Yeah- that's the bad part about our beloved snow- stacks up sometimes and stops up all the anemometers! I actually waxed my 5n1 housing with some NuFinish (the old standby in the orange bottle!) and it seems to help snow and ice "sluff off" a bit sooner, if not preventing it from sticking too well in the first place.
Fortunately, the temperature and humidity chamber is fairly well ventilated for an all-in-one design, so it will not be affected by the snow cap in most instances.