I’m in the same area. I didn’t have an indoor last year. I only missed about a week and a half straight of no riding and that’s just because the ground wouldn’t thaw. The other times, I rode at least 2 or 3 times a week. Now that might have been only hacking because of hard ground or trotting around in snow. I rode in the snow.
It really depends on the location of the ring, the type of footing, and how often it’s maintained.
My ring was in mid afternoon sunshine and was stone dust meaning that it thawed and drained extremely well. Also, it was drug as often as possible when thawed.
I also rode in wind and I rode at night. I have a good girl that mostly behaves.