When it’s bitter winter and the sky is leaden grey there’s invariably some bright spark who’ll stare at the sky, sniff and say “it sure is cold , but too cold for snow”. What ? surely it can’t be too cold for snow , the stuffs frozen water it needs sub-zero temperatures to exist ? So the question we’re going to look at in this article is … “Is there a basis to the weather folklore about it being “too cold for snow” ?
It turns out we should be very wary of questions about the weather, as the “obvious” answer all too often falls foul of some more subtle feature of the way the weather works: and thus it proves here.
the temperature is pretty irrelevant if there’s not enough moisture in the air to form ice crystals
On the face of it, as snow is made from ice crystals, which form at any temperature below the freezing point of water, the idea that the temperature can be too low for snow to form seems to contradict elementary science. Yet this overlooks the fact that the temperature is pretty irrelevant if there’s not enough moisture in the air to form ice crystals – and bitterly cold weather is often the result of relatively moisture-free high-pressure systems. So, during a cold snap it can indeed be “too cold for snow” and we must wait for a warmer and wetter low-pressure system to arrive. If one follows hard on the heels of a cold snap, there is a much better chance of the snow settling, as it takes some days for the ground to cool sufficiently to prevent the snow crystals melting on contact.
So there you are … it can be “too cold for snow” after all.