GNFAC Avalanche Advisory for Thu Apr 16, 2015

Not the Current Forecast

This avalanche information bulletin is issued on April 16, 2015 and does not expire. The Gallatin National Forest Avalanche Center has stopped issuing avalanche advisories for the season. Traveling in the backcountry requires careful snowpack evaluation. Avalanches don’t end until the snow melts.


Snowpack and Avalanche Discussion

Spring is a fickle time in the mountains. Weather and snow conditions can change quickly, producing a variety of avalanche problems. Here are some avalanche concerns to keep in mind:


Spring storms are notorious for depositing heavy amounts of snow in the mountains. Fortunately, the snowpack throughout our advisory area lacks buried persistent weak layers this season, which will help keep avalanche activity limited to new snow instabilities. The main problems to look out for are avalanches breaking under the new snow, wind slabs, and loose snow avalanches. Wind loaded slopes are especially dangerous and should be evaluated carefully before committing to steep terrain. Remember, the likelihood of triggering avalanches spikes during and immediately after significant snow storms. During spring conditions, new snow instabilities tend to stabilize quickly, but it’s a good idea to give new snow a day to adjust before hitting big terrain.


Spring and wet snow avalanches are synonymous. Warmer temperatures and strong solar input (increased sunshine) can weaken the snowpack and increase wet avalanche activity. Conditions tend to become most unstable when temperatures stay above freezing for multiple days in a row (including at night). During prolonged periods of above freezing temperatures, it’s best to avoid avalanche terrain and start and finish your day early. If temperatures drop below freezing at night, conditions usually stabilize during the morning hours and become increasingly unstable as the day heats up. Typically, wet snow avalanches start on east and south facing slopes and transition onto west and potentially north facing slopes as the day progresses. Be aware that sunny aspects may have a wet snow avalanche danger while shadier slopes still have a dry snow avalanche danger. Pinwheels and point releases are obvious signs of wet snow instability. Getting off of steep, sunny slopes should be considered when these signs are present. Also, punching to the ground in wet, unsupportable snow is a major red flag. Wet snow avalanches, whether loose snow or wet slabs, can be powerful, destructive and very dangerous.


Cornices become increasingly unstable as the snow transitions from a cold winter pack to a warmer, wetter snowpack. They often lose strength and become unstable during prolonged periods of above freezing temperatures. They can break off suddenly and farther back from the edge than one might expect. Give these massive chunks of snow a wide berth along the ridges. It’s also important to avoid traveling underneath large cornices as they can break naturally. Cornice falls can also entrain large amounts of loose snow or trigger slab avalanches. Regardless of whether a cornice triggers a slide or not, a falling cornice is dangerous to anyone in its path.


Yes, there’s always a disclaimer. It does not matter if new snow falls or not, avalanches will continue to occur until the existing snowpack is mostly gone. Always assess the slope you plan to ride with diligence and safety in mind. Do not let your guard down. Travel with a partner, carry rescue gear and only expose one person at a time in avalanche terrain. We live by these rules in winter and spring.

Have a safe and enjoyable spring and summer!

Doug, Mark and Eric


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