Yosemite Weather in August

August is the hottest month of the year in Yosemite Valley, and it lands in the thick of summer's peak season. Expect long, sunny days, warm afternoons, and a park running at full capacity, with Half Dome permits, high-country trails, and Tioga Road all in play. This is also the month when the park's famous waterfalls start running thin, so August is a season built around granite, alpine lakes, and the high country rather than roaring cascades. It's a reliable month for weather, just not a quiet one — plan around the crowds as much as the heat.

Yosemite Valley runs hot in August, with average highs around 89°F and lows near 55°F. Rain is rare, averaging just 0.4 inches for the month, and there's no snow to speak of, with roughly 13.7 hours of daylight to work with each day. The Valley floor sits at about 4,000 feet, and it's a different story up in Tuolumne Meadows at roughly 8,600 feet, where temperatures run 20 to 30°F cooler than the Valley floor. That gap matters most on any hike that climbs significantly, like Half Dome or Clouds Rest, where you can start in Valley heat and finish in high-country chill.

August keeps Yosemite's crowd level at its highest point of the year, still peak season even as summer starts to wind down. Roughly three-quarters of the park's annual visitors arrive between May and September, and Valley parking lots routinely fill by mid-morning on summer weekends and holidays. Trailheads for popular hikes fill early too, so plan to be moving well before sunrise if you want your pick of parking. The one thing that has changed since June is water: the waterfalls that roared in spring are thinning out by August, so don't plan an August trip around chasing big cascades.

Both Tioga Road and Glacier Point Road are open for the season, so the high country around Tuolumne Meadows is fully in play, prime time for high-country hiking with cooler air and long daylight hours to work with. Half Dome's cables are up too, though a permit is required and conditions should be checked before you commit to the climb. Down in the Valley, the Merced River is the move on a hot afternoon, swimming is one of the better ways to cool off once temperatures climb into the high 80s. Clear August nights are also excellent for stargazing, especially once you get above the Valley haze and into the high country.

Sun protection is non-negotiable in August, a hat, sunglasses, and SPF 50+ will do more for your day than almost anything else you pack, especially with highs pushing 89°F on the Valley floor. Carry plenty of water and refill often. If your plans include the high country, pack layers, temperatures swing hard between a hot Valley morning and a cool Tuolumne Meadows afternoon, and evenings up there drop well below Valley lows near 55°F. Heading into the backcountry overnight means a bear canister is required, and if the Merced River is on your list, water shoes make the rocky riverbed a lot more comfortable underfoot.

Tioga Road and Glacier Point Road are both open in August, giving full access to Tuolumne Meadows, Olmsted Point, and the high country beyond. The main hazard this time of year is timing: afternoon thunderstorms build quickly over Tuolumne Meadows, Clouds Rest, and the exposed granite domes, so plan to be off high points and summits before storms typically develop in the afternoon. The Half Dome cables become genuinely dangerous in wet or stormy conditions, and fatalities have occurred there, so check the forecast before you commit to the climb, and turn back if storms are building. Above 8,000 feet around Tuolumne Meadows and Tioga Pass, sun exposure is stronger and altitude can bring on headache or fatigue, so acclimatize gradually and add extra sun protection at elevation.