Hydrologic response of central Sierra Nevada snowpacks to rainfall

Seven natural rain-on-snow events of more than 4.5 cm were studied at the Forest Service's Central Sierra Snow Laboratory near Soda Springs, in the Sierra Nevada of California, to determine if a pattern of snowpack response exists. All or part of the snowpack was below freezing beforehand but warmed to almost 0 degrees C by the time rain ceased. The typical response was a decrease in overall snow depth, and increase in average density, no change or a slight decrease in snow water equivalent, and only a small increase in runoff due to rain-caused melt. High density layers that increased substantially in density during a storm may have delayed downward flow and directed water laterally into existing drainage channels; this would refute the theory that rain water may percolate evenly through the snowpack with drainage occurring only after its storage potential is satisfied.