I am new on gardening living in Boston area, I am wondering if it is good time to overseed my grass before the snow coming.
It is really too late now to overseed. In a few very warm areas, and in a very warm winter, it might work but best wait til the soil warms up in the spring--not too early.
Sure -- you can overseed now. It's called dormant seeding, and it is discussed quite a bit over at the Lawn Care forum. The seed sits there all winter and sprouts nicely in the spring. The only reason I haven't done it that way is because then you can't use crabgrass preventer (or any germination inhibitor for weed seeds) in the springtime. But if you want to give it a try, you'll be happy with all the nice new grass sprouts you'll get in the spring. Keep it watered in the heat of the summer though, because it may struggle. I can recommend Rebel Elite TTT Fescue mix. I got it at Lowe's and I have been very happy with it.
Also if you like the idea of dormant seeding, head over to the Winter Sowing forum. You can sow nearly any kind of seed that way (perennials, annuals, vegetables, shrubs, trees, etc.), and there are hundreds of great gardeners over there who can help you get started. Basically you end up with dozens (or hundreds) of free plants. Dormant seeding is nothing new, and is a time-tested technique. (...contrary to some on the WS board who believe it was invented by one of the members there.) See you there, and good luck with your lawn.
I remembered one more thing about dormant seeding (for turf seeds). You need to wait until we are well into winter temperatures -- maybe even wait until Jan or Feb. You wouldn't want those seeds sprouting too soon during a warm spell.
Question from one who has never overseeded her lawn, and you can tell by looking: if we don't have snow cover, wouldn't you just be feeding the birds?