by ETHAN SACKS

States along the Atlantic Coast and beyond were bracing for a major Nor'easter expected to pound the region in the coming days with damaging winds, heavy rain and snow and severe flooding.

Meteorologists warned that the storm — the result of a system moving east across the Midwest on Thursday that will collide with a coastal low-pressure system off the coast in the Atlantic — will cause damage from the Carolinas to Portland, Maine, through Friday and into Saturday. That collision is expected to lead to "bombogenesis," a cyclone effect that will strengthen the storm to dangerous levels as it moves north over open water.

"The reason this storm is particularly notable and particularly dangerous is that there are numerous impacts that will affect millions of people," NBC News meteorologist Sherri Pugh said.

"This isn't a forecast with a question of if these impacts are coming. It's how bad are they going to be," she said.

Winds were expected to gust up to 40 mph to 60 mph along the Northeast coast on Friday, hitting as high as 75 mph in Cape Cod, Massachusetts, stoking fears of power failures from downed trees.

Massachusetts Gov. Charlie Baker activated up to 200 members of the National Guard to work with state and local officials, saying at a news conference: "Some roads in downtown Boston and roads along the coast that usually have flooding issues will likely become impassable for some time."

Heavy rain of 1 to 4 inches was expected across parts of New Jersey; Long Island, New York; Connecticut; and Massachusetts. The deluge will cause coastal flooding at high tide in places like the Jersey Shore and the Massachusetts coast, as well as river and stream overflow farther inland. Pugh said up to 10 inches of snow was expected farther into the interior and in upstate New York.

For those least affected, Friday's will be a messy commute. For many others, however, it will be much, much worse.

The forecast was nearly as grim on the other side of the country, where a second powerful storm threatened much of the West. The National Weather Service advised of blanketing snow that will hit the Sierra Nevada mountains particularly hard and flash flooding along the California coast.

Santa Barbara County authorities ordered mandatory evacuations Thursday for residents in Montecito and other areas that were devastated by wildfires in December and deadly mudflow a month later. Twenty-one people died in Montecito on Jan. 9, when rains washed a torrent of mud and debris through the region.

"Due to the size and breadth of the evacuation area, we will not be able to notify everyone in person," Santa Barbara County Sheriff Bill Brown warned residents at a news conference hours before landfall, according to NBC Los Angeles. "Tell your neighbors, family members and friends. Do not wait for someone to contact you in person in order to leave.

"We just don't know how our watershed is going to react to this."