Kamloops sits in the dry rain shadow east of the Coast Mountains and has the warmest, driest climate of any major BC city — over 2,000 hours of sunshine a year, summer highs often pushing 35°C, and winters that are cold and snowy but considerably less wet than the coast.
Summer (June–August) is the high season — long warm days, the rivers warm enough to swim in, music festivals and the Saturday farmers' market. Autumn (September–October) is the city's best-kept secret: 20–25°C, blue skies, the cottonwoods turning yellow along the river, and almost no crowds. Winter (December–March) is the time for Sun Peaks, which gets reliable dry powder snow from mid-December onwards. Spring (April–May) is short and unsettled — fine for hiking the dry hills, less so for swimming.
The smoke from regional wildfires can be heavy in late July and August in bad years; check air-quality forecasts before planning outdoor activity.