Tuesday afternoon featured filtered sunshine across most of the D.C. area. Then, toward the evening, a pair of waterspouts spun up over the Chesapeake Bay.
Kristina Peters snapped this photo Tuesday evening of the funnels near Deale, about 20 miles south of Annapolis. “We’ve lived here 10 years and I can’t recall seeing anything like it,” Peters said via email.
At least two waterspouts can be seen in the picture, which Peters saw looking east over the Chesapeake just before 7 p.m. The most visually impressive waterspout looms at the center of the image, with a more subtle funnel on the far left. A bush of spray can be seen on the water below and just to the right of the condensation funnel, linking the appendage to the surface.
Additional waterspouts were reported nearby. About 20 minutes after Peters’s sighting, a boater reported a waterspout east of Mayo, southeast of Annapolis.
While out of the ordinary, waterspouts over the Chesapeake are not rare. “We get a few each season during late July, August and into September,” said Dan Hofmann, a meteorologist at the National Weather Service in Sterling.
Tuesday’s setup featured a trough of low pressure — accompanied by a dip in the jet stream — in the upper levels of the atmosphere. That allowed sufficiently cool air aloft to spill into the Mid-Atlantic. This cool air mass was located “between 10 and 25,000 feet up,” according to Hofmann. “That can help you get a lot of rising air near the surface.”
Water temperatures across the Chesapeake are running in the low to mid-80s. The contrast against the chilly air a few miles above the ground means that any shower or thunderstorm updrafts could get a boost.
“That can be enough to vertically stretch any weak surface whirls into a waterspout,” Hofmann said.
In Tuesday’s episode, a shallow, low-topped shower — about 18,000 feet tall — parked itself along a narrow zone of converging winds over the Chesapeake.
Meanwhile, an expansive area of moderate rain was draped farther to the east, which may have played a key role in forming these funnels. The cool air exiting this large rain shield may have interacted with subtle boundaries over the Chesapeake, creating scores of invisible tiny whirls. These are similar to the dozens of tiny whirlpools your body makes when you swim in a pool.
But when such an eddy passes beneath a growing cloud, it can be tilted vertically and grow in size, as Hofmann explained.
Additional “cold air funnels” were reported Tuesday in coastal Delaware, New Jersey and even New York City.
Don’t expect a repeat event Wednesday, Hofmann said.
“Today’s environment won’t be quite as favorable for waterspouts, but it’s certainly not out of the question,” he said.