Weather patterns in the Swiss Alps can be notoriously unpredictable, especially in the Bernese Oberland, and on average years snow lingers in the higher passes from winter storms until at least mid-June. The weather can be fickle in the Alps and August tends to be a wet month. Although you can start the APR from mid-late summer, generally the best time to start your trek is early-mid September where the sun can shine bright during the days but the nights and early mornings are cool. October is also a fine month but you can encounter some colder temperatures and snow in November. Trails in the Winter months can be impassible and you will also run the risk of being caught in or triggering an avalanche.