Spring snow conditions can be deceptive. Backcountry users should exercise caution for avalanche safety during warming spring conditions. Photo: Avalanche Canada.
Spring brings the opportunity to travel higher and deeper into the backcountry. It's also a time of high activity from loose wet and wet slab avalanches. Now is a great time to have look at late-season snow conditions and be reminded of snowpack, weather and terrain conditions to consider when traveling through avalanche terrain.
Your local avalanche center website has the best information on what to look for in the specific zone where you're planning ongoing. Reading the avalanche advisory and staying current on snowpack structure, weather and temperature fluctuations is the best way to stay on top of, rather than being buried under, the snow during the spring riding season.
Photo by Forest Service snowmobile rangers in the Skyland area near Marias Pass, Montana.
Eric Knoff's timeless Spring in the Backcountry: A Look at Late Season Snow Conditions is a great review and applies to most high alpine areas. While spring riding can be the best, it can also hold avalanche hazards not encountered during the colder parts of winter. As snowpack and weather transition into a warmer and wetter spring pattern, there are a number of variables that influence snow stability. Pay attention to these:
- Terrain & Aspect: Typically, wet snow avalanches (primarily loose, wet avalanches) being earlier in the day on southerly aspects due to the impact of solar radiation. This type of instability then moves to east, west, and potentially north-facing slopes as the day progresses. Using different aspects to your advantage is a great way to enjoy spring riding conditions and avoid rising instability. However, changing aspect isn't always a sure-fire way to avoid unstable conditions. There are numerous factors that influence snowpack stability during the springtime.
- Temperature: As temperatures warm above freezing, surface layers of the snowpack begin to melt. If temperatures drop below freezing, this process is slowed, allowing the snowpack to adjust to these changes. However, if temperatures stay above freezing for an extended period of time (multiple days in a row), a large influx of free moving water can be introduced into the snowpack. This can create widespread instability and dangerous avalanche conditions. The first prolonged period of above freezing temperatures (both day and night) is a common time for spring avalanches to occur. If temperatures stay above freezing for an extended period of time, the snowpack can become isothermal. This is when the temperature of the entire snowpack reaches 32 degrees Fahrenheit (zero degrees Celsius). When the snowpack becomes isothermal, the structural integrity of the pack begins to break down, making wet snow avalanches likely. Typically during spring skiing, it's best to get an early start when the snowpack is frozen and stable and be off the slopes by the heat of the day.
- Wind: Wind can turn very safe snow into very dangerous snow in a matter of minutes. The wind is usually the most important weather factor in avalanche accidents. Wind erodes snow from the windward (upwind) side of obstacles, such as a ridge, and deposits the same snow on the leeward (downwind) terrain. Wind loading is a common denominator in most avalanche accidents. And it's no wonder because wind can deposit snow ten times more rapidly than snow falling from the sky. Moreover, wind-drifted snow is ground up by bouncing along the snow surface, and when it comes to rest it's often much denser than non-wind loaded snow. In other words, it not only adds significant weight on top of buried weak layers but it forms a slab that can propagate a fracture very easily. Cornices that have built up on the leeward sides of ridges over the winter tend to be very large by springtime and they can weaken with warming temps.
- Snowpack Structure: A major contributing factor to springtime avalanches, particularly wet slab avalanches, is the presence of buried persistent weak layers. Persistent weak layers (PWL) include depth hoar, surface hoar, and near-surface facets. The presence of PWL can produce dangerous avalanche conditions months after these layers form and get buried. Depth hoar (faceted snow near the ground) is the most notorious weak layer for producing large wet slab avalanches.
Fortunately, none of these PWLs exist in the snowpack this spring, at least in most of the Lower 48. But springtime avalanches still occur without buried PWL. A common avalanche during warm spring weather is wet loose avalanches or sluffs. This form of avalanche is typically less dangerous than wet slabs. However, wet loose avalanches can entrain large volumes of snow capable of carrying and sometimes burying a skier or rider. Wet loose avalanches generally start at a single point, but fan out as they move downhill. In steep terrain, wet loose avalanches can travel long distances and pick up significant volume and speed and send you into dangerous terrain features like cliffs, trees, and gullies. During the right conditions, this type of avalanche can also travel into a lower angle or flat terrain, where you might think you're safe. Wet snow avalanches in the spring typically occur during prolonged periods of warm and dry weather. This is generally the opposite of mid-winter avalanches which tend to occur after heavy periods of snowfall. If you're planning on spring riding, it's important to pay attention to changing snowpack and weather conditions.
Avalanche debris from slide triggered by split boarders on Mt. Parnassus on April 8, 2017. Photo: CAIC.
Reviewing avalanche incident reports will also give you insight and information as to what to expect when heading out into spring backcountry conditions. This CAIC Avalanche Incident Report, 4/8/2017 is a perfect example.
- BC Zone: Front Range
- Area Description: Mt Parnassus
- Weather Description: Moderate to Strong winds out of the west (but swirling all over in the basin), about 4C, Scattered.
- Avalanche Description: Today we (a group of 5) witnessed three split boarders skinning below and west of the Drainpipe on Parnassus shortly before noon. We then witnessed the slide but couldn't see if people were involved. Shortly after, it appeared from afar as if one of the friends made a quick rough beacon search on foot, and when he was about 20m out, he must have heard his friend because he b-lined it to where he began digging. We ripped off our skins and made our way down to assist. Three in our group headed down immediately (one is an EMT). By the time our three guys got there, the riders involved in the avalanche had located and extracted their buried friend. Two of us made a slower descent and took photos of the slide (after radio confirmation of successful recovery). Id says it was 5-10 minutes tops before the guy was fully out. The guy was nearly fully buried, head downhill, with only his face exposed and no injuries). The avalanche victim was wearing a Float pack, but did not deploy as the trigger was still stowed away. Another group in the area reported skiing the NE/E face and experienced solid conditions. Hmmm. Snowmachiners in the area high-marking on E/SE slopes. No issues.
A group of three splitboarders had been skinning up near a very pregnant wind-cross-loaded NE slope around 3600m. By their account, the first guy began to cross the slope and a couple of steps in it released and took him for about a 60m 80m ride. Looking across the crown of an unintentional human-triggered avalanche on Mt. Parnassus on April 8, 2017. Photo: CAIC.
Spring skiing can be some of the best of the season. Good snow coverage, warmer weather, and more predictable snow stability (at times) can lead to unmatched conditions. Please plan ahead, be cautious, and remember to practice THE FIVE BACKCOUNTRY BASICS get the gear, get the training, get the forecast, get the picture and get out of harm's way!