Angular snow with poor bonding created from large temperature gradients within the snowpack.

How faceted snow is formed:
Faceted snow forms from large temperature gradients within the snowpack. Big word alert!–temperature gradient. A temperature gradient is simply how fast temperature changes over a certain distance within the snowpack. Why? Because it’s a fact that warm air holds more water vapor than cold air. This means that temperature gradients also create what we call “vapor pressure gradients”–more water vapor in one place than another. And what happens when you concentrate something–especially a gas? It wants to diffuse–move from areas of high concentration to areas of low concentration. When water vapor RAPIDLY diffuses it changes rounded crystals into faceted ones–changes strong snow into weak snow. In other words, temperature gradients create potential weak layers that can kill us. That’s why we pay so much attention to them.

So, large temperature gradientâ€”how large is large? For snow of an average snowpack temperature, say around -5 degrees C, the critical temperature gradient is about one degree centigrade per 10 centimeters (1 deg C. / 10 cm.). In cold snow, say colder than -10 deg. C, you need a higher temperature gradient to cause faceting and in warm snow you need slightly less.

For example, let’s stick two thermometers into the snowpit wall, one 10 centimeters above the other (about 4 inches). Say we measure a difference of only 1/2 deg. C. in 10 cm., it means that equilibrium snow is growing (snow is getting stronger). If we measure a temperature difference of 2 deg. C. in 10 cm., it means that faceted snow is growing (snow is getting weaker). All you have to do is to find a faceted layer in the snowpack, measure the gradient and you know whether the layer is gaining strength of loosing strength. Cool, huh? This is actually a powerful forecasting tool.