The National Weather Service issued a winter storm watch for all of Massachusetts on Thursday afternoon ahead of a system that could bring at least a half foot of snow to the region this weekend.

On Thursday at 2:39 p.m. a winter storm watch was issued by the National Weather Service valid from Saturday 7 p.m. until Sunday 4 p.m. for Franklin, Hampshire and Hampden counties.

A winter weather advisory is in effect in Massachusetts today as several inches of snow is expected to fall across the state, according to the National Weather Service's Boston office. Snow is already beginning in western Massachusetts as of 8 a.m. Thursday, and it will pick up in the eastern part of the state later this morning.