The region has a temperate climate with wet winters and dry summers. About 90 percent of precipitation in the watershed comes between October and May. Precipitation in the basin varies greatly with elevation; about fall annually in the Willamette Valley, while the Three Sisters in the high Cascades can receive in a year. Above , about 35 percent of precipitation falls as snow, and at and higher, over 75 percent of precipitation is snowfall. At these elevations, melting snow beginning in the spring season brings more cold water out of springs under the permeable rock, increasing the McKenzie's flow and maintaining cold water temperatures in the river and its tributaries. Along the lower McKenzie, however, winter rain slides easily off the less permeable rock and erodes sediment into the river.