Cleaning snow from the roof in below freezing weather

X2 on thaws and freezes. We try and keep the areas around vents clear at a minimum. The total depth of snow accumulation is less of a worry than a warm spell followed by rain. IF......you do decide the snow must come off, careful snow raking around covers, vents, etc. and if you do get on the roof, be sure to stand on the unshoveled part, that cleared area is going to be very slippery.