Summer weather has arrived to Yosemite Valley. So have the people.

This year is the park’s 150th anniversary year. Many believe the park will attract more than 4 million visitors in 2014, with the majority of those arriving from now through September.

Ranger Kari Cobb, in anticipation of high visitor numbers in the next four months, provided the following guidelines:

Plan trips during the mid-week: Yosemite Valley is most popular on weekends and holidays which can mean traffic congestion. Fewer visitors arrive Monday through Friday.

Arrive before 10 a.m.: Most vehicle congestion occurs during the middle of the day. If you are planning a trip to Yosemite, arrive as early as possible.

Take YART’s: YART’s is the Yosemite Area Regional Transportation System (www.yarts.com). YART’s picks up passengers at multiple locations along Highway 140 (from Merced) and along Highway 120 (from Sonora and Mammoth Lakes). YART’s buses provide multiple drop-off locations throughout the park and in Yosemite Valley. Once visitors are in Yosemite Valley, they can enjoy the free shuttle throughout the valley, utilize the bike rentals, or simply walk, to enjoy many of park’s most famous sites and destinations.

Visit the Yosemite region: Groveland, Mariposa, Mono County, and Oakhurst all provide great lodging and visitor services that augment the Yosemite regional experience. Yosemite National Park Rangers join visitor bureau staff in these gateway communities to answer questions and provide advice and latest roadway information for Yosemite-bound visitors.

Explore more of Yosemite: Yosemite National Park is a big and there are many incredible sites and destinations outside of the valley. Visitors can explore such areas as Hetch Hetchy, Tuolumne Grove, Merced Grove, Tuolumne Meadows, and Wawona.

Other general tips on visiting Yosemite include:

If you want to camp, arrive early: Most campgrounds in Yosemite Valley during the summer are filled via the reservation permit system. There are, however, a very limited number of first-come, first-served campsites available throughout the park and visitors should arrive early if they would like to get campsite in these locations.

All trails within Yosemite are open: During the busy summer season, hikers are urged to pick trails outside of Yosemite Valley and explore lesser known parts of the park. Hikers should be aware that spring weather can be unpredictable and change without warming. Visitors are also urged to take special precaution around water, both lakes and stream-crossings.

Roads: All roads, including the Glacier Point Road and the Tioga Road, are open for the season. Campgrounds and services along the Tioga corridor will be opening in the coming weeks. Visitors traveling on these roads are urged to do so early in the morning or late in the evening when peak traffic has diminished. The Mariposa Grove Road leading to the giant sequoias is open for the season. However, the parking-lot normally fills in the morning hours and visitors should plan to take a free shuttle bus from Wawona.

Slow for bears: Park visitors are urged to drive slowly as animals are active and may be present on the roadway.

Tom Stienstra is The San Francisco Chronicle’s outdoors writer. E-mail: tstienstra@sfchronicle.com. Twitter: @StienstraTom

What sets you free? Hike. Bike. Camp. Fish. Boat. Wildlife watch. Explore.