We certainly don't get any astronomy done when it snows. Once the weather clears the snow has to be shoveled off of the dome before it can be opened for a night of observing.
The work is difficult, cold and dangerous (they wear safety harnesses), but the view from the top of the dome is fantastic.
Here are two members of the Palomar day crew as they shoveled snow off of the dome following one of last week's snow storms. Thanks to our Palomar Observatory Superintendent for the photo.