'Too cold to snow' is also a
phrase used in
England. I suppose it could have some
merit, the amount of
moisture air can 'carry' is related to
temperature; the warmer the
air, the more water it can carry, implying really cold air can't carry water, so it can't
snow or
rain. The niggling point I have is that if you have warm, water laden air, travelling over
your cold region, the air cools, can't hold its water , and it'll rain. If your air is cold enough, this water might well fall as snow.
There is however, I believe a valley in the
antarctic where it really is too cold to snow. This
valley is so far from the ocean, all the moisture from the air has already
precipitated out by the time it gets there. It's so dry there you can see
mummified seals that are thousands of years old, perfectly
preserved.