It Can’t Be Too Cold To Snow

“The wind had dropped, and the snow, tired of rushing around in circles trying to catch itself up, now fluttered gently down until it found a place on which to rest, and sometimes the place was Pooh’s nose and sometimes it wasn’t and in a little while Piglet was wearing a white muffler round his neck and feeling more snowy behind the ears than he had ever felt before.” —A.A. Milne, The House at Pooh Corner

In A Nutshell

As it turns out, all those bitterly cold days where there was no snow was a pure coincidence. Contrary to popular belief, it’s never too cold to snow. Snow relies on moisture in the air, and as long as that’s present, it can snow.

The Whole Bushel

It’s a bitterly cold morning, with temperatures that drop near freezing. The sun is shining, the sky is clear, and you can’t go outside without the inside of your nose freezing. At least it’s too cold to snow, right?

Wrong.

It’s never too cold to snow. If that were true, there would be a lot less snow at the poles.

Temperature does play a very clear role in the formation of snow (we all know that it can be too warm to snow). But the seemingly consistent trend of not snowing all that much when the temperatures plummet into the bitter cold regions of the thermometer have less to do with the temperature and more to do with what the cold does to the moisture in the air. As the temperature drops, so does the air’s ability to retain moisture. At the coldest temperatures, there’s only a little bit of water vapor left. Any snow that comes from that is going to be very, very light and probably hardly noticeable. Those who live in cold climates will recognize very-cold-weather snow, as it’s the thin, light coating of the white stuff that gets blown around by the smallest gust of wind.

Snow forms high in the atmosphere due to a process called expansion cooling. Air from near the ground rises, and as it does, it expands. Energy is used as it expands, cooling the air and reducing the amount of water vapor that can be suspended in the air. That water vapor is turned to rain or, if it’s cold enough, ice crystals and, in turn, snow.

The temperature in the atmosphere has much more to do with the formation of snow than the temperature we feel. When the atmospheric temperature is below freezing, the moisture there will crystallize into snow. Whether or not that snow makes it to the ground is dependent on ground temperature.

Once the individual ice crystals form, they can attach to each other to form snow. When the temperature is very, very cold—Arctic temperatures—it can impair the process by which flakes attach to each other. That’s why the annual snowfall in very cold places is actually very low. In the cases of bitter cold temperatures, the weather can sometimes more accurately be described as an ice fog rather than a snowfall.

Different atmospheric conditions and different temperatures mean different types of snow. Even the snow on the ground—called snowpack—can change and reform as the temperature rises and falls. Under very specific conditions, snowflakes can reach diameters of up to 5 centimeters (2 in) across. (No joke. We’re not talking about snow crystals here: Snowflakes are more technically groups of snow crystals.)

It’s rare that there will be a significant snowfall during bitterly cold temperatures, simply because the cold air can’t support the snow. So that just means that while school cancellations are off the table, you can still be forced to brush the snow from your car when it’s in the teens out. Noticeable snowfalls—and by that we mean an inch or more—have been recorded during temperatures as low as –15° Fahrenheit.

Show Me The Proof

Scientific American: What is the meaning of the phrase “It is too cold to snow”?
Chicago Tribune: Can it ever be too cold to snow?
National Snow and Ice Data Center: How Snow Forms