A partnership of the National Park Service and the United States Forest Service.

Sierra Nevada Snow Survey

  • Lincoln Else
  • Jan. 6, 2010

Water. It is one of the most important resources on earth and has played a central role in California’s history. How much of it will be flowing down the state’s rivers and streams each spring has long been a question of great interest. Answering that question means going to the source, and in California that means the Sierra Nevada wilderness.

California officials have been taking formal “snow surveys” in one form or another since the 1920s. While the science surrounding these surveys has become far more complex (and accurate) over the years, surprisingly many aspects of the surveys themselves have remained largely the same.

Each month throughout the winter, officials up and down the Sierra strap on skis and head into the backcountry. Armed with aluminum sampling equipment and prepared to brave the elements, their goal is to answer one simple question: how much water is in that snow? I recently teamed up with Yosemite Wilderness Manager Mark Marschall and Wilderness Specialist Mark Fincher on the “Falls Creek” snow survey in the Yosemite Wilderness to answer exactly that question.


Where's the snow? Yosemite National Park Wilderness Specialist Mark Fincher heading up switchbacks above Hetch Hetchy reservoir in March. Depending on the snow pack, many survey routes start on dry ground, requiring snow surveyors to carry their ski gear (in addition to survey equipment and survival gear) up the initial elevation gain.


Perfect blue bird - Mark Marschall, Yosemite's Wilderness Manager, working his way up the granite polished slabs above Lake Vernon under a clear winter sky. Depending on the year, snow can melt quickly on south facing granite faces making for a patchwork of granite and snow - slow going for the backcountry traveler.

The Falls Creek snow survey “courses” (sample locations) are all located deep in designated wilderness, so whenever possible Yosemite's rangers conduct the survey on foot instead of by helicopter. This is no easy task, requiring days of backcountry travel through rugged terrain. As Duane Jacobs, Yosemite’s Assistant Chief Ranger in 1953, said of Sierra snow surveys, “This work is truly a fertile field for proving the old axiom about separating the men from the boys. It also separates the fancy Dans of the packed slopes from the cross country travelers.”


Smooth Sailing. Mark Marschall glides up the Snow Creek drainage, traveling fast on snow still hard from the previous night.


Watch and learn, grasshopper. After reaching each snow survey site and finding the exact sample locations, the real challenge begins: getting an accurate snow sample. After years of survey work, Mark Fincher has mastered the "vertical javelin toss" required for the perfect tube insertion. It's all in the wrist. And the shoulder. And the forearms...


How deep is the snow? The first measurement is somewhat straightforward, though even this seemingly simple question can be hard to answer. Ice layers in the snow pack can fool the novice surveyor, and maintaining a clean good quality "core" throughout the process is no small challenge.


Wait for it.... wait for it.... Knowing there is ten feet of "snow" doesn't tell you all that much about the actual amount of water "in" that snow, known as the snow's "water content." To determine this key number, surveyors must carefully measure and weigh each snow core.


The star of the show. These snow "cores" are what surveyors use to determine water content in the snow pack.


It's all in the details. Mark Marschall carefully recording the depths and weights of each sample.


Crunching the numbers. So how much water is up there? Mark Fincher calculating the water content from the day's courses back at the snow survey cabin. This data will be sent to California water officials as soon as we get out of the backcountry. It will then be used to determine water predictions for the coming season.

On this survey we were lucky - good weather throughout and fantastic snow conditions made for fast backcountry travel. Unfortunately, this isn't always the case. Since snow survey's must be completed within a certain time window each month, surveyors often complete their work in the harshest of conditions (safety permitting).

The numbers gathered on this survey were quickly sent on to the California Department of Water Resources to be added to the hundreds of other measurement taken throughout the Sierra. Used together these measurements paint a complete picture of the Sierra snow pack.

Today, many of the snow measurements in the Sierra are taken by automated sensors (check out some of the links in the side bar for more info). These sensors help water officials build an even more accurate understanding of the regions snow pack, yet they are not (yet) a replacement for the old fashioned work of snow surveyors. Each month, dozens of dedicated men and woman will continue to strap on skies and head for another lap into the wilderness.


Onward. Mark Fincher makes his way through patchy snow fields on his way to the next snow survey location.