OK, we've said it many times before: "The best time to overseed cool-season grasses (such as tall fescue and Kentucky bluegrass) is September." This is because the turf has more time to mature before crabgrass germination in the spring and the heat stress of summer. That being said, a chance of snow this weekend may provide an opportunity to cheat a little by getting some seed down that may actually do well this season. It's called Dormant seeding and it works best when there has been a light snowfall of generally less than an inch. 

Simply spread seed by hand on areas that need thickening up. As the snow melts it brings the seed into good contact with the soil where it will germinate as warmer spring temperatures arrive.  

Getting the timing right on seed starting is pretty important. Start too early and your plants will get leggy before it's time to put them outside. Start too late and you miss out on valuable growing time (especially if you want the first tomatoes on the block). Seeds are cheap, time is unrecoverable. Instead of starting all of your similar seeds (tomato for instance) at the same time, try starting 1/3 of them each week for three weeks. If warm weather is early, you'll be ahead. If cold weather lingers you'll still have seedlings at the appropriate transplant time.