We had about two inches of snow around here last night. Much of it melted today even though I don’t think temps went above freezing all day. Can someone please explain to me why this happened?
Thank you.
Radiation from the sun. Even though the air temperature is less than 32F, the sun can heat surfaces hotter than that. For example, put your hand on a piece of metal that’s been out in the sun all day (in the summer). It’s much hotter than the ambient air temperature. As long as heat is radiating into the object (snow) faster than it can be carried away (by the air), the snow will melt. In low-humidity, low pressure situations, the snow will sublime. That is, go directly from the solid phase into gas, completely skipping the liquid phase. This explains one big difference between “good” and “bad” snow for skiing. If it’s sublimating, the snow will stay much more dry and powdery.
Also, the ground may be quite a bit warmer than freezing.
That is the answer, in the ground. If the ground is not cold enough when snow falls, its not going to stay many days.
If the ground is not cold enough when the snow falls, it’s not going to stay any days.
Now that’s one of the stranger double/simul posts I’ve ever seen.
Particularly since they were four hours apart… :dubious:
Maybe I have an evil twin?
And the second one has an apostrophe and a misspelling.
That’s why in colder climates I prefer an asphalt driveway to concrete. On a sunny day the asphalt driveway will warm up and effectively melt snow and ice off a driveway. A concrete driveway you always get stuck with patches of ice that never seem to want to melt.
That’s not a misspelling, that’s the whole point of the second post. If the ground isn’t cold enough, not only will the snow not stay *many * days, it won’t stay *any * days.
Thanks, CookingWithGas.
I probably should have quoted the previous post, and italicised “any”. I did flub the ', though.
I always tend to find you in the heat transfer threads, hence theusername ?
Even if the ground is below freezing, frozen water will sublimate because the air is relatively dry.
Brian
Thank you guys. That’s what I get for not taking physics in high school.
Actually, *you * got the apostrophe right. It was erroneously absent in the prior post.
I don’t have any significant background in physics other than two semesters of classical mechanics and general physics, and a course each of quantum mechanics, and physics of music in college. But many of the heat transfer discussions on the Board involve basic principles. See my post in your referenced thread.
This is the real answer to the OP. Snow has a LOT of surface area and evaporates quite readily, even when kept below freezing and unexposed to sun.
Isn’t pretty much all of the sun’s heat reflected away from the snow because it’s white?
If I remember high school physics properly, the reflection won’t be 100% efficient in that some of the light will be absorbed by the snow, and some won’t reflect and instead go further into the snow.
If its fluffy snow I would imagine some of the sunlight would reflect further into the snow and use all its energy reflecting around. Also, I’m not sure what sort of gaps sunlight can pass through, but since an individual snowflake has gaps in it that may allow the light to penetrate further in as well.
Can you kindly explain why snow lasts for several weeks under trees, and along fences, where the sun don’t shine (hehe)?
No, pretty much all of the sun’s light is reflected away, but that’s just the very narrow spectrum of light in the visible regime. If you’re wearing a white shirt in the summer, it’s a little cooler than a black shirt (5C or so, IIRC), but it can still get pretty darn HOT!
cooky173 , sunlight can penetrate gaps that are bigger than it’s wavelength. Visible light (for humans) is about 380nm to about 780nm.