A little won't do. It has to be 99.999...% correct.Similar question raised a man with a horse when he saw a car. How to drive a car where are no roads? He answered to himself: you buy a horse!
Please have a little faith in technology
FSD can't take any risks, so it has to be sure.
I'm not entirely disregarding the possibility that a solution can be found. I just kept thinking that often times we drive based on memory of what we saw when the snow was not there... For example, a stop sign that is entirely covered by a sticky snow. If you drive there often, you know it's there. Location of turn lanes, etc.
Just took my daughter for her 2nd ever drive to a parking lot after the fresh snow. To do some doughnuts and have some fun. So, there are curbs in certain places around the lot and in the middle, which I can recognize by the slightly raised snow levels or trees/poles sticking out. Couple of times she drove right over those curbs, b/c she's a new driver and not used to paying attention to those things and staying away. I just saw how this can be a challenge to an FSD - if it is not sure that it's going to leave the road and end up in the ditch, then that risk should not be taken.
The other concern is related to cameras being obstructed as @bdy0627 mentioned.
I noticed that during a snowfall I start getting sounds related to an obstruction ahead and it is actually showing it on the screen ahead of the car when nothing is there, so that kind of confusion is not helpful for achieving 99.999%. Maybe this can be improved. But an ice buildup would certainly put cameras out of commission. Need to add heaters there.