Maybe. Zone 5 doesn't tell us when your first frost is, or how cold it is now. Zone 5 only tells us the coldest that it gets in the winter.

Where are you? What are your current daily highs and lows? What is your average first frost date?

I'm in central MA, and the highs right now are around 75 degrees and lows are about 55. I found one site that indicated that the average first frost takes place around 10/17 in Worcester, MA.

I think you've missed the window to do a fall seeding. If you seed now, the seed may germinate but not get established before the frost hits.

You can wait a few more weeks until it is too cold for the seeds to germinate, and seed then. The seed will sit there and the snow will pull some down into the ground as it melts. Then in the spring when it gets warm enough, the seed will germinate. You may lose some seed to birds and insects or to premature germination, but you'll probably have better results than if you try to seed now or try a spring seeding. If you dormant seed, the seed will germinate sooner than with a spring seeding, so it'll have more time to establish before the heat of the summer.

Thanks, bpgreen. Will I be able to slit seed if I wait a few more weeks?

When I suggested waiting a few more weeks, I should have been more clear and made sure you understood that you'd then be dormant seeding. Maybe you understood that, but when I reread my earlier post, I didn't think it was very clear. The main thing is that you're waiting for temperatures to drop low enough that the seed won't germinate, so you'll probably need to wait until late October or even into November.

I'm not sure if slit seeding makes sense if you dormant seed. The point of slit seeding is to improve seed to soil contact, and with dormant seeding, that's accomplished by the snow melting and drawing the seed with it. I suppose if you slit seeded a dormant seeding you'd lose less to birds and insects and maybe get better germination. Whether it'll work or not probably depends on whether the ground is frozen or not, since the slit seeder probably wouldn't do well on frozen soil.

Thanks for explaining. I'll wait then until November to lay down the seed and will forgo the slit seeding and aeration until next fall.

I have a similar predicament like natureperson and had already scheduled a core aeration job. Can I sitll complete the core aeration and then overseed in November? I am 30 miles southwest of Chicago city.

You can go ahead and core aerate. It'll aerate the lawn and there may still be some extra soil exposed to help the seed to soil contact when you do overseed.