Frozen snow on goggles' outer lens
For instance you get out of a cable car or a gondola, the snow in a blizzard melts on your relatively-warm outer lens and re-freezes instantaneously, leaving a layer of frozen ice crystals on it and blocks your vision.
Another scenario would be on a chairlift. It is sleeting at the valley and the watery ice crystals deposit on to the outer lens. At the summit the temperature is below freezing and the sleet freezes and sticks firmly on the lens.
What would you do in such occasion?