Melting snow is like Chinese water torture

To be honest, I didn’t watch the whole process. After dinner I placed my rain gauge with its 8 inches of snow in front of the pellet stove. Every half hour or so, I would wander past and stare at its unchanging form in annoyance, then stomp off, muttering about the inefficiency of phase-change physics. Eventually I gave up and went to bed.

Melting snow is hard because it requires a change in the phase of water from solid to liquid, which takes a lot of energy – much more energy than required to just heat the molecules.

In fact, it takes a staggering 140 times as much energy to melt a given amount of snow as it does to raise the temperature of the snow by 1 degree. It’s easy to turn snow into slush, but much harder to turn it into water.

This is an example of a phase change. (Actually, the phase change is from ice to water, but snow is a reasonable facsimile.)

Folk wisdom is familiar with the difficulty of overcoming water’s other phase change, from liquid to gas: “a watched pot never boils.” I have a new motto: “A watched rain gauge never melts.”

This low-rent experimentation took place because I needed the result for my new sideline as a precipitation-measuring volunteer in the national program called CoCoRaHS or Community Collaborative Rain, Hail Snow network.

I’m one of a dozen or so active volunteers in Hillsborough County who measure moisture from the sky every day to help officials keep an eye on flooding, soil moisture and other issues. That requires knowing not just how much snow has fallen or is lying on the ground, but how much moisture is in the snow.

This can vary hugely, depending on whether the snow is light and fluffy (1 inch of water in 15 or more inches of snow) or heavy “heart attack” snow (1 inch of water in as little as 3 inches of snow), so called because of its effect on driveway shovelers.

The 8-inch snow column in my 4-inch-diameter rain gauge, melted down to 1.57 inches; a ratio of roughly 5 to 1. Pretty dense stuff.

Out in the Western United States, where mountain snowpack makes up a significant portion of the water supply, figuring out the moisture content of snow is important. There’s a ton of research out there on such things as measuring moisture as a function of radar backscatter patterns, not to mention the use of other technologies that can determine water content from afar.

For me, though, measurements depend on low-tech melting. I could buy a plug-in rain gauge that melts it automatically, but I think I can live without it.

CoCoRaHS recommends melting snow by pouring hot water on it – as long as you keep an accurate measure of how much water you’re adding, of course. After my stove experience, I think I’ll try that. There’s only so much excitement I can stand in my life.