Too cold to snow?

January 17, 2008 7:57 PM

I've noticed that when the air temperature drops below a certain point that it won't snow. Is there any truth to this?

I have tried searching for an answer and have come up with nothing. Does this really happen? If so, why does this happen? What's the threshold as far as temperature?

posted by C17H19NO3 to science & nature (8 comments total)

Can it be too cold to snow?
posted by amyms at 8:05 PM on January 17

From the above link (which also has additional explanation and interesting content):

One phrase that is heard from time to time is that, "it is too cold to snow today". In actuality, earth's troposphere is not too cold to snow but rather it is "too dynamically stable to snow". Dynamic stability may be present due to low-level cold air advection, a lack of upper level divergence, and/or a lack of low level convergence. Also, if dynamic lifting does occur it may not produce precipitation that reaches the surface due to low relative humidity values in the lower troposphere.

The ingredients for snow are: (1) a temperature profile that allows snow to reach the surface, (2) saturated air, and (3) enough lifting of that saturated air to allow snow to develop aloft and fall to reach the surface. In a situation when it is said "it is too cold to snow" there is in reality not enough lifting of air that causes snow to reach the surface.
posted by amyms at 8:07 PM on January 17

As the air gets colder, the amount of water it can hold decreases, so very cold air tends to be very dry and so, there isn't enough humidity for significant amounts of snow to form. For example, note that that Antarctica is a desert, and a lot of the ice & compacted snow that is present in the middle of the continent is blown in from the coasts.
posted by bsdfish at 8:07 PM on January 17 [1 favorite]

It can't be too cold to snow, but at colder temperatures it's often too dry to snow

To quote:
So, to sum up, at temperatures near freezing, you can expect big honking snow flakes and lots of them. One those comparatively rare occasions when it snows near 0 F, you can expect individual snow crystals, but not very many of them because such cold air can't "hold" as much water vapor. Below about -40º, you can expect only very small crystals to fall, and very few of them at that.

As someone who grew up in the upper midwest, I can tell you that once it's below about 20, it rarely snows and whatever's falling is tiny ice crystals instead of what you'd recognize as snow flakes.

For lots more information, see this Google search.
posted by TungstenChef at 8:08 PM on January 17

And, as amyms' link points out, "If the air cools to truly frigid Arctic temperatures such as -40 C and below then the moisture capacity of the air will be so low that likely not much snow can occur. Only at these extremely low temperatures is the phrase "it is too cold to snow" fairly valid."
posted by bsdfish at 8:08 PM on January 17

Having lived in Fairbanks, Alaska for 7+ years, I can verify that it stops snowing around -35° (and -40 is the same in C and F). The air does fill with ice fog, however, which is very pretty but not too fun on the lungs.
posted by rhapsodie at 8:38 PM on January 17

I used to live in Minnesota, and sunny skies were always a bad sign in the winter; if it's too cold for clouds to form, it's too cold to be outside.
posted by you're a kitty! at 9:30 PM on January 17

The air does fill with ice fog...

Beware the pogonip!
posted by jquinby at 7:37 AM on January 18