In the Pacific Northwest, average temperatures have been warming over the past century, somewhat more than the global average increase. The frequency of cold spells has decreased markedly. We do not see clear trends in precipitation, and variability is much greater than any subtle trends we might infer. The timing of snowmelt has been shifting to earlier in the spring. Projections of temperature increases are well outside the historical range of variability, although the projected changes in precipitation are well within the historical range of variability. Wetter winters and drier summers are expected, but the differences are not large relative to the variability. Warming will bring large changes in snowline and snowpack water storage in the mountains, with substantial reductions in snow-water storage at low elevations. Streamflow regimes are highly dependent on the presence of snowpack water storage: regimes in catchments with high-elevation snowpacks will change substantially, losing the typical snowmelt hydrographs, with more runoff in the winter and a decrease in summer low flows. Stream water temperatures are rising and are projected to continue to rise.