I’ve often heard people say that it’s too cold to snow. Is there ever any truth to that?

Blizzard on Park Avenue
Blizzard on Park Avenue

It’s true that when it’s very cold it won’t snow, but the statement is misleading. Once the temperature gets below freezing and other conditions are right for snow, the will-it-or-won’t-it question is purely a matter of the availability of water vapor. In most cases, in order for it to snow there must first be tiny droplets of liquid water in the air that can freeze into snowflakes.

But when the accessible supply of water is very cold, it strongly prefers to stay where it is, namely in the liquid form, so it doesn’t contribute much water vapor to the air. Thus, at very low temperatures there just isn’t enough water in the air to form those tiny droplets that could freeze and fall as snow. Of course, if it has been very cold for some time, most of the local water supplies will be inaccessible for vapor production anyway because they’re frozen.

In those National Geographic pictures of blinding, whiteout blizzards in the Antarctic, it’s not snowing—it’s blowing. Very strong winds are blowing around loose, already-fallen snow. And when did that already-fallen snow fall? During periods of milder temperatures (but still below freezing), when water vapor was more abundant.