Hydrology and Climate Data Sources

Happy Isles webcamHappy Isles Gaging Station Webcam (provided by the USGS) of the Merced River. This Yosemite webcam is believed to be the first webcam view of a river in the National Park Service. When using the cam, you can zoom in or out.

Streamflow Data

Merced River: The Pohono and Happy Isles gages are on the main stem of the river, located in Yosemite Valley. The Wawona gage is on the South Fork of the Merced, near the southern boundary of Yosemite National Park. The Briceburg gage is on BLM land, downstream of the park and the confluence of the South Fork of the Merced.

Tuolumne River: The Tuolumne River at the Grand Canyon of the Tuolumne River gage is located just upstream of Hetch Hetchy Reservior. A second gage is located just downstream of O'Shaughnessy Dam.

Weather Data
Access weather data from stations in Yosemite National Park:

Dana Meadows
Gin Flat
Ostrander Lake
Tenaya Lake
Tioga Pass
Tuolumne Meadows
White Wolf
Yosemite Valley

Snow Data

  • See snow survey data from the most recent surveys in California. Snow surveys are performed four times per year at 13 courses with records dating back to 1931. Maximum snow depth at one of Yosemite's snow courses was 232.9 inches in 1969; maximum snow water content was 96 inches in 1983. Read the survey's 1953 history in a Yosemite Nature Notes article. [600 kb PDF]
  • California Cooperative Snow Survey's real-time data combines data from multiple agencies to monitor seasonal snowpack, forecast snowmelt runoff, and provide a central source of information about snow and water conditions in California. To see real-time snow data in the Yosemite area, navigate to the site, select the "Snowpack" tab at the top of the page, and then select "Tuolumne & Merced Rivers" in the box entitled "Snow Sensor Plots." In addition, most stations listed under the Weather section on this webpage have snowpack data also.
  • Compare this season's Sierra Nevada snow water content with the wettest year on record, the driest year on record, the mean value, and last year's value.
  • View a series of snow melt graphics of 2010's snow cover that represents a typical snow-cover year.

Resources and Further Reading

Yosemite-based Hydrology Videos

These Yosemite-produced videos explore water-related topics:


Volunteer: How to Get Involved: Volunteer in the park's water quality monitoring effort of the Merced River. Help collect water samples that will be tested for nitrate and phosphorous concentrations. Participate 8 a.m.-5 p.m. the first Wednesday of every month (except December and February). Call Katy Warner at 209/379-1421 to sign up.

Line chart of the river's water levels

In Yosemite, seasonal snowmelt creates high streamflow volumes in the springtime. The Merced River's annual peak for 2010 occurred on June 7, when mean daily discharge was 6,244 cubic feet per second. All snow melted from the sensors by June 20 but remained at higher elevations.

Winter landscape in High Sierra

Early spring melt in Tuolumne Meadows signals the onset of the spring pulse, which is a critical period for monitoring water-resource conditions.

Did You Know?