I have seen this before, but not to the extent it is right now. Overnight temps fluctuated between 29 and 33F, all the while it was snowing. Sort of like occasionally spritzing the snow with a little water. Slowly, it builds a loose ice pack on top of the snow. Gets thick enough it will support a lot of weight.
It is 30F right now and expected highs are 36F, with clouds hanging around all day.