Snow was falling in the Mid-Atlantic and New York City on Sunday. The coldest air in several years will descend across much of the country starting Monday, forecasters said.

Over 135 million people across 35 states will be under cold weather alerts over the next several days as the mid-Atlantic and Northeast ready for another round of rain and snow, driven by a low-pressure system developing off the coast of the Carolinas.

Storm Demi is forecast to bring snow to some of the nation’s largest cities, including Washington D.C., New York, and Boston, on Sunday. The winter storm will also usher in cold temperatures in its wake.

Most of the United States is being assailed with extreme winter weather this week as Arctic air blasts south from Canada, snow tracks up the Northeast coast and a potentially crippling winter storm takes aim at the South.

While it's not clear what impact a mix of rain, freezing rain, sleet and snow may have on the capital city, officials say now is the time to begin preparations.