A ways back someone asked if it could be "too cold to snow" so I decided to ask Google...


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From METEOROLOGIST JEFF HABY http://www.theweatherprediction.com/habyhints/222/

One phrase that is heard time to time is that, "it is too cold to snow today". In actuality, earth's atmosphere 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 RH 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.

The phrase "it is too cold to snow today" probably originated as a misapplication of the relationship between temperature and the maximum amount of water vapor that can be in the air. When temperature decreases, the maximum capacity of water vapor that can be in the air decreases. Therefore, the colder it gets the less water vapor there will be in the air. 

Even at very cold surface temperatures significant snowfall can occur because: (1) intense lifting can produce significant precipitation even at a very low temperature, (2) the temperature aloft can be much warmer than the temperature at the surface. The relatively warmer air aloft can have a larger moisture content than air in the PBL, (3) Moisture advection can continue to bring a renewed supply of moisture into a region where lifting is occurring, (4) Even at very cold temperatures the air always has a capacity to have some water vapor. 
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Having an interest in weather stuff I did a little more searching on a phenomenon called "hoarfrost" which is when ice crystals form on tree branches.  I spent a day with some Civil Air Patrol radio geeks who got into giggles about the word when we were helping out with a crosscountry ski race up on the Tug Hill Plateau one very cold winter day.

This site has some good info if you're into cold weather:

http://nsidc.org/arcticmet/

Bruce

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