Characteristics of large snowfall events in the montane western United States as examined using snowpack telemetry (SNOTEL) data

Daily snow water equivalent records from the snowpack telemetry archive are used to assess spatiotemporal characteristics of large snowfall events ove r the montane western United States. The largest mean annual (leading) even ts are found in the Pacific Northwest and Sierra Nevada. The mean leading e vent lasting up to 72 hours typically accounts for 10-23% of the water equi valent of annual snowfall, with the largest contribution in the Arizona/New Mexico sector. For most of the West, snowfall events In the top quartile o f station distributions are most common during midwinter, but those for the Rocky Mountain states and Utah are more common during late winter or sprin g. Colorado also shows a secondary peak in large events during November. La rge midwinter snowfall events in the marine sectors, Idaho, and Arizona/New Mexico are spatially coherent in that when observed at one station, they t end to occur at surrounding stations. Large events are less spatially coher ent for drier inland regions. When annual snowfall is anomalously positive, there tends to be an increase in the number of snow days as well as a shif t in the distributions toward the larger event sizes. Opposite relationship s are observed for negative annual snowfall anomalies. These findings are i n accord with recent studies using lower elevation data, demonstrating that the probability of extreme precipitation events is altered during El Nine or La Nina conditions.