At what elevation does the snow start in earnest (as in: snowshoes mandatory)?

I have all the winter gear, and I have 49 Colorado 14ers summitted (most of those known as our "hard ones" already completed), with 3 of those in calendar winter and several more in snow conditions of late fall/spring. I'm just curious where the snow really starts, so I can gauge how much travel will be slowed. I've put 40 miles and 11k vert under my feet before in 19 hr, but I know a winter ascent of Whitney is hard no matter which way you cut it.

Thanks!