This data release supports the study by Sexstone and others (2020) and contains simulation output from SnowModel (Liston and Elder, 2006), a well-validated process-based snow modeling system. Simulations are for water years 1984 through 2017 (October 1, 1983 through September 30, 2017) across a 11,200 square kilometer model domain in the San Juan Mountains of southwestern Colorado, United States that encompasses the Rio Grande Basin headwaters (HUC8 13010001). This data release also contains supporting field-based snow and meteorological station observations collected within the model domain during water years 2016 and 2017 that were used to evaluate SnowModel simulations. Sexstone and others (2020) provide details and summarize findings from the SnowModel simulations and supporting observations. SnowModel simulation output provided in this data release are stored in NetCDF files that have spatial (100-meter [m] grid resolution) and temporal (yearly) dimensions. Simulated SnowModel annual snow metrics (water years 1984 through 2017) in the attached NetCDF files include: mean winter (1 October to 31 May) air temperature (T; degrees Celsius [°C]), cumulative winter precipitation (P; millimeters [mm]), peak snow water equivalent (SWE; mm), SWE:P (ratio of peak SWE to winter P; m/m), snow-covered days (days with snow on the ground; days), total snowmelt (surface-water input into the soil that occurs when SWE greater than [>] 0; mm), snowmelt rate (rate the snow melts from peak SWE to melt out; millimeter per day [mm/day]), SM50 (water year day following peak SWE when half of snowpack has melted), peak SWE timing (water year day when peak SWE occurs), melt-out timing (water year day when snow melt out occurs), sublimation (total snow sublimation including surface, canopy, and blowing snow components; mm), sublimation:P (total snow sublimation to winter P ratio; m/m), 1 March SWE (mm), 1 April SWE (mm), 1 May SWE (mm), and 1 June SWE (mm). Supporting observations are provided in this data release in comma separated value (csv) files. Supporting meteorological station observations from three meteorological stations (daily mean values for the previous day) include: air temperature (°C), relative humidity (percent [%]), wind speed (meter per second [m/s]), incoming shortwave radiation (watts per meter squared [W m-2]), net radiation (W m-2), and albedo. Supporting field-based snow observations collected at 73 locations at a daily temporal dimension include: SWE (mm), standard deviation of SWE (mm), snow depth (m), and standard deviation of snow depth (m). An inventory and description of each of the files attached to the data release is provided below. Inventory of data release: URGB_SnowModel_study.xml: FGDC-compliant metadata file for the data release files. melt_doy.nc: NetCDF file of annual melt-out timing (water year day when snow melt out occurs) from SnowModel output . melt_rate.nc: NetCDF file of annual snowmelt rate (rate the snow melts from peak SWE to melt out; mm/day) from SnowModel output. peak_swe.nc: NetCDF file of annual peak SWE (mm) from SnowModel output. peak_swe_doy.nc: NetCDF file of annual peak SWE timing (water year day when peak SWE occurs) from SnowModel output. SM50.nc: NetCDF file of annual SM50 (water year day following peak SWE when half of snowpack has melted) from SnowModel output. snow_days.nc: NetCDF file of annual snow-covered days (days with snow on the ground) from SnowModel output. sub_p.nc: NetCDF file of annual sublimation:P (total snow sublimation to winter P ratio; m/m) from SnowModel output. sum_P_may.nc: NetCDF file of annual cumulative winter P (mm) from SnowModel output. sum_snow_RO.nc: NetCDF file of annual total snowmelt (surface-water input into the soil that occurs when SWE > 0; mm) from SnowModel output. sum_sub.nc: NetCDF file of annual sublimation (total snow sublimation including surface, canopy, and blowing snow components; mm) from SnowModel output. swe_p.nc: NetCDF file of annual SWE:P (ratio of peak SWE to winter P; m/m) from SnowModel output. swed_apr.nc: NetCDF file of annual 1 April SWE (mm) from SnowModel output. swed_jun.nc: NetCDF file of annual 1 June SWE (mm) from SnowModel output. swed_mar.nc: NetCDF file of annual 1 March SWE (mm) from SnowModel output. swed_may.nc: NetCDF file of annual 1 May SWE (mm) from SnowModel output. tair_winter.nc: NetCDF file of annual mean winter air T (°C) from SnowModel output. USGS_URGB_Met_Station_Data_WY2016-WY2017.csv Comma separated value file of daily mean value station observations reported for the previous day from three meteorological stations in the Upper Rio Grande Basin (URGB) including: air temperature (°C), relative humidity (%), wind speed (m/s), incoming shortwave radiation (W m-2), net radiation (W m-2), and albedo. USGS_URGB_Field_Snow_Data_WY2016-WY2017.csv: Comma separated value file of field-based snow observations collected at 73 locations in the Upper Rio Grande Basin at a daily temporal dimension including: mean SWE (mm), standard deviation of SWE (mm), mean snow depth (m), and standard deviation of snow depth (m). References: Liston, G.E., and Elder, K., 2006, A distributed snow-evolution modeling system (SnowModel): Journal of Hydrometeorology, v. 7, no. 6, p. 1259-1276. https://doi.org/10.1175/JHM548.1 Sexstone, G.A., Penn, C.A., Liston, G.E., Gleason, K.E., Moeser, C.D., Clow, D.W., 2020 (in review), Spatial variability in seasonal snowpack trends across the Rio Grande headwaters (1984 – 2017): submitted to Journal of Hydrometeorology.