 Like most of the Inland Northwest, Winthrop experiences a humid continental climate (Köppen "Dsb"), with cold, snowy winters and very warm summers with cool nights and little rainfall.Winthrop and Mazama recorded the coldest temperature ever measured in Washington state at () on December 30, 1968.The hottest temperature recorded in Winthrop was on 27 July 1939, but frosts can occur even in summer.