Sam Cohen, in Rosedale, asks: "I hear a lot of people saying, on days when it is really cold, 'It's too cold to snow.' My answer is, 'Then how does it snow in the arctic?'" It's never too cold for snow in Maryland. But to have snow, you need ample moisture. And the colder it is, the less water vapor the air can hold. Even arctic air can produce snow if it cools to its dew point, or if there is warmer, wetter air above it. But at polar extremes -- say, 40-below -- snow is rare. The South Pole is a desert of blowing snow.