Weather Whys: Why snow melts or disappears in subfreezing temperatures

Weather Whys

Water can exist in various stages — solid, liquid or gas. When ice and snow melt we’re observing the water cycle in action. We know we need temperatures above freezing to melt snow. So why does snow still disappear in the middle of winter when it’s way below freezing outside?

There are two ways snow can disappear in subfreezing temperatures. First, the most common way is when the sun heats the ground to above freezing. This allows ice and snow to melt even though air temperatures may be below freezing. The darker the surface, like asphalt or roof tops, the warmer it can get.  


The second way snow disappears in subfreezing temperatures is through a process known as sublimation. Where a solid bypasses the melting phase and turns straight into a gas. 


Dry ice form of sublimation. It’s a solid that turns into a gas. In the real world, this very same process is jump started in the snow by the Sun. 

Sublimation happens best on sunny days where the sun creates enough energy to allow the solid water to turn to a gas… skipping the melting phase. 

Snow can also sublimate with strong enough wind…  this evaporates the snow before it has a chance to melt. 

You witness sublimation on a regular basis. Solid air fresheners that get smaller with time.. they’re undergoing sublimation as they release their scent. Moth balls get smaller, that’s sublimation. Ice cubes left for a while in the freezer will also shrink in size due to sublimation. 

Of course these don’t have the sun to spur the energy to sublimate, they do so over time with certain temperature and pressure combinations.

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