At temperatures below freezing, when the air is saturated with vapor, fog droplets freeze upon contact with nearly any surface. When this happens, crystalline like deposits grow into the oncoming wind. Relentless winds and the cold moist air often produce remarkable accumulations of rime ice, where everything is coated with a frosty mantle of white. The observatory's instruments need to be tended to regularly during riming conditions in order to rid them of their icy sheaths. The windy and changeable weather on Mt. Washington is attributable to several factors.
Nearby peaks act to funnel the winds, much as skyscrapers do along city streets.
Winds blowing between the peak and the tropause become constricted or compressed, which acts to further accelerate wind speeds. The summit observatory is built to withstand 300 mile per hour winds. It's made of steel and concrete, and all windows are double-paned with a reinforcing layer of bulletproof glass. Nonetheless, according to observers, some gusts seem to make it shutter, and even when you can't feel it, you can nearly always hear it. One observer described it as a screaming monster trying to get inside.