Sunriver draws visitors year-round for different reasons. Summer — late June through September — is peak season. The weather is warm and dry, the bike paths are busy, the river is floatable, and the observatory runs its public viewing programmes most nights. Crowds are real in July and August; rental prices reflect this. If you want the summer activities without the full-price crush, late June and mid-September are good compromises.
Winter brings skiers who use Sunriver as a base for Mount Bachelor, 20 miles to the northwest. The slopes are usually good from late November through March, and resort prices drop significantly from the summer peak. Snow in Sunriver itself is light and infrequent at elevation — the resort is at about 1,300 metres, lower than the ski area — so the village stays accessible even in cold snaps.
Spring and autumn are quiet and often lovely. The ponderosa forest turns a warm amber in October. The observatory is open on weekends. The river is too cold to float comfortably, but fishing is good. If you are coming specifically for hiking in the Deschutes National Forest, the shoulder seasons have cooler temperatures and fewer people on the trails.