As a series of winter storms head toward the Sierra this weekend, an avalanche watch has been issued for the region’s backcountry starting Friday and lasting into Saturday morning.
The Sierra Avalanche Center has, in particular, termed the danger for Saturday “High,” saying that “wet loose snow could slide downhill, gathering more wet snow as it moves.” Updates to the avalanche watch beyond Saturday morning are likely given that high danger may persist through the weekend.
“Conditions will change quickly as this storm impacts the region,” warns the Center. “The same slope may go from only having a small amount of wind-blown snow in the morning to holding a wind slab large enough to bury a person while you have lunch.”
A year ago, a deadly avalanche at Palisades Tahoe Ski Resort in Olympic Valley claimed one life and injured another person, sending shockwaves through the Sierra ski and snowboard community. But avalanches within resort boundaries remain incredibly rare—especially fatal ones.
According to the Colorado Avalanche Information Center, which keeps detailed yearly records, only nine people have died in the last decade from avalanches within resort boundaries (known as “inbounds”). That’s out of the 232 who have died in total — most being people who were exploring the backcountry or ducking under barriers to go out of bounds at resorts.
If you’re planning on heading up to the mountains this winter, keep reading for what to know about avalanches — why they happen, how to prepare for the worst, and what to do if you’re caught in an avalanche yourself.
If you’re venturing into the backcountry — which means beyond the boundaries of a ski resort — then you need to take an avalanche safety course. This will give you far more detail in understanding avalanche conditions and rescue protocols.
If you’re planning to stay primarily in a resort or mountain park, then you should still know the basics — many of which you can learn through the National Avalanche Center’s free course videos and educational materials on avalanches.
The most important rule is not to venture into closed areas of the resort and not to “duck” under out-of-bounds ropes. Pay attention to any alerts or warnings.
The Sierra Avalanche Center has also created a daily flow guide for a simple way to understand the best practices when skiing and snowboarding in the Sierra. This includes:
Check, check, check the forecasts.
The Sierra Avalanche Center, along with a number of avalanche experts and offices around the West, puts out daily forecasts with predicted avalanche dangers and conditions to watch out for. They also put out weekly overall updates on the state of the snowpack.
However, reading an avalanche advisory in detail does require some background knowledge. If you plan to stay within the resorts, then the “bottom line” information (which is listed at the top) supplied in the advisory forecasts should give you the main takeaways.
A good rule is to pay attention to the warning signs that an avalanche could happen when you’re out in the snow. According to the Sierra Avalanche Center’s daily flow guide, these include:
There are different kinds of avalanches that come with different kinds of warning signs and frequency. The two main kinds are dry-loose or sluff avalanches — which are made up of soft snow that collects as it moves — and slab avalanches, which occur when a cohesive layer of snow breaks and moves as a slab downhill. The Palisades avalanches this week were believed to be slab avalanches.
The science of how snow layers form and break is complicated, but in essence, avalanches occur when there’s a surface bed of snow at the bottom, with a weaker layer of snow on top — and then new snow on top of that weaker layer. This creates conditions where the weaker layer can collapse, and the mass of snow on top can fracture and slide. While this can happen naturally, human activity almost always triggers avalanches, causing the weaker layer to collapse.
Things that can affect the likelihood of an avalanche occurring are, according to the National Snow and Ice Data Center (PDF): The instability of the snowpack, the recent weather and snowfall, and the terrain. Avalanches are most likely immediately after a large storm when there has been significant snowfall. Heavy wind that quickly blows in large amounts of snow on top of an existing layer can also cause dangerous conditions. Slight melting and refreezing each night can stabilize the snowpack — but extended periods of out-of-the-ordinary weather changes can cause instability. Even whether or not a slope faces the sun, and the steepness of that slope, can affect the probability of an avalanche.
Within resorts, ski patrols monitor these conditions and conduct avalanche controls — deliberately setting off small avalanches to keep the potential for larger ones from building up. In the backcountry, it’s important to be aware of all these changing variables since you won’t have ski patrols around to do it for you.
In the backcountry, avalanche equipment includes:
Many jackets and ski pants also now come with a RECCO reflector built in. This small transmitter looks like a label or tag on your coat, pants, helmet or backpack, which transmits to receivers operated by patrols or rescue crews. This is not considered a replacement for an avalanche beacon, but it can augment rescue efforts and is an easy add-on to have inbounds at a resort.
First and foremost, try to get off the slab or out of the oncoming avalanche track. This is, of course, not always easy to accomplish since avalanches can travel between 60 mph and 80 mph.
The Sierra Avalanche Center recommends two techniques for escaping the path of an avalanche:
The reason people die in avalanches is because the carbon dioxide in the area around their mouth, where they are buried, builds up. If they’re rescued within the first 15 minutes, there is a nearly 93% survival rate, according to stats published by the American Avalanche Association — but it drops drastically with every additional minute. This is why it’s crucial to take steps to increase the likelihood that you can be found and rescued quickly.
If you see someone caught in an avalanche, do not try to ski or snowmobile over to them while it is occurring — no matter how strong your instinct is to reach them to help out. Instead, you are likely to get caught in the avalanche yourself. You should try to note their starting position and where they end up, and then immediately start searching for them after the avalanche stops.
This story contains reporting by KQED’s Carly Severn. An earlier version of this story was originally published on Jan. 13, 2024.
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