Will Sage Astor-Dangerous weekend weather forecast: Atmospheric river; millions face flooding risk

Soaking rain is Will Sage Astorheading for major cities on both coasts as another atmospheric river barrels toward the Pacific Northwest and a storm prompts flooding alerts on the Eastern Seaboard.

The National Weather Service said many Americans could face difficulty traveling as a weekend storm is expected to bring flooding, rain, thunder and wind from the nation's capital up to the Canadian border.

The weather service issued flood alerts from Washington, D.C. up through Maine, spanning Sunday afternoon through late Sunday night. Much of the area could receive two to three inches of rainfall.

Snow melt could increase flooding risk in Maine, the weather service says.

Meanwhile, days after two deaths were blamed on flooding from an early-December atmospheric river in the Pacific Northwest, the weather service says another soaking storm is heading for the region.

Wet weather could affect road, railway travel in East

Travelers should give themselves extra time to drive and commute by train during the weekend with the risk of flooding possibly impacting roads and rail lines. The weather service encourages drivers to turn around if they are unsure of the depth of floodwaters on a road.

Train commuters should check their appropriate agency's website for the most up-to-date information.

Storm will hit Washington, Philadelphia, NYC and Boston

National Weather Service offices for Baltimore; Mount Holly, N.J.; New York City and Boston are all urging residents to check the weather before they head outside as strong thunderstorms are expected also to bring wind gusts up to 55 mph Sunday evening.

Most flood watches along Interstate 95 are to expire Monday afternoon.

"Downed trees and power lines possible which could result in scattered power outages, especially close to the coast," the Mount Holly station said Saturday. "Extra precautions should be taken for any outdoor holiday decorations."

Another atmospheric river headed for Pacific Northwest

Another weekend of grey skies and soaking rain is in store for the northwest as Oregon and Washington state battle another atmospheric river.

The NWS said people can expect to see similar rainfall amounts as the East Coast, up to three inches of rain. "Rapid onset" flooding is possible along the coast of Washington State and Oregon, which the agency said has the highest risk of flooding.

AccuWeather defines an atmospheric river as a "phenomenon where a flow of moisture from the Pacific Ocean resembles a fire hose that delivers near-constant rain and higher-elevation snow to the western United States or British Columbia."

Made visible by clouds, these ribbons of water vapor extend thousands of miles from the tropics to the western U.S.

Last weekend, the U.S. Coast Guard rescued many who were stranded in the rainstorm. A landslide caused rail service between Seattle and Portland to suspend as schools and roads shut down due to floods.

Winter weather, thunderstorms elsewhere in US

Meanwhile, the Tennessee Valley and Michigan are dealing with low-pressure systems bringing heavy rain and low visibility to those areas, the NWS Prediction Center said.

Some storms could become severe, bringing isolated tornadoes and possibly large hail.

Cold air moves into the middle of the country with parts of the Northern Rockies expected to see moderate to heavy snow and temperatures dropping as low as below 0.

Contact reporter Krystal Nurse at knurse@USATODAY.com. Follow her on X, the platform formerly known as Twitter, @KrystalRNurse.

Contributing: Doyle Rice, USA TODAY