Fog Forecast for North Cascades

The North Cascades are one of the cloudiest mountain ranges in the contiguous United States, receiving heavy maritime moisture from the Pacific that frequently condenses as valley fog, orographic cloud, and hanging mist. The Skagit River valley, which bisects the park along Highway 20, funnels moisture-laden air east from Puget Sound and produces some of the most dramatic fog conditions in the range. At the right elevation in autumn, fog fills the valley floor while glacier-capped peaks emerge above the cloud layer.

Diablo Lake and the overlook above it are among the best fog photography positions in the park. When low cloud sits in the Skagit valley and the turquoise water of Diablo Lake is partially obscured by moving mist, the scene is unlike anything else in the Pacific Northwest. The Cascade Pass trail in late autumn occasionally offers views above a fog layer filling the Stehekin valley to the east. Fall, from September through November, is the prime season for this kind of dramatic valley fog.

North Cascades fog differs from classic radiation fog — much of it is orographic cloud driven by incoming weather systems rather than overnight cooling. Watch for stable, moist air masses moving in from the southwest after rain events. The day after a frontal passage, when skies partially clear but humidity stays high, often produces the most photogenic broken cloud and fog conditions.

Humidity alone isn't enough. Wind alone isn't enough. Cloud cover alone isn't enough. Photogenic valley fog requires several conditions to line up at once, and most weather apps don't read them together.