“This definitely has the potential to be the most intense thunderstorm outbreak of this year,” he said.
While the worst of the storms are projected for midmorning through late afternoon, the exact timing and nature of Thursday’s storms could dictate the severity of the impact, Samenow said.
Storms should not be as intense if they hit early in the day, but conditions could turn out to “be more explosive” if they arrive later, he said. That could include destructive winds and even a few tornadoes.
Across the region, transportation agencies prepared Wednesday to deal with the looming storm.
The D.C. Department of Transportation planned to have generators available to power any dark traffic signals.
In Virginia, hundreds of maintenance workers were to be standing by in case of downed wires, fallen trees or dark traffic signals.
Crews in Maryland readied chain saws and other equipment Wednesday as they awaited the storm.
“Thunderstorms and summer weather is almost all reactive,” said David Buck, a spokesman for the Maryland State Highway Administration.
Pepco was gearing up “for a significant storm,” said Myra Oppel, a company spokeswoman. As soon as crews are able to work safely, they will be out repairing any outages, she said.
“If we were expecting landfall from a hurricane, we could have a better sense in terms of what to expect in terms of outages,” Oppel said. “This, we know there’s a severe thunderstorm, but it depends on how it moves in and how it manifests itself in terms of wind speeds and how heavy the rain is.”
Flash flooding was a key concern after heavy rain in recent weeks.
“We’re forecasting heavy rainfall, and with the recent bout of rain the D.C. metro area has received, we really can’t take too much more rainfall of any kind without seeing flash flooding,” said Howard Silverman, senior meteorologist at the National Weather Service’s Baltimore-Washington forecast office.
Flooding could be particularly dangerous for drivers who may not know they commute through flood-prone areas, Buck said.
Officials urged travelers not to drive through standing water and to treat intersections without power as four-way stops. They also said not to touch downed trees, because they could be tangled up with downed power wires.
Gusting winds and pounding rain could also snarl air travel, with delayed flights in other cities potentially creating headaches throughout the aviation system.
“If other major airport hubs are affected, those impacts could cascade through the system,” said Rob Yingling, a spokesman for the Metropolitan Washington Airports Authority, which operates Reagan National and Dulles International airports. “Chicago or New York, if there’s major cancellations there, that could have a cascading effect on some of the flights here.”
These storms are coming a year after
a destructive derecho
swept through the area. But while “a derecho-type event” is not out of the question, this will most likely be just severe thunderstorms, Samenow said.