My kale bed has been buried under the snow for a good number of weeks now, and I wanted to see how the plants were doing. So I decided to uncover one of the plants. I brushed away a top layer of relatively soft snow, and then had to break through a heavier, icy crust before exposing the plant.
This particular plant seemed to be doing quite well. Its upper most leaves were wilted and damaged, but the lower ones seemed fine. I separated three of the lower leaves from the stalk and found them to be crisp and supple, with only a little frost damage on one of them. I covered it up again, and didn't bother inspecting the other plants.
So I've declared this winter planting and harvesting experiment a success! We've had plenty of snow and consistently sub-freezing temperatures for several weeks now, and the kale still seems to be thriving, with nothing but a layer of mulch below, and a cover of snow above, to protect it. Next season, I'll try planting a larger collection of different varieties of kale plants, and we'll see how that goes. It would also be interesting if these particular plants go to seed in a few more months, when the weather warms up.