We compiled the Landsat Level-3 Fractional Snow Covered Area (fSCA) product (Painter et al. 2009, Selkowitz et al. 2017) for the tiles intersecting the study area for 2000–2017. The product estimates fractional snow cover for each 30-m pixel, with possible values of 0% and 15–100%. We masked all data that was not “Clear” (pixel value of 0) in the Revised Cloud Mask layer. Then we calculated the median snow cover for bimonthly periods from all the Landsat imagery for the period (e.g.,all images for 1–15 May, 2000–2017). We assigned the median snow cover fraction to the midpoint of the period (e.g., 8 May). Then we interpolated to a daily time step (e.g., a pixel that was 80% snow covered on 23 April and 20% snow covered on 8 May was estimated to 50% on 1 May). Finally, we stacked the daily observations, and extracted the last date with ≥15% snow cover as the “last snow day.”