SW Montana Avalanche Bulletin

This bulletin is from the Gallatin National Forest Avalanche Center - [Map]

Gallatin National Forest Avalanche Advisory

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SPRINGTIME AVALANCHE INFORMATION

The Forest Service Avalanche Center is officially closed for the season and will not be doing anything again until next fall. If you head out, there are a few things worth keeping in mind with the snowpack.

Stability assessments are not always easy this time of year. A wide variety of conditions can be found and they can change by the hour. The snowpack is confused as it contains cold, dry snow and liquid water starts percolating through its layers. By late spring or early summer, this liquid water will have established channels in the snowpack. Under these condtions stability is very good, but the transition can be tricky. During this transition phase both dry snow and wet snow avalanches can occur, and we may see a wet slab avalanche cycle at some point. These avalanches are often large and destructive and can be very difficult to predict.

DRY SNOW AVALANCHE CONDITIONS

Faceted snow about 2 ft above the ground lingers in some areas and remains weak especially on high elevation, north facing slopes. This layer should not be overly active but I would watch out for it immediately following a storm that adds a sizable load to the snowpack. Give the snowpack time to adjust to this load before venturing into steep, rocky alpine terrain. Dig a snowpit at least 5-6 ft deep in a representative location. You’ll know you have found this layer if your shovel breaks through hard snow into loose, sugary, snow.

The other concern will be bonding between new snow and the old snow surface. Constant awareness of snow conditions under your skis or your track can give lots of information on this bonding if you’re paying attention. Quick hand pits can also yield valuable information and snowpits only need to be a few feet deep.

WET SNOW AVALANCHE CONDITIONS

On warm days with corn snow, timing is the key for good skiing and riding conditions as well as avalanche conditions. On a typical day the surface snow starts the day frozen and gradually softens as the sun and temperatures rise. This is the window for good skiing and riding. As the day progresses the snowpack will continue to heat up and avalanche conditions become more unstable. This is the time to head home. Signs of instability include sinking to your boot tops in wet snow and pinwheels of wet snow rolling downhill. Another sign of instability would be a dramatic rise in temperatures following generally cool weather.

Be especially cautious when the snowpack doesn’t refreeze overnight or only freezes the top inch or two of snow. Rain, warm temperatures overnight, and/or cloudy skies can prevent the snowpack from freezing. Clear skies and cool temperatures overnight help it freeze.

Lastly, basic avalanche safety applies even in spring. Travel one at a time in avalanche terrain and carry appropriate rescue gear.

Have a great summer and we’ll see you next fall!

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