Using Weather Conditions to Predict Avalanches

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You may know well the importance of education, experience, knowledge, skills, and carrying the right tools when traveling in avalanche terrain.

However, it doesn’t matter how much rescue gear you have – you still need to know how to use it and how to interpret the data it provides. In addition, your decision-making processes can easily negate all of the data that analyzing the snowpack, weather, and terrain provides.

There are many well-qualified, knowledgeable snow science and avalanche professionals from whom you can take an avalanche course(s). Please only use the information contained in this blog as a brief refresher of information you already have or as a prompt to take a professional avalanche education course.

The past few weeks we’ve seen a shift in weather patterns throughout much of the lower 48 – everything from winter-like conditions to spring downpours. Many backcountry adventurers believe these changes equal a more stable snowpack. However, this is not always the case as my good friend, Eric Knoff, an avalanche forecaster for the Gallatin National Forest and Glacier National Park, and guide explains:

Spring in the mountains is a time of transition. The days get longer, the sun shines stronger, and the snowpack begins its conversion from frozen ice crystals to liquid water.

Though many choose to hang up their skis, spring can host some of the year’s best skiing. It isn’t uncommon to encounter soft powder and delicious corn in one descent. But, this isn’t always the case.

Moisture rich storms, dumping multiple feet of snow or saturating an entire snowpack with drenching rain can create dangerous avalanche conditions. During spring, both wet and dry snow avalanches occur. If the weather changes quickly, you can expect the snowpack to do the same. Depending on the snowpack, different weather events can produce different types of avalanches.

Above freezing temps, strong sunlight, and rain typically produce wet snow avalanches. These common avalanches occur when the snow surface weakens to the point of failure ­– essentially resembling a slushy moving down hill. Also known as point releases, they range in size from miniscule dribbles to freight trains of debris capable of snapping mature trees. They have a tendency to originate at a single point and fan outward as gravity takes hold.

A more dangerous and more unpredictable springtime avalanche, these typically occur when the snowpack is undergoing rapid change. The structure of the snowpack largely determines if a wet slab avalanche will occur. If a persistent weak layer such as depth hoar, surface hoar, or near surface facets exists in the snowpack, the probability of wet slab avalanches increases.

If temps are cold enough and snow falls, dry slab avalanches are possible. New snowfall, wind, and snowpack structure determine when and where these take place. Most dry slab avalanches occur during or immediately after a storm, so giving the snowpack a day or two of rest after fresh snow is a good rule of thumb.

Spring is an exciting time to be in the mountains. The snowpack and weather change constantly and avalanche hazards do the same. Paying close attention to changing conditions is the best way to avoid a surprise avalanche.

Play safe out there!

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