Annual summer, early winter, and total winter seasonal precipitation metrics, in millimeters, for Alaska and Northwest Canada. Seasonal metrics were calculated from monthly data with season lengths calculated from the piecewise cubic hermite interpolating polynomial calculated from monthly temperature data used to calculate our degree-day dataset. Input monthly data from the Scenarios Network for Alaska + Arctic Planing, consisting of downscaled CRU TS 4.0 historic estimates of monthly temperature were used for the period from 1901-2020, and downscaled CMIP5/AR5 projected estimates of monthly temperature were used from the period from 2006-2100. Summer precipitation and early winter precipitation were calculated from 1901-2100, and full winter precipitation from 1901-2099.