can it be 'too cold to snow'?
TRANSCRIPT
1. Introduction
An oft posed question is, “Sod me it’s bloody
freezing, so why isn’t it snowing?!” the repost of
which is often heard to be, “Because it’s just too
cold, old chum”. Well can it be too cold to snow?
2. Temperature and moisture
First we must examine snow. Snow is the common
term for a collection of snowflakes, a particular
form of water ice produced in clouds which then
falls to earth. Snowflakes form when the
temperature is below freezing as water changes
from its liquid form to ice, the shape of the
snowflake depending on several factors1.
The idea that it could be too cold to snow seems
just chuffing crazy to anyone from a warm climate.
However Barrow, in Alaska, gets less snow on
average per year than Chicago despite being on
average a full 39ºF colder,2 . In addition people
from cold climates may notice that a colder winter
does not relate to more snow.
We know snowflakes are formed from water vapour
which freezes. An important point to note is that
warm air can contain more water vapour than cold
air, as shown in table 2.1.
Temperature (ºF) -40 0 32
Water vapour (g) 0.07 0.60 2.70
Table 2.1 Grams of water vapour per cubic metre of saturated air at a given air temperature.
When an air mass reaches the point where it can
contain no more vapour condensation occurs and
clouds form, inside clouds droplets collide, and
when large enough fall as precipitation. At 32ºF
more water vapour can be present in the air, so
precipitation can easily occur, but at 0ºF or below
there is not enough water vapour present to allow
easy formation of large droplets which would fall
as precipitation3.
The figures in table 2.1 demonstrate that below 0ºF
snowflake formation is more difficult, however
they assume the maximum saturation of the air with
water vapour. Snowfall in-fact depends on two
other factors; a temperature profile allowing snow
to reach the surface; and enough lifting of the
saturated air to allow snow to develop aloft. Or put
another way; it’s gotta be cold enough so it doesn’t
melt halfway down; and it’s gotta get high enough
to form.
3. Conclusions
So snow does not wholly depend on temperature
but rather a combination of factors, the answer
would generally be more accurately put as “It’s too
dry to snow” demonstrating that there is too little
moisture in the air to form precipitation. This is
however more common at lower temperatures,
although the property of ‘air lifting’ cannot be
ignored as a factor in the lack of snow fall.
The ultimate answer to our question is of course
yes. But we stipulate that the temperature must be
at, or near, absolute zero - 0K or -459ºF as at this
temperature all air, including water vapour
condenses and loses all molecular energy making
the formation of snowflakes impossible4.
1 ABOUT INC. Snowflake Chemistry. Updated 2006. Accessed 22 August 2007. <http://chemistry.about.com/od/moleculescompounds/a/snowflake.htm>
2 STRAIGHT DOPE. “Does it ever get too cold to snow?”. Updated 2002. Accessed 22 August 2007. <http://
www.straightdope.com/mailbag/msnow2cold.html>
3 WEATHER IMAGERY. “Too cold to snow?”. Updated 2005. Accessed 22 August 2007. <http://weatherimagery.com/blog/too-cold-to-snow/>
4 HABY, J. “Can it be too cold to snow?”. Updated unknown. Accessed 22 August 2007. <http://
www.theweatherprediction.com/habyhints/222/>
CAN IT BE ‘TOO COLD TO SNOW’?Hugo King
Snow Research International
2650 Snow Road, The Arctic