Developing 'bomb cyclone' with atmospheric river to blast eastern US
A rapidly strengthening storm packed with a firehose of moisture will swing across the eastern United States through Wednesday night with areas of flooding rainfall, damaging winds and major travel disruptions.
Heavy rain and wind from D.C. to New England are on the way. AccuWeather’s Ali Reid is with AAA in Philadelphia where driving conditions will worsen throughout the day.
A storm will rapidly strengthen as it moves northward from the United States to Canada at midweek. The budding bomb cyclone will unleash torrential rain and powerful winds from the Appalachians to the Atlantic coast that can snarl travel, trigger flooding and cause power outages, AccuWeather meteorologists warn.
The beginnings of the storm already produced torrential downpours and prompted tornado warnings in parts of the southeastern United States on Monday and Tuesday.
Heavy rain led to flash flooding in Mandeville, Louisiana, on Dec. 9, leaving streets covered with water.
As downpours and thunderstorms ramped up in the Southeast on Tuesday night, rain began to expand northward and soak the central Appalachians, mid-Atlantic and southern New England regions.
The storm will quickly reorganize along the upper mid-Atlantic coast Wednesday and intensify. The central pressure of the storm will plunge, creating a giant vacuum in the atmosphere that will cause winds to rush in toward the middle of the storm. When the central pressure crashes 0.71 of an inch of mercury (24 millibars) in 24 hours or less, like this storm is projected to do, bombogenesis will occur and a bomb cyclone will be born.
This radar image was captured on Wednesday afternoon Dec. 11, 2024. Rain intensity is depicted as green (light) and heavy (yellow, orange and red). Snow is displayed in blue. (AccuWeather)
Torrential rain and strong winds will target the Interstate 95 corridor with major travel delays from into Wednesday night.
"Some rain will act like a giant firehose and organize into an intense north-to-south, west-to-east crawling squall with gusty winds," AccuWeather Chief On-Air Meteorologist Bernie Rayno said.
Enough rain will fall--a general 1 to 4 inches-- to boost stream, river, lake and reservoir levels and trigger urban flooding. The AccuWeather Local StormMax™ rainfall for this storm is 6 inches in the Southeast and 8 inches in the Northeast.
GET THE FREE ACCUWEATHER APP
•Have the app? Unlock AccuWeather Alerts™ with Premium+
A plume of moisture will likely be traced for more than 2,000 miles--all the way from the northeastern U.S. to the Caribbean Sea and will "fit the definition of an atmospheric river," Rayno added.
This advancing squall will bring the highest risk of accidents on the roads, and ground stops at some airports. Ponding, greatly reduced visibility and even thunder and lightning can accompany the squall along the Interstate 95 corridor. Fog alone has already been causing delays in some locations and will resume or continue until the storm departs Wednesday night.
"Locally severe thunderstorms can occur into Wednesday evening in the coastal Northeast with the possibility of a few tornadoes in part of the mid-Atlantic," Rayno added. The tornadoes would be brief but potentially rain-wrapped and difficult to see.
While much of the heavy rain will fall east of areas that received multiple feet of snow in recent weeks around the Great Lakes, some downpours will reach northern New England.
"The risk for significant flooding will be further amplified across the higher elevations of Vermont, New Hampshire and Maine where there is a considerable snowpack of several inches on the ground. Rapidly melting snow can add another 1 to 2 inches of liquid water to the runoff and especially in areas of steep terrain, rapidly rising water can lead to life-threatening flooding," AccuWeather Chief Meteorologist Jonathan Porter said.
Rain can also significantly increase the load on roofs that have not been cleared of snow. This added weight could lead to roof failure on flat or shallow-angle gables.
Even without snow on the ground, the firehose effect of rain alone can lead to significant urban and small stream flooding from Delmarva to New England, including the major metro areas of Philadelphia, New York City, Boston, Providence, Rhode Island, and Hartford, Connecticut. Driving through flooded roads may not only ruin vehicles, but could be serious enough to be a life-threatening situation.
Powerful wind gusts can occur without any thunder and lightning from this storm. The strongest winds will be from the south along the Atlantic coast into Wednesday night. In this zone from eastern North Carolina to southeastern Maine and the Maritime Provinces of Canada, gusts will frequently range between 50 and 70 mph with an AccuWeather Local StormMax™ gust of 85 mph.
Farther west, winds may be light most of the time over the central Appalachians Wednesday. However, as the storm center moves toward Canada and bombs out, strong winds from the west and northwest will range from 30-50 mph with locally higher gusts. These same gusts will break through to the Atlantic Seaboard later Wednesday night and Thursday.
While sporadic power outages can occur as the storm strengthens in the Midwest and the Northeast, the greatest risk of regional problems, including damage to property and holiday decorations, will be in coastal areas of the Northeast and in eastern New England in particular.
The impactful nature of the storm in coastal areas of the Northeast will be like a landfilling strong tropical storm or hurricane.
People are urged to secure holiday decorations as well as trash cans, recycling bins, tarps and trampolines so they do not become airborne projectiles that can injure people or damage property.
In the wake of the storm, Arctic air will rush in from the Midwest and can catch up to the back side of the storm's moisture.
Aside from a period of heavy lake-effect snow from Wednesday night to Friday, a general burst of snow can quickly cover roads and make for slippery driving from the eastern part of the Ohio and Tennessee valleys to the Appalachians from Wednesday to early Thursday. Click here for more information on the Arctic air and snow that follows the storm.
Want next-level safety, ad-free? Unlock advanced, hyperlocal severe weather alerts when you subscribe to Premium+ on the AccuWeather app. AccuWeather Alerts™ are prompted by our expert meteorologists who monitor and analyze dangerous weather risks 24/7 to keep you and your family safer.
Report a Typo
