Drivers of Snowfall Accumulation in the Central Idaho Mountains using Long-Term High-Resolution WRF Simulations

The Western United States, an economic and agricultural powerhouse, is highly dependent on winter snowpack from the Mountain West. Coupled with increasing water and renewable electricity demands, the predictability and viability of snowpack resources in a changing climate is becoming increasingly important. In Idaho, specifically, up to 75% of the state’s electricity production comes from hydropower, which is dependent on the timing and volume of Spring snowmelt. While we know that April 1 snowpack is declining from SNOTEL observations and is expected to continue to decline from GCM predictions, our ability to understand the variability of snowfall accumulation and distribution at the regional level is less robust. In this paper, we analyze snowfall events using 0.9 km-resolution WRF simulations to understand the variability of snowfall accumulation and distribution in the mountains of Idaho between 1 October 2016 – 31 April 2017. Various characteristics of snowfall events throughout the season are evaluated, including the spatial coverage, event durations and snowfall rates, and the relationship between cloud microphysical variables—particularly liquid and ice water content—on snowfall amounts. Our findings suggest that efficient snowfall conditions—e.g., higher levels of elevated supercooled liquid water—can exist throughout the winter season but are more impactful when surface temperatures are near or below freezing. Inefficient snowfall events are common, exceeding 50% of the total snowfall events for the year, with some of those occurring in peak winter. For such events, glaciogenic cloud-seeding could make a significant impact on snowpack development and viability in the region.