Major Winter Storm Bears Down on Eastern United States

— -- A major storm system that is expected to bring the Northeast its heaviest snowfall of the season began in earnest across the eastern United States early Thursday morning.

ABC News meteorologists tracking the storm predict it will likely dump snow from Washington, D.C., to New York by 7 a.m. Eastern time Thursday.

Winter storm warnings were in effect in Boston, Philadelphia, New York City and Portland, Maine, while blizzard warnings were in effect for eastern Long Island and eastern Massachusetts.

In preparation for the storm, public schools in Boston, New York City and Philadelphia announced Thursday closings.

At its peak, snow could fall as quickly as two to four inches per hour.

The National Weather Service urged people in the area to avoid traveling during the morning hours.

Travel conditions in the New York metro area are expected to deteriorate around daybreak on Thursday, possibly impacting the morning commute, according to the NWS.

To prepare for the storm, the New York City Department of Sanitation was pre-deploying 689 salt spreaders across the city, while a further 1600 snow plows were set to be activated once more than two inches of snow accumulated.

"As Mother Nature once again tests the resilience and strength of this state, I urge New Yorkers to plan ahead, stay informed, and above all, stay safe this weekend," New York Gov. Andrew M. Cuomo said on Wednesday. "I have directed state agencies to closely monitor conditions and to clear roadways as quickly as possible in order to avoid accidents and keep our roadways safe. I encourage everyone in the path of these storms to use extra caution and avoid unnecessary travel during these hazardous weather conditions."

The weather system could bring as much as a foot of snow to several major Northeast cities Thursday. While Philadelphia is predicted to get 4 to 6 inches of snow, New York City could see up to a foot and Boston could end up with as much as 15 inches, according to ABC News meteorologists.

The snowstorm will move from New York and arrive in eastern New England by 3:30 p.m. Eastern time on Thursday, according to ABC News meteorologists.

ABC News meteorologists predict the snowstorm will pass through Massachusetts and Maine before moving toward the Atlantic Ocean around 10 p.m. Eastern time Thursday.

Thursday's snowy conditions come just a day after some Northeastern cities saw record high temperatures in the 60s.

Another storm is taking aim at the West Coast as the region reels from this week’s already copious rainfall. The NWS has issued flood watches and warnings from Washington state to California.

“This storm is ready to strike,” ABC News senior meteorologist Max Golembo said.

ABC News meteorologists predict the storm will hit the Pacific Northwest on Thursday morning and will move into Northern and Central California later in the day, bringing more torrential rain to already saturated areas.

ABC News' Max Golembo contributed to this report.