I found some kind of waterproof shell for it, but it wasn't raining, so I figured I didn't need it. My sweat didn't get to it (other layers underneath) but snow fell on it, and it was rendered useless.
Wear a waterproof
and breathable shell with a hood - Gortex, Enervex, et al over a polyester fleece layer of appropriate thickness for temp and activity. Leave the down jacket in its waterproof stuff sack during the day. Maybe even consider leaving the down jacket at home.
Also scary: A lot of snow fell on my head. It was welcome at first, because I was hot from hiking but I had snow tangled up in my hair. The snow melted, and then refroze so when the sun went down it was like I was wearing an unmovable ice cap.
Wear a breathable shell with a hood. And for dog's sake, brush the snow out of your hair before it refreezes. Regularly brush it off your clothing as well.
And wear a breathable shell.