Summer (June to September) is overwhelmingly the main season. The lake is warm, the wineries are busy, and the desert scenery is at its most intense. July and August are the peak weeks — hot, crowded, and expensive. Osoyoos regularly records the highest summer temperatures in Canada, sometimes exceeding 40°C in July. The heat is dry and the evenings cool down significantly, which makes it tolerable.
Spring (April to May) is the best time for wildflower watching in the desert and for birdwatching during migration. The lake is too cold to swim, but the crowds are thin, the prices are low, and the landscape has a freshness that summer bakes away. This is when rattlesnakes emerge from hibernation — interesting for wildlife watchers, something to be aware of on trails.
Autumn (September to October) brings harvest season — wine grapes, apples, pears — and the valley has a mellow quality as the summer rush ends. The Okanagan wine harvest festival in early October is worth timing a visit around. Temperatures are pleasant and the colour on the hillside vineyards is good.
Winter is quiet. Most of the interest is in summer, and outside of ski trips to nearby Big White or Apex, there is little reason to visit in the cold months.