Yesterday's "SnowEater" Conditions

Yesterday was a net loss for what little snowpack that we had at pretty much all but the highest elevations.  We didn't have a lot of snow on the ground yesterday morning, but a couple of inches was lingering on shady north aspects, and most of that snow is gone today.

Yesterday.  Source: Alta.com.

Today.  Source: Alta.com.

Here's another perspective looking up Collins Gulch.  Yesterday there was a white strip in High Rustler and environs, and spotty snow down almost all the way to the base (unfortunately I didn't grab an image).  Today, gone.

Today.  Source: Alta.com

During fall and winter, it's very hard to melt snow on north aspects when skies are clear, even when the temperature is well above the melting point (0ºC).  On these aspects, there is simply not enough energy from the sun to melt snow when the sun angle is low, and the energy transferred from the relatively warm atmosphere to the snowpack is insufficient to drive significant snowmelt.

Yesterday, however, we had a boost in energy input to the snowpack from two additional sources.  One was the rain, which when it hits the snowpack cools to 0ºC, releasing energy for the melting of snow.  The other was the cloud cover, which provides long-wave radiation for snowmelt, a process sometimes referred to as "greenhousing" and which also results in cloudy nights not being as cool as clear nights.  Thanks to those two energy sources, poof, what little snow we had is now gone except in the highest elevations.

During winter, when the sun angle is low, the worst-case scenario for snowmelt is not a warm, sunny day, but a warm foggy day with rain.  A couple of hours of snowmelt is about all you get on a warm, sunny day during winter, but fog and rain work 24/7.  In the eastern United States, warm, foggy, rainy days just destroy the snowpack, creating "snoweater" conditions.  Here in Utah, such effects are sometimes seen in the lower elevations.  For example, in December and January, snow will linger in shady areas in the Salt Lake Valley under clear skies even if it is well above the melting point, but if you get a day with rain and low clouds, it can melt away.