5.2.6 Rain

New event: Rain

Let's say that in the six days following the initial snowfall, the original 16-in snowpack became slightly denser while its depth decreased slightly. The SLR was about 11:1.  Then the surface temperatures warm, a storm approaches, and significant rainfall occurs. Most of the rain (about 0.2 in or 0.5 cm) occurs at 36°F (2°C). The top of the snowpack is transformed into a high-density layer, with some crust forming after the rain and the passage of a cold front. As is typical in mountainous locations, snow falls after the cold front passes and is wet and heavy, with a liquid equivalent of 2.4 cm (1 in) and an SLR of approximately 8:1 to 9:1.

Depiction of a rain event followed by a wet, heavy snowfall

Now we have a relatively thick layer of crust and high-density snow that's 20 cm (8 in) down in the pack. Snow grains in the crusted layer have a low degree of bonding, so the presence of this weak layer can decrease friction, thereby reducing the stability of the snowpack.