[GEOFFREY DUFFY]

GEOFFREY DUFFY"  asked the Naked Scientists:

Snow...
  
My mother uses the expression "It's too cold  to snow".  I understand this perfectly i.e. we have really cold weather  without snow, but things feel warmer just before snow  starts to  fall.  I wonder whether there's a simple explanation for this, thick cloud  cover comes to mind, for instance, acting like a blanket and trapping  warmth...but which then results in snow?  We'd be really very grateful if  you have any thoughts on why this is.
  
For my own part, I can 'taste' snow long before  it falls...only when I'm out in the fresh-air, not indoors.
  
 Thank you
  
 Geoffrey Duffy

(Great radio show!)

What do you think?

[paul.fr]

Hi Geoffrey,
It is never too cold to snow, it can and has snowed at temperatures of -40 degrees. Although it is very rare. Some people will claim to have seen very small particles of snow when the temperature was pretty low, but these will more than likely be freezing fog.

When it does snow at very low temperature the snow will fall mainly as small pellets, like hail.
http://en.wikipedia.org/wiki/Graupel

Also, when you wonder why it seems to get warmer just before it starts to snow. Well this actually ties in with the "too cold to snow" saying. During the winter when you have been under a run of cold weather, but you will also get ridges of high pressure before the next front moves in. This high pressureoften means you will have night skies of none or considerably less cloud, this makes things colder and can and does lead to a frost.as this high pressure is then replaced by by another low pressure system this makes the weather warm up, and as the temperature rises towards freezing the risk of snow increases and there is a greater chance of snow - some prolonged.

This link may also be of interest
http://www.thenakedscientists.com/forum/index.php?topic=12140.0

There is an old weather saying that holds true

"when the icy wind warms - expect snow storms"