Forecast Upped, Heaviest Snow to Fall 4-10 p.m.

Forecasters upped their prediction late Tuesday morning for Tuesday’s storm, now saying that 4-8 inches of snow will accumulate with snowfall rates up to an inch an hour at some points.

The National Weather Service changed its alert from a winter weather advisory to a winter storm warning just before 11 a.m. on Tuesday, saying that the snowfall will be "heavy at times" and quickly accumulate "making for hazardous driving conditions, especially for this evening’s commute."

Visibility will also decrease and drop as low as a quarter mile in the heavy snow.

The winter storm warning was put in place for the North Shore, plus all of northeast and central Massachusetts and southern New Hampshire. It runs until 1 a.m. on Wednesday, although most of the snow could fall in as little as a three hour window sometime between 4-10 p.m., the weather service said.

Light snow had started to fall in some areas of Massachusetts by 11 a.m., but the heaviest snow was not expected until after 4 p.m.

The winter storm warning was issued because an average of 6 inches or more of snow is expected in a 12 hour period.

"Travel will be slow at best on well-treated surfaces and quite difficult on any unplowed or untreated surfaces," the weather service warned.