2011 Spring Peak: Follow the mid-June Merced River flow prediction. 

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General Data

• CA Dept. of Water Resources Data Exchange Center 
• USGS National Water Information System 
• NPS Water Resources Division

Happy 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.

• Merced River above Pohono Bridge gage
• Merced River above Happy Isles gage
• South Fork Merced River at Wawona gage
• Near real-time streamflow data of the Merced River: Hydrographs of hourly stage height and discharge at four locations in the past 24 hours.

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.

• Tuolumne River at Grand Canyon of the Tuolumne gage
• Tuolumne River near Hetch Hetchy gage

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

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

• Yosemite weather & road updates: Call 209/372-0200 & press 1
• Yosemite air quality and smoke monitoring data, including near real-time ozone and particulate matter levels
  

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

• National NPS hydrology webpage
• National NPS climate change webpage (by the Climate Change Response Program)
• Read the 2010 NPS Climate Change Response Strategy's integrated elements: science, adaptation, mitigation, & communication [5.2 MB PDF]
• Read a 2009 White House climate change report [13.4 MB PDF]
• Learn more about RAWS (Remote Automatic Weather Stations) weather station network. [159 kb PDF]
• See a 2009 Park Science article on climate change's affect on the water supply by the park's hydrologist. [955 kb PDF]
• View a fuller list of hydrology references
  

Yosemite-based Hydrology Videos

These Yosemite-produced videos explore water-related topics:

• Hydrologist: Study the Scientist
• Glaciers: Yosemite Nature Notes
  
• Frazil Ice: Yosemite Nature Notes
  
• Yosemite Falls: Yosemite Nature Notes
• Horsetail Fall: Yosemite Nature Notes
  
• Snow: Yosemite Nature Notes
• Tracking the Snowline: Yosemite Nature Notes
• The Tuolumne Wild and Scenic River: Yosemite Nature Notes
• Floods of 1996 and 1997: Yosemite Presents
  

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.