Why is fresh snowpack difficult to get rid of?

You get your first big snow event of the winter season! Right out the gate, it is apparent a heavy snowfall brings a certain uniformity to the landscape by encasing it in what could be described as a “smooth, white blanket”. In this regard, the original landscape changes its identity in important ways affecting future weather. Specifically, the average albedo is temporarily, but fundamentally, different after the arrival of a snowpack. Albedo quantifies, as a percentage, a material’s reflectivity of incoming solar radiation. The lighter a material’s color and smoother the surface, the greater the reflectivity. Consequently, higher versus lower albedos result in cooler surfaces since a greater proportion of sunlight was unable to be absorbed and later be reemitted back into the environment as infrared radiation (what we feel as heat). Fresh snow is about as efficient as you can get on the planet for higher albedo purposes (~95%). For comparison, a typical pine forest’s albedo is much lower between 5-15% (lots of dark, rough surfaces to take in sunlight).

Snow has another trick up the sleeve! Although fresh snow contributes minimal new infrared radiation due to a high albedo value, it also happens to be at the same time an excellent heat sink by absorbing nearly 100% of incoming infrared radiation. The removal of infrared radiation (thermal heat) from the air is yet another cooling mechanism. The pairing of high albedo and high infrared emissivity properties for fresh snow is why temperatures often plummet substantially in a local area after a heavy snowfall event as skies clear!

We are not done! Snow is water in a frozen state and like liquid water still has a relatively high specific heat capacity (energy needed to raise a substance by one degree Celsius). Therefore, snow can keep absorbing quite a bit of infrared energy before warming past the melting point. The combination of these three unique physical properties (high reflectivity, high heat absorption potential, and high heat storage capacity) is an example of a positive feedback, since snow possesses an inherent ability to reinforce environmental cooling, which helps preserve itself in the landscape.

Photo Credit: Jonny William Malloy