Mid to late October marks the definitive return of the Pacific Northwest's wet season, with frequent storm systems bringing steady, soaking rains that reassert autumn's dominance over summer's dry months. October typically receives 3-6 inches of precipitation in lowland areas, a dramatic increase from summer's near-zero rainfall. Storm systems arrive with increasing frequency and intensity, bringing characteristic Pacific Northwest weather: gray skies, persistent drizzle punctuated by heavier downpours, and temperatures settling into the 45-55°F range. The rains trigger critical ecological processes including mushroom fruiting, salmon spawning runs, and the final phase of fall color as deciduous trees shed their leaves. Rivers and streams swell with runoff, waterfalls reach their full glory, and the landscape transforms from summer's browns and golds to winter's deep greens as mosses, ferns, and lichens rehydrate and flourish.