When is the best time to visit Yosemite? The answer will vary based on who a person speaks with, as well as what one's personal interests are. The following may help narrow down a "best" time of year based on schedules, interests, and itineraries.  Also, the National Park Service has put together a summary of seasonal conditions that may be helpful.

If at all possible, avoid visiting on the Saturday/Sunday of Memorial Day weekend (last weekend in May), 4th of July weekend, and Labor Day weekend.  To find out why, get a sense of the traffic from a TA article

Is it better to visit in the spring or the fall?  March qualifies as winter in the mountains, with storms, but Badger Pass ski area is still open and Yosemite Valley accessible.  In April, skiing is done, but Glacier Point Road/Tioga Roads are still closed, and many hiking trails still covered in snow. Waterfalls are there but not huge.  May brings big waterfalls and lots of water, and dogwood trees blooming right around Mother's Day weekend. Glacier Point and Tioga Roads are still usually closed for the season. This can start changing over at the very, very end of May, but it is highly weather/winter dependent.  Hiking (without good trail finding experience) is still generally limited to the Valley and Hetch Hetchy, as higher elevation trails are still covered in snow.  

September/October mean very small waterfalls, and not very many waterfalls.  Weekends are still crowded though not as bad as July/August. Usually all parts of the park are accessible by vehicle, though storms can result in temporary closures, and October is less dependable road wise than September. Great hiking is usually still available throughout most of the park.  Avoid Labor Day weekend, the first weekend in September.  Leaves in Yosemite Valley generally don't start changing color until the end of October, but this is hugely variable. Also, the color change isn't as dramatic as the eastern parts of the United States. Aspens in the higher elevations can start changing over in middle to late October as well. Just remember that Tioga Road can experience temporary (sometimes multi day) closures throughout October if cold storms roll in.  

To see waterfalls at their best, visit in late May to early June. Snowpack in the higher elevations will be melting, meaning waterfalls in Yosemite Valley and Hetch Hetchy will be close to peak.  When exactly the true peak occurs varies from year to year based on weather. However, visiting anytime during this window can pretty much guarantee impressive water.  These are also the good months for moonbow viewing during full moon time periods. Mirror Lake is largest at this point. There are disadvantages to this time period. Particularly in late May, but even into June, Glacier Point Road and particularly Tioga Roads may still be closed. Again, this depends on the weather and the snowfall of the preceding winter. It is key to have alternate plans if coming to Yosemite from the eastern side of the Sierra Nevada (Las Vegas, Reno, Death Valley). Also, even if Glacier Point Road and Tioga Road are open, some hiking trails may still be very difficult to find as they may still be covered in snow. This particularly applies to trails off of Tioga Road, but can also apply to Glacier Point Road.  Again, flexibility in high elevation hiking plans is key during this time.  Remember that Yosemite Falls is frequently dry any time from late July to late August (and into September), with other waterfalls diminishing significantly as well during this time.

To see as much of the park as possible by car, July through September will be the time to visit. Fairly consistently (though there are exceptions) all of the roads are open during these months. Both the lower and higher elevation areas of the park are generally accessible, with at least some, if not a ton, of hiking available. July 2011 saw some hiking still restricted by snow and very, very high water. However, this was an unusual year with lots of more snow than usual. July and August tend to be the busiest months of the year. If possible, avoid the park on Saturdays and Sundays. Weekdays are also very crowded, but traffic tends to peak on the weekends. If in the park on weekends, focus on the Tioga Road area to at least avoid some of the maddening traffic/parking, though there will still be plenty of people in that area.  2011 also saw June as unusually busy, with traffic similar to July levels.

To hike Half Dome, visit June through September.  Keep in mind that the Half Dome cables generally up the 3rd weekend in May, and stay up until Columbus Day in October, so technically the hike is do-able in that time range. However, late May can be very hit and miss as far as weather. In 2011 with the extra snowpack, cables did not go up until June.  Also, October is very much a transition time for weather. It is not uncommon for a snow storm or heavy rain storm to roll through in October, making Half Dome ascents treacherous.  Also remember obtain a Half Dome permit well in advance of visiting, as these are hard to come by when they become available, and nearly impossible to come by a day or two before a planned hike.  The National Park Service has a page about permits and there is a TA article as well. 

To avoid crowds and see waterfalls...this really isn't possible.  Visiting on weekdays in late May and avoiding Memorial Day weekend  will reduce the number of people/cars encountered, but there will still be plenty of people and most Yosemite first timers will still consider their visit crowded any time during waterfall season. 

To truly avoid the crowds, visit in December through March.  There are many caveats to this. Thanskgiving week, Christmas/New years time, and President's Day weekend can still be fairly busy and difficult to get lodging/camping reservations. For the most part though, these are the months where a person can stroll through Yosemite Valley and feel like they have the park to themselves.  Accessibility is more limited during these months. Glacier Point, Tioga Road, and the Mariposa Grove road are closed to traffic. Glacier Point and Tioga are only accessible to cross country skiers (and very hearty snowshoers), and they are long treks. The Mariposa Grove of Giant Sequoias can be accessed by foot, with a 2 mile gradually (but noticeably) uphill hike to the parking lot where trees are viewable. It's another uphill 1 mile to the Grizzly Giant.  Sometimes the road into the Grove is clear of snow, and therefore a relatively moderate walk since it's paved. It is not uncommon for it to be covered in snow, and this makes the walk in more difficult.  Tenaya Lodge usually rents snowshoes, and it is located about 10 minutes south of the Mariposa Grove on hwy 41. 

Yosemite Valley is still very accessible, though tire chains may be required depending on weather, particularly on hwy 41 or hwy 120, but sometimes on hwy 140 and in the Valley itself.  Views of Half Dome, El Capitan, Bridalveil Fall, Yosemite Falls, and Glacier Point are easy to access.  The 4 Mile trail is closed part of the way up, and even before that remains icy/snowy most of the winter because it is always in the shade.  Upper Yosemite Fall trail is frequently in very good condition, particularly to the first viewing area of the waterfall because the trail is in the sun every day. Lower Yosemite Fall is generally very accessible, though like the rest of the Valley, can be icy/slippery at times. The Mist Trail is closed because of rockfall danger and ice, but depending on temperatures, the footbridge to view Vernal Fall can be accessible. It is in the shaded part of the valley though, and because it is paved can get quite slippery.  Mirror Lake is very small at this point, but usually walkable.

There is also ice skating available during until early March, in Curry Village.  

 In 2013, the park put out a short video about visiting Yosemite in the winter. One interesting note, the video says that tire chains are rarely need on hwy 140. Tire chains are definitely less likely to be required, but it can happen. Additionally, hwy 140 may not require tire chains, but sometimes Yosemite Valley will.

Skiing, Snowshoeing and Snow Tubing

The Badger Pass Downhill Ski Area is open from mid December until the end of March weather permitting. Badger Pass is one of the old ski hills in California and is a family oriented area with an excellent ski school. Even if you do not ski the trip from the valley can be worthwhile. Badger Pass also offerssome of the best cross country skiing available with 90 miles of marked trails and 25 miles of machine groomed trails; especially good is 21 mile loop to Glacier Point, which is spectacular in winter.  There are also guided, backcountry cross country tours available.

You can also snowshoe at Badger Pass with either ranger led snowshoe walks or independent walks. 

Snow Tubing is the fourth activity at Badger Pass and happens with morning and afternoon sessions that last two hours each.

Badger Pass offer rentals for cross country, downhill ski/snowboard rentals, ski lessons, snowshoes and snow tubing.

A free bus runs from Yosemite Lodge to Badger Pass twice in the morning though it is possible to drive to Badger Pass independently (tire chains frequently required on the road).

To backpack, July through September are great months, though October can be too depending on the weather.  It is possible to backpack earlier in the year. However, unless prepared to trail find through snow, it can be very difficult. Add to this high water crossings, and then it becomes a bit more...exciting (read potentially dangerous depending on previous backpacking experience).  March through June, Hetch Hetchy is a lower elevation area popular with backpackers.  October 15th is a key date to keep in mind. From this point forward, no overnight parking is allowed on Tioga Road or Glacier Point road, because of the rising chance of snow storms that may close the roads for the season. This can put a crimp into backpacking plans in those areas.

Special Days and Events at Yosemite are held throughout the year. Here's a list of some:

 

  • Bracebridge Dinners are held during the Christmas season at the Ahwahnee Hotel. It is four-hour pageant of carols and entertainment remnicient of the Middle Ages. The Dinners are just part of the many holiday festivities held at the Ahwahnee. 
  • Special Culinary Events 
  • Full Moon Programs at Yosemite include ranger hikes/walks and night time tram tours. Check the newsletter for specific dates and times.
  • Free Park Days is exactly like what it sounds. Free admission Yosemite National Park. 
  • Earth Day (April 22) week-long activities include bike rides and special volunteer opportunites.
  • Apple Picking Day (mid August) helps the park get rid of wild apples so they don't attract bears. Check in July for exact dates when apples are ripe for picking.
  • Halloween Fun Night is typically held the last Saturday before Halloween in October. Kids have fun activities in the night and walk up a pathway lined with glowing carved pumpkins.