just east of Roanoke. In the second panel, the rotation — red against green — is prominently visible.
Overbeck captured his photos looking north, into the “vault” of the thunderstorm. On the left, the striated, rotating base of the storm can be seen. That’s the updraft, where air is spiraling inward and upward. To the right, a downdraft of rain-cooled air can be seen, accompanied by a torrential downpour and probably some hail. Looking at the downdraft, it’s tough not to whisper, “Swoosh.”
“On radar, the [storm’s signature] was relatively weak,” Overbeck said.
That’s not because it was a weak storm, however. On the contrary, “it indicates an extremely strong updraft that is suspending the precipitation within the storm, and not letting it fall,” he said.
That weak echo region can be seen on radar. Notice the hole to about 7,000 feet east of Roanoke. That’s the rotating updraft we see in Overbeck’s photos. It’s powerful enough that no rain falls. To the right, the downdraft of rain and hail — see that little purple blob? — is visible.
We can also examine winds in the storm using a vertical radar slice. Red and pink mark anything moving away from the radar. Green shows precipitation that is moving toward the radar. The juxtaposition of the two colors within the updraft is a clear indication of rotation.
At the top of the storm, you’ll notice the colors are quite bright, suggesting strong winds at 30,000 feet, blowing away from the radar at 30,000 feet. Those winds were howling up there Thursday, enough to carry cloud material associated with some of the storms in Virginia all the way up to New Jersey.
Most supercells that exhibit structure of this quality tend to be a bit taller; this one was only about 35,000 feet. But if we produce a 3-D rendering of the storm, we can easily see the counterclockwise-rotating updraft tower or “saucer cloud” that Overbeck was viewing.
Supercells, which are thunderstorms characterized by a persistent, rotating updraft, can form anywhere in the United States. They are most common across the Great Plains, though the storms have danced over cities such as Miami and Virginia Beach, and they have been witnessed in Massachusetts, Pennsylvania, Maine and just about everywhere in between. Seeing them this well-pronounced and with such classic structure is rare, however.
In this case, the storm did not produce a tornado, but it certainly tried.
Overbeck, who graduated from Virginia Tech in May with a degree in meteorology, was thrilled, he said on Twitter. “I wasn’t expecting it to be THIS impressive!”