Potential Tropical Source of Predictability for West Coast Snowpack

Understanding the patterns of snow accumulation is of critical importance for many areas throughout the United States. Fluxuations in snowpack can determine the availability of water resources, threat of flooding hazards, and access to recreational opportunities. Forecasting snowpack depends on many factors, with one source of its predictability being the Madden-Julian Oscillation (MJO). The MJO is an irregular, intraseasonal variation in the tropics fueled by the large-scale coupling of atmospheric circulation and deep convection. While the phenomenon most clearly manifests itself as anomalous rainfall over the Indian and Pacific oceans, the MJO impacts other parts of the global weather system (especially at the mid-latitudes), including precipitation in the Western United States. To understand the potential influence of the MJO on snow accumulation in the West Coast, we compare MJO indices with Snow Water Equivalent (SWE) measurements from Snow Data Assimilation System (SNODAS) Data Products. Three analysis regions are determined by the extent of the SWE data—Northern Cascades (Washington), Southern Cascades (Oregon), and Sierra Nevada (California)—with Washington showing the strongest intraseasonal (45 day) signal in the power spectral density function of the SWE gradient. Further analysis in the Washington region shows peak SWE accumulation rates when MJO precipitation center is over the Indo-Pacific Maritime Continent, and the highest percentage of days with active snowfall when its center is over the Indian Ocean. The results from these analyses suggest the need for further exploration into the significance of the MJO influence in Washington winter climate systems.