We present daily analysis of a 72-year snowpack evolution model driven by climate reanalysis data over a large Columbia River headwaters basin. Trends in cold content and total capillary retention reveal decreasing capacity to buffer against rain-on-snow flood events with the largest changes occurring during the last 5 weeks of the accumulation period. We demonstrate that seasonality of changes in factors related to snowpack buffering capacity is important when assessing rain-on-snow flood risk.