Evergreens can incur severe damage over the winter simply because they hold on to their needles. It leaves them susceptible to the elements far more than deciduous trees. Besides loosing moisture, columnar evergreens can be damaged in form by the heavy snows.
Columnar evergreens tend to catch snow just inside their branches causing them to bend outward and look disfigured in the spring if heavy snow persists. You can knock it off as it falls, but that can be a lot of work. If you wrap your arborvitae and junipers in a bird netting or strips of cotton/nylon it can support the trees tight upright form through the winter. Come spring the damage is minimal to none!
