Forecasting Water from Snow

Three photos snowing snowpack measurement
A snow measurement site sign in winter (left) and summer (center) and surveyors assembling  a snow sampling tube at the base of Lassen Peak.

California Department of Water Resources and PG&E

Four times a year, hydrographer Ted Baker plunges a tube up to 35 feet long into the Lassen Peak snowpack. Baker is the latest in a long line of surveyors who have been measuring and recording snow depth and water content in Lassen Volcanic National Park since 1930.

Even in his first winter season, Baker noticed some interesting variations in his 16 survey sites, known as snow courses, located throughout the Upper Feather River Watershed. Just south of Lassen Volcanic, the Mount Dyer snow course (7,100’) provides a good view of Lake Almanor and highlights the snow coverage contrast of higher and lower elevations. Further south, the Four Trees snow sensor site (5,150') receives significant amounts of precipitation. This relatively low elevation site often provides a visible marker of the transition from snow to rain on the landscape.

Lower Lassen Peak (8,250’), near Lake Helen, is Baker's most challenging snow course. Multiple ice layers make it difficult to push the sampling tube down to the ground. His deepest snow core in 2017, taken on April 1, was 25 feet deep. Even with a partner, completing the ten measurements spread across the 1,000-foot course can take anywhere from two to four hours to complete, while other snow courses average about 45 minutes.

The snow survey process and equipment used by Baker is similar to that designed by James E. Church in 1905. Known as the Father of Snow Surveying, this unlikely liberal arts professor established the first weather observatory on nearby Mt. Rose. The station, perched between Reno and Lake Tahoe, served as an outdoor laboratory to study snow in all of its phases.

The resulting data exposed a link between water content of snow on Mt. Rose and the spring rise of Lake Tahoe. Church realized that by measuring the depth and the weight of a snow sample, he could determine the amount of water contained in the snow. This information was used to end a Lake Tahoe water battle between local land owners and downstream users by providing a forecast to inform water management practices.

Today, Church's methods are used at more than 300 snow courses throughout California. The multiple snow cores taken at each site tell a story of the storms that have come and gone. A light, powdery snow layer reflects a cold, drier storm; while a heavy, thick snow layer indicates a warmer, wetter storm.

In the winter of 2016-2017, visitors to Lassen Volcanic and nearby residents experienced more rain than in previous years. The wet weather was reflected in the density of Lassen Peak’s snowpack, which on April 1 measured 55 percent, the highest on record for the site. More than half of the 253 inches of snow on Lassen Peak was water. If all that snow melted instantaneously, it would create a pool of water 134 inches, or about 11 feet, deep.

Data from the Lower Lassen Peak snow course is used to produce monthly forecasts from January to May. Forecasters use average density and depth for each snowpack to estimate spring and summer snowmelt runoff into rivers and reservoirs. The April 1 measurements are generally the most significant as this is when the snowpack is normally at its greatest depth and density.

Snow water equivalent forecasts provide valuable information for recreation, agriculture, flood management, and hydroelectric power generation. Companies, like Pacific Gas and Electric Company (PG&E) in northern California, use the forecasts to determine what percentage of their electric energy generation will be hydro power. Water storage managers determine how much water can be safely stored in a reservoir while reserving space for predicted inflows, like snowmelt and rainfall.

Many of the organizations that use these monthly forecasts also contribute to them. Today in California, more than 50 state, national, and private agencies pool their efforts in collecting snow data. At Lassen Volcanic, park staff and partners work together to record data at Manzanita Lake and Lassen Peak. Visitors to the Lake Helen picnic area may have spotted the 36-foot-tall snow sensor that collects and transmits real-time data to specialists at the California Department of Water Resources. Data from this remote station is manually verified four times each winter by a surveyor, like PG&E hydrographer Ted Baker.

This winter Baker will return to the snow-covered slopes of Lassen Peak and collect snow measurements for the course. We will yet again anticipate the April 1 measurements, which will predict whether snowpack run-off levels will be high or low. Will a dense snowpack once again maintain normal reservoir levels restored last winter?

California’s precipitation is the most variable in the nation, making forecasting a particular challenge. Numerous years of data across hundreds of sites provide a valuable record of weather and the longer-term pattern of climate. The 2011-2016 California drought highlighted the importance of our mountain snowpacks, just as the water-rich winter of 2016-2017 focused our attention on water storage systems.

The data from the snowpack in Lassen Volcanic National Park may be almost as valuable as the water it contains. You can join the effort to collect and record data in the park or even in your own neighborhood. It may sound hard, but measuring precipitation in your backyard or calculating snow density is surprisingly easy. Although, just to make it a little easier, hydrographer Ted Baker recommends starting with a sample a tad smaller than a 25-foot-deep core.
A graphic depicting snow depth records
Three photos showing snow course measurement
Left to right: An orange marker at the Lower Lassen Peak snow course site, a surveyor assembles a sampling set, surveyors weight a snow-filled tube.

California Department of Water Resources

Measuring a Snow Course

California's 300-plus sample sites, known as snow courses, are visited at least once by a snow surveyor for data gathering. Two to six courses are measured in a day, depending upon how severe the weather is and how the snow surveyor travels to the site.

  1. Assemble snow sampling set consisting of aluminum tubes about 1.5 inches in diameter and 30 inches long. The bottom tube has a sharpened steel cutter section to cut down through the ice layers within the snowpack.
  2. Use a tape measure to locate the first of 10 measurement locations within the 1,000-foot snow course.
  3. Plunge the snow tube through the snowpack. Use the graduations on the side of the tube to read the snow depth.
  4. Place a single snow-filled tube containing a sample of the snow core on a scale. Record the weight of the tube and core and then the weight of the empty tube. These measurements are used to calculate how much water is in the snow.
  5. Disassemble the tubes once all 10 measurements are complete.

Last updated: March 19, 2019