CNN WIRE: Dangerous storms will bring significant flood risk to I-95 corridor

There is a dangerous risk for torrential rainfall and flash flooding in the mid-Atlantic and Northeast Thursday for millions along the Interstate 95 corridor. It could be another potentially serious flood event in a summer that’s been full of them.
CNN Weather via CNN Newsource

(CNN) — There is a dangerous risk for torrential rainfall and flash flooding in the mid-Atlantic and Northeast Thursday for millions along the Interstate 95 corridor. It could be another potentially serious flood event in a summer that’s been full of them.

Heavy storms are expected to bubble to life in the afternoon and last through the evening, and some could dump several inches of rain in a few hours, flooding roads and threatening public transit during the busy evening commute.

The Weather Prediction Center has issued a Level 3 of 4 risk for flooding rain from Washington, DC, to New York City and the southernmost part of Connecticut. This threat level means numerous flash floods are likely, some of which could threaten life and property in vulnerable urban areas. Philadelphia and Baltimore are also included in this risk area.

A Level 2 of 4 risk of flash flooding is in place for a broader area extending inland from Virginia Beach up through southern New England, including the rest of Connecticut.

Travel disruptions could be severe as the heaviest rain may fall during the evening commute. Drivers are urged to avoid flooded roadways and heed detours and closures. Subways could also see serious flooding, as New York saw earlier this month, when intense rainfall in the span of hours sent water gushing onto platforms and into subway cars.

Some storms are expected to train, or continue moving or redeveloping over the same areas, raising rainfall totals considerably. A few locations could get up to 8 inches of rain in a short amount of time, though exactly where the most intense storms will set up within the Level 3 of 4 area remains uncertain.

The rain is due to a cold front that is breaking a long-lasting, punishing heat dome that has been keeping the East sweltering during the day and simmering at night.

After a summer of frequent rain and flooding, the water simply has no place to go. And even if the region wasn’t soaked, extreme rainfall rates up to 3 inches per hour could overwhelm areas that typically drain well. Cities often struggle to handle heavy rain as pavement and asphalt keep water from soaking into the ground and instead head for drains that are prone to clogging or simply incapable of handling the volume of water.

“This type of setup carries the potential for very rapid rises on small streams and dangerous flooding in city streets,” the WPC said. “Residents in the mid‑Atlantic should ensure they have reliable ways to receive warnings throughout the day and into Thursday night.”

Flash floods are most common in summer, as warmer air can hold more moisture and intense daytime heat helps fuel potent storms. But overwhelming rainfall is becoming more prevalent due to climate change, as rising global temperatures drive weather toward extremes. Hourly rainfall rates have grown heavier in nearly 90% of large US cities since 1970, according to a study from the nonprofit research group Climate Central.

Rainfall across the mid-Atlantic and Northeast has already been above normal this summer — especially in parts of eastern Pennsylvania, central New Jersey, northern Maryland, and the DC suburbs — leaving soils saturated and primed for rapid runoff and flooding even without extreme amounts of rain.

Flood watches are already in effect for much of the region, including parts of Connecticut, all of New Jersey, southern New York, Washington, DC, Baltimore and eastern Pennsylvania. These watches will remain in place through Thursday evening.

Nearly all of New Jersey is in the risk area. The state has been slammed by flooding this summer, including when at least two people were killed two weeks ago. The increased risk also includes parts of Virginia that have flooded multiple times this season.

Flooding can be extremely dangerous at night, when it’s harder to see water covering roads. “If you encounter a flooded roadway, turn around and find another route,” the National Weather Service advises. “It only takes six inches of fast‑moving water to knock over an adult and just 12 inches to sweep away most vehicles.”

Less than two weeks ago, on July 19, the National Weather Service issued a flash flood emergency — the highest level of flood alert — for the Washington, DC, area with rainfall rates of 1 to 2 inches in 30 minutes raising rivers and sending water over roadways. Dozens of people had to be rescued from floodwaters after heavy rain struck parts of Virginia, Maryland and Washington, DC.

The flood risk shifts south into the Carolinas and part of Georgia on Friday, more states all too familiar with serious flooding this summer. Tropical Storm Chantal’s flooding rainfall killed at least one person in North Carolina in early July.