A winter storm watch remains in effect for York and Cumberland counties for a system that is expected to deliver the Portland area’s first significant snowfall of the season in two waves starting late Sunday.

The storm’s exact timing and total snowfall remained uncertain as of Saturday night, but a National Weather Service meteorologist said the storm is expected to reach Portland by late Sunday evening. Snow will fall Sunday night and is expected to turn into a wintry mix early Monday and then taper off during the day before intensifying again Monday night through early Tuesday.

Estimated snowfall for most of York and Cumberland counties, including Portland, is 1 to 2 inches on Sunday, followed by another 3 to 4 inches Monday, for a total of 4 to 6 inches, said National Weather Service meteorologist William Watson.

“It wouldn’t surprise me if it was maybe a little more than that,” Watson said. “Basically, it’s coming in two rounds.”

Rockland and Belfast are expected to receive 6-8 inches of snow over the two-day period.

Central Maine Power Co. said Saturday that it was closely monitoring weather forecasts and preparing to respond to potential power outages that could occur as a result of the snowstorm.

The storm system follows one that arrived Wednesday night, bringing high winds and power outages to thousands of homes and up to a foot of snow in northern Maine.