There is over at EYT a thread titled
Corn-Cycle-Information
and it has much of the usual conversation and speculation. I found one post, by "cesare", to offer some instructive perspective so would like to quote him here. Please feel free to offer your own knowledge and observations, either here or there..
"I think Aaron and bobs covered it well. It's all about radiation balance more than sensible heat, although when sensible heat (temperature) is low enough, of course it will freeze deep, which is a good thing. A shallow freeze can leave liquid water in the snow close to the surface, so I don't like to count on a radiation freeze to lock things up.
The way it works is... every object in the universe that has a temperature above absolute zero emits a spectrum of electromagnetic radiation proportional to its temperature. This process causes the temperature of the object to decrease, provided it doesn't have a thermonuclear or other process internally generating heat. Since snow is not a star or a mammal it gets colder as it emits.
So why do clear atmospheric conditions matter? Because if the atmosphere has a lot of water vapor in it or water liquid (clouds) these molecules abosorb that radiation and return half of it to the earth's surface in the form of primarily long wave radiation due to their temperatures. Snow happens to behave as a black body in the long wavelengths, meaning it is a nearly perfect emitter and absorber of electromagnetic radiation in those wavelengths. Therefore, it absorbs all the longwave radiation incident upon it. If there are no clouds, that radiation is free to escape to space. When it is clear, the radiational cooling of the surface of the snow can lower its temperature to below the freezing point. Hence the term radiational cooling. But the thing is, this is mostly affecting only the surface of the snow because the snow below the surface has snow above it that absorbs its longwave radiation and re-emits half of it back down where it is just re-absorbed.
If the air temperature is a little above freezing, the surface of the snow can freeze at night. But it will not be the deep freeze that is needed to lock up the liquid water as ice.
Finally, under melt freeze metamorphism, the liquid water that does refreeze, does so mostly as a medium that fills the gaps between the grains of snow. But each time it freezes and thaws, some of that liquid remains coating some of those grains and in this way the grains grow progressively larger with each melt/freeze cycle. And as the surface melts during the day, we see that the window of opportunity for perfect corn can be very brief, as others have mentioned. This is especially true with corn snow in a relatively thinner continental snowpack. Sometimes we can get a half hour or so of great skiing, followed by saturated mush that melts completely almost as quickly as it turns to mush around the margins of the snowpack where it is thinnest. That's why the corn skiing is a lot better where the snowpack is thick and consistent, remaining below freezing long after the air temperatures have risen above freezing."
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