When the soil, not the air, temperature falls below that which the seeds need to germinate. Frosts and freezing air temperatures will, eventually lower the soil temperatures but that happens fairly slowly. That is in the 45 to 65 degree range depending on which grass seed is used. Blue Grass needs warmer soil temperatures then does Perennial Rye.

Generally speaking, it is too late for much success this season. Even in my very mild climate, the middle of October is typically considered the cut-off point (and we are yet to experience nighttime temperatures below the mid 40's). Sometimes, later seeding will offer germination but the rate is poor and the germination very slow. Often the seed will rot in the winter rains and snow before it is able to germinates.

Ohio State University says if seeding cannot be done by October 30 it should be delayed to next spring. But then they also say that one can winter seed and those seeds would stay dormant until the proper growing time in the spring and they will not rot.

Here is a link that might be useful: Fall grass seeding

Thanks! I will overseed very soon as I feel that spring seeding has been a waste of money in the past.