The region is already under a winter storm warning as a classic nor’easter builds over Boston and prepares to dump upwards of a foot of snow onto the roads, according to the National Weather Service.

NWS meteorologist Rob Megnia told the Herald that Boston and surrounding towns can expect to see the snow start to fall on very early Tuesday morning and continue through the evening commute. The snow will be heavy enough to make travel dangerous, he said.

“We certainly expect moderate to major impacts to travel,” Megnia said.

Weather Monday will be deceptively warm and temperate, according to the weather service, presenting a full work day to get prepared before the snow begins. High temperatures Monday could reach into the 50s under mostly sunny skies, Megnia said, but that all changes for Tuesday, when a 24-hour Winter Storm Warning goes into effect at 1 a.m.

“Most of tomorrow is going to be fine,” he said. “We won’t see the snow and precipitation move in until after midnight, and then it will intensify during the morning commute.”

The storm, according to the weather service’s warnings, will impact “portions of northern Connecticut, central, eastern, northeastern and western Massachusetts and northern Rhode Island.” Travel will be “difficult or impossible” during the periods of strongest snowfall, according to the warning.

With heavy bands of snow expected during both the morning and evening drives, Tuesday is an excellent day to consider working from home if possible, Megnia said.

The storm, a coastal weather pattern with winds from the north east, is a classic example of a nor’easter, Megnia said. It could leave upwards of a foot of snow over parts of Boston, with slightly less impact on the Cape and other coastal areas.

“Eight to 12 inches for the Boston metro area, probably a little bit lower the closer you get to the coast,” he said.

The snow should start to taper off by Tuesday night and end by Wednesday morning according to forecasting models, leaving behind days of cold.

“When those north-easterly winds start to kick in we’ll see temperatures drop,” he said. “When the storm departs, things are going to get really chilly.”

Daytime temperatures Wednesday and Thursday will be near freezing, but overnight lows will drop into the low 20s and upper teens. A predicted stiff breeze could push the wind-chill temperature into the single digits, Megnia said.

Seasonable cold weather will follow, according to the weather service, and Megnia said that the snow should stick around through at least the weekend.

Boston’s Victoria Chang feeds scratch grain to geese at Leverett Pond in Jamaica Plain. (Libby O’Neill/Boston Herald)