Upper Yosemite Falls has a longer season than some of the falls in the valley, but its peak still arrives closer to May.
WONDERFUL WATER: Being a visitor to Yosemite National Park in September or October can have its pleasures. Nights are cooling down and crowds are dispersing and a leaf here and there might be looking rather golden. But the famous valley's famous waterfalls? It's not their time of year. They rely on snowmelt, and snowmelt of course follows winter, meaning that springtime is the right time to see the falls in all of their powerful, rainbow-making, foam-dispersing glory. It's true that some of wonders around the valley, keep a more year-round schedule -- and Horsetail Fall starts to do its thing in December -- but a waterfall enthusiast cannot go wrong arriving in March or April (emphasis on April). Lots of other people will be there to admire the park's H20-ness during the spring, but it's a different vibe than summer, a bit more chill (to go with the temps, which are still a bit chill).
WHAT TO LOOK FOR: As mentioned, Horsetail Fall gets an early start but it has an earlier finish, too, in April. But Sentinal Falls and Ribbon Falls churn up around March, running through into the first part of summer. Yosemite Falls, which has both an Upper and Lower fall, has a longer run with a fall start, but its peak comes close to May. You can also eye what water runs all year, and where to see it.
STAYING OVER: There are a number of choices in and near the valley, including the historic Ahwahnee and Yosemite Lodge at the Falls, which, as its name suggests, is falls-adjacent. Just remember wherever you go, and wherever you stay, and whatever you do, that it is best to let nature be, even the smallest of sticks.