This is the advice that separates a good trip from a disappointing one, and almost nobody follows it.
April and May. Highest water of the year, off snowmelt and spring rain in the Blue Ridge. The commercial season opens on the gauge rather than on a fixed date, so an early-April booking can be moved at short notice. Water is cold, wetsuits may be advised, and the whitewater is the real thing. If you came for rapids, come now.
June. The transition month and often the sweet spot: water still moving, air warm enough to enjoy being wet, and the school-holiday crowds not yet at full strength.
July and August. Low, warm and slow. This is tube season, funyak season and family season, and it is when the local market has the most inventory. It is also the season of afternoon thunderstorms that build fast over the ridge and pull outfitters off the water at short notice.
September and October. The quiet half of the good weather. Air in the sixties and seventies, water still warm from summer, humidity broken, and colour coming onto the ridges from the middle of October. Fewer trips run as the season winds down, so book rather than turn up.
November to March. Commercially closed. The river is still there and it is not a beginner proposition.
Rain upstream changes everything within a day, in both directions. Ring the outfitter the morning of your trip rather than the week before.