The best weather for visiting the North Cascades generally occurs between mid-June and late-September. Snow is off all but the highest trails by July. Autumn and Spring are becoming more popular for visits since car tours of the Skagit, Okanogan and Stehekin Valleys are enticing for color and wildlife during the less busy "shoulder seasons". Day hikes are excellent and give a great taste of the wilderness, whenever the weather is good. Storms are common: always be prepared for a few days of rain and wind. Warm, waterproof clothing and a tent are necessary for spring, fall and winter trips into the backcountry. Heavy snow and rain, at high elevations, characterize the North Cascades every winter. Avalanches are common in winter and spring in these steep mountains and even in places along the North Cascades Highway.

The east side of the Cascade Mountains (such as Stehekin in Lake Chelan National Recreation Area) is drier and warmer in the summer than the west side. Summer temperatures at Stehekin reach the 90's F. Winter at Stehekin and at all elevations above 2,000' throughout the park complex may be snow covered from late fall into spring.