Late enough not to risk any warm up is best--and the northeast is getting another warmup into the seventies (for me, anyway) this week.

Hence my recommendation to drop just before the first major snowfall. Usually any significant warming trend is behind you, and if it isn't, it won't last long enough to cause a major problem during most years.

Tentatively, I'd say that the earliest normally acceptable date for dormant seeding is around December 15th in most locales during most years. January 15th would be safer as we often get a thaw around my birthday, just after the New Year.

Thanks Morph. Do you think that I could dormant seed, let it sprout and still put down a pre-m to stop the crabgrass without severely impacting the grass? I'm trying to establish more grass than crabgrass in an area so it doesn't need to be a thick lawn, just one that's not all crabgrass! This is the "dogleg" area we've been talking about

Most pre-emergents can do damage if applied before the third mow (the roots are shallow enough that the pre-M can harm them). Third mow probably won't be until late May or June, but at that point you can apply the pre-emergent to stop any summer-sprouting crabgrass. On the up side, crabgrass doesn't sprout heavily until temperatures really rise.

What managed to sprout early can be spot treated with Weed B Gon Plus Crabgrass Control.

Great. I have tenacity too if that would be better. Would it be better to dormant seed or just seed as soon as the snow clears? I'd think dormant seeding would get it going as early as possible.

Dormant seed. It gives the seed time to settle to the soil (snowfall really helps out with that), get damp (snow), and go through pre-germination, which is the weakening of the seed coat in preparation for sprout (not usually much of an issue for grass seeds).

Tenacity would work! Some paling out of the new grass is going to result, but that'll reverse.

Great - tenacity over weed be gone then?

As a pre-emergent, it would also work. You'd get a month of coverage, although you could also use it as a post-emergent on CG if you'd like to do that.

Really, both work very well as a pre-emergent for CG (and I use Tenacity on the rare CG plant in the garden as I don't have WBG on-hand).