Contiguous U.S. annual snow persistence and trends from 2001-2020

Snow persistence (SP) or the snow cover index (SCI), is the fraction of time that snow is present on the ground for a defined period. Cloud covered index (CCI) is the fraction of time that there is no data, cloud, or sensor saturation for the same period. SP and CCI were calculated on a pixel by pixel basis using MODIS/Terra Snow Cover 8-Day L3 Global 500m Grid, Collection 6 obtained from the National Snow and Ice Data Center (NSIDC). January 1 - July 3 SP was calculated for each year as the fraction of 8-day MODIS images with snow present. The selected period brackets the temporal extent of peak snow accumulation to complete snow ablation in most parts of the western United States. The July 3 date is used because the 8-day MODIS image does not fall on the first of the month in this case. This data release contains gridded 500 m MODIS snow persistence for years 2001 to 2020 along with accompanying pixel by pixel trends for the entire contiguous U.S.