Live in the northland for any length of time and you'll hear the adage:  It can't snow when it gets cold - or - it's too cold to snow - or - something along those lines.  And it's true, there appears to be a correlation between the temperature and the chances of significant snowfall.  But what about the science behind the claim?  Is there factual evidence that can back the claim up?

Yes and no.

From a purely scientific (or meteorologic) standpoint, it can snow at any temperature.  But as the thermometer dips, the chance that it will snow diminishes.  Here's why:

Warm air can evaporate a lot more water than colder air. That is to say, there is more water vapor present for producing precipitation in warm air than in cold air, and when any air mass reaches the point where it can’t absorb any more vapor, it becomes saturated, produces clouds and finally precipitation.

As the clouds form, water droplets start to condense out of the air. As more droplets form, the greater the chance of them colliding and forming bigger drops. When they get big enough, they fall to the ground as precipitation and if the air is cold enough, they fall as snow. But when the air is really cold, it can’t evaporate as much liquid water to form water vapor, and therefore has less precipitate content for making snow.

That said, the adage that snow and cold don't mix makes a good armchair forecasting tool;  You usually have one or the other in any given time period - and usually never the two at the same time.

More information about this topic is available here.


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