A snow emergency was announced today by Boston Mayor Martin Walsh, with up to two feet of snow forecast in a storm that is expected to last until Tuesday. Walsh said the amount of snow could be “unprecedented,” with up to two feet possible. The National Weather Service is calling it a “long duration snow event,” with heavy accumulations.

Snow is expected to start around 3 p.m. Boston Public Schools have already been cancelled for Monday and Tuesday. The storm is expect to affect areas from Boston, northward to Portland, Maine. Albany, New York is also expected to be within the zone receiving the greatest amount of snow.

A parking ban has been established in Boston on major arteries beginning at 4 p.m., with ticketing and towing starting at 6 p.m. Driving conditions are expected to be hazardous, with blowing and drifting snow causing difficult travel conditions. Only emergency operations city employees are asked to come to work on Monday. Logan International Airport is experiencing average flight delays of about two hours due to snow and ice.

Bill Cosby has cancelled a show scheduled for tonight at Boston’s Wilbur Theater, citing weather concerns. Protests outside the theater have not been cancelled.

The area is already struggling with several feet of snow already on the ground from previous storms. This is the third week in a row for a sizeable snowstorm.

Terry Eliasen, Meteorologist for WBZ-TV, says with light to moderate snow expected over a long period of time it might be the easiest of the recent storms to keep up with. The biggest problem will be where to put all the new snow. She says there is no relief from snow or cold in sight, with the possibility of “another significant snow storm” arriving Thursday or Friday, followed by some of the coldest temperatures in years.