Late spring through early autumn is the obvious time to visit. The Rogue is runnable from May to October, the weather is dry and warm, and the long Mediterranean-leaning summer brings the valley into its own. July and August are reliably hot — temperatures into the mid-30s Celsius are normal — and air conditioning is genuinely welcome.
Winters are mild compared to the rest of Oregon but the rafting season is over, and the days are short and grey. The shoulder seasons (May, September, early October) are arguably the best: warm enough to swim, cool enough to walk all day, and the salmon and steelhead runs are at their peak in early autumn.