Protect and Enjoy: Snow Science and the Ever-Changing Winter Landscape
Cross-country skiing in Lower Carpenter Valley, photo by Julie Munger.
As we explored last year, the Land Trust’s protected properties have been sculpted into dramatic landscapes by millions of years of geologic forces, leaving the mountains, ridges, canyons, and lakes we all enjoy today.
In the winter months, similar forces play out on a much smaller timescale, shaping and re-shaping a blank white canvas of snow. Temperature, sun, wind, and water all play a role, and a wintery Land Trust property can look completely different from one day to the next. This not only makes winter a beautiful time to explore Land Trust lands, but also warrants some safety precautions for backcountry travelers as well.
At the forefront of the science in understanding the ever-changing snowpack, and how to safely navigate it, are the forecasters and observers at the Sierra Avalanche Center. David Reichel, a professional observer with and executive director for the center, has been working around wild snow for the last couple of decades.
And for Reichel, the story starts with a snowflake.
“Snowflakes fall from the sky – these beautiful, mostly unique flakes hit the ground and begin to change,” Reichel said. “If we’re in a proper winter with temperatures below freezing, those flakes change to either rounds or facets. If we have a deeper snowpack with more moderate temperatures, they become rounds, which generally form strong bonds, making a stronger snowpack. If temperatures are colder and the snowpack is shallower, they’ll change to facets, or what some people call sugar snow – angular and resistant to bonding with their neighbors.”
Now that we’re on the ground, part of a snowpack as either rounds or facets, a number of other forces come into play, including sun, ambient temperature, subsequent snowfall, and wind.
In the mid-winter months, winds preceding and during storms can routinely top 100 miles per hour over ridges.
“Those winds can redistribute a ton of snow – scouring one area and redistributing two or three feet of snow in another area,” Reichel said.
A wind-created cornice in Johnson Canyon, photo from the Sierra Avalanche Center.
Wind lips, cornices and sastrugi – long ridge-like patterns in the snow – can form along with wind slabs, one concern for backcountry travelers in avalanche terrain. And as new snow falls on top of the old snowpack that’s transformed over time, these instabilities can be buried deep – making them harder to detect and more risky, he said.
While short days and low sun angles reduce the effect of solar rays and temperatures in the winter, things begin to change in the spring.
“As conditions get above freezing, we can start to see straight water in portions of the surface of the snowpack, and we get what’s called wet metamorphism, as opposed to cold metamorphism, with a freeze-thaw cycle happening over time,” Reichel said.
When those conditions line up correctly, we get a Sierra backcountry skier’s favorite – called corn snow – but when the scales tip too warmly – wet loose avalanches become a concern.
Sun cups on Donner Summit, photo from the Sierra Avalanche Center.
An additional spring snow sculpture many Sierra enthusiasts are familiar with are sun cups. A scalloped pattern of bowl-shaped depressions in the snow, often described like a honeycomb. They are formed by sun melting the snow, often around dirt or debris that act like the grain of sand at the center of a pearl.
“Nature is infinitely complex. We can get a weird random warmup event, a melt crust or rain crust, then get a new storm that buries that crust, and then get faceting near that crust or some near-surface faceting,” Reichel said.
For those who want to get out and see these winter wonderlands firsthand, it’s important to consider your experience, the terrain, and current conditions as they pertain to safety.
To get an idea of how varied and intricate snow conditions can be, we’ll take a look at three Land Trust properties – all close to one another – presenting different conditions and recreation opportunities on snow. Each offers a unique winter experience, and each requires a different level of avalanche education and experience to enjoy.
First up, Donner Summit Canyon, to the west of Donner Lake, is popular with snowshoers and dog walkers, with relatively flat terrain. The walk gives gorgeous views of Donner Peak, Black Wall, and Donner Lake.
“One of the major things to focus on for avalanche risk is slope angle – generally think of steeper than 30 degrees (roughly comparable to a blue square ski run) – any time you’re on that type of terrain you’re in avalanche terrain,” Reichel said.
And while the popular routes in Donner Summit Canyon don’t have those kinds of slopes, it’s important to be aware that those slopes can be above you if you get under Donner Peak or the slopes beneath Old Highway 40.
Johnson Canyon on the other side of Interstate 80 is also popular with winter recreation – including relatively flat terrain near the parking area safe for general snow play, and more complex terrain higher up the canyon.
“Elevation matters a lot for snow depth, and conditions can change quickly as you travel up Johnson Canyon,” Reichel said.
And just a little farther west up on the crest, Frog Lake and the newly opened Frog Lake Backcountry Huts presents the most complex terrain for snowpack of the three.
“Frog has steep terrain wrapped more than half-way around it, which is consequential,” Reichel said. “There can be a lot of wind loading and cornices, so travelers need to consider those types of risks.”
This article is in no way a substitute for proper avalanche education for those interested in exploring Land Trust lands in the winter. The Sierra Avalanche Center offers numerous resources, including daily avalanche forecasts, along with links to avalanche education programs, for those wanting to learn more. The center is a partnership between the nonprofit and the US Forest Service and is critical for all backcountry travelers who rely on those daily forecasts. Learn more here.