St. Moritz has two distinct seasons, separated by brief shoulder periods when the lifts are closed and the hotels half-empty. Winter runs from December to April, with peak season in January and February when the slopes are best and the White Turf festival fills the frozen lake with racegoers and polo crowds. Snow is reliable at altitude, and the Engadin's 300 days of sunshine per year mean you are more likely to burn than freeze on a clear January day.
Summer runs from late June to September and is genuinely pleasant — warm days, cool nights, and walking trails across terrain that in winter is buried under metres of snow. July and August bring music festivals and the Engadin valley's full hiking season. Spring (May–June) and autumn (October–November) are quiet: some hotels close, and the mood drops. Come in winter or summer; avoid the gaps.