This avalanche information bulletin is issued on April 9, 2012 and does not expire. The Gallatin National Forest Avalanche Center has stopped issuing avalanche advisories for the season. Traveling in the backcountry requires carefully snowpack evaluation on the slopes you intend to ride or ski. Avalanches don’t end until the snow melts.
Some avalanche concerns to keep in mind:
1. WIDESPREAD INSTABILITY
The greatest avalanche concern is new snowfall and wind-loading. The likelihood of triggering avalanches spikes during and immediately after significant snow storms. Additionally, wind-loaded slopes are dangerous too. The good news is that any instability associated with the new and/or windblown snow can easily be found in the upper few feet of the snowpack. Instabilities associated with new snowfall will typically be short lived.
2. WEAK SNOW NEAR THE GROUND
Weak snow exists near the ground in many areas. This weak snow has been a problem all season and caused many avalanches. Triggering an avalanche on this layer will be hard to do, but its consequences would be severe.
This weak snow near the ground deserves some discussion. On high elevation N aspects, this layer is depth hoar and has changed little since it formed in November. On other slopes that experienced prolonged above freezing weather in late March, this depth hoar entered a transition period as it became wet. It produced massive wet slab avalanches in the Bridger Range. With recent cold weather, this transition period was put on hold as the percolation of liquid water through the snowpack stopped. Unfortunately this layer remains weak. Until we get prolonged warm weather to establish drainage channels for melt water through the snowpack, we should be concerned with this layer and remain conservative in our decision making.
4. WET SNOW AVALANCHES
Spring is synonymous with wet avalanches. As the sun climbs higher in the sky and daytime air temperatures stay above freezing, wet avalanche activity increases. More importantly, above freezing temperatures at night add to the danger and can create unstable conditions. South facing slopes get the brunt of incoming solar radiation, but the warming swings around to all aspects as spring progresses. Be aware that sunny aspects may have a wet snow danger while shadier slopes still have a dry snow avalanche danger. Pinwheels and large rollers of snow are a sign of increasing avalanche danger. Punching to the ground in wet, unsupportable snow is another bad sign. Wet avalanches, whether loose snow or slab, can be destructive and powerful.
5. DISCLAIMER
Yes, there’s always a disclaimer. If snowfall continues there’s a very real possibility that new weak layers will be buried created lingering, and possibly widespread instabilities. Always assess the slope you’re about to play on with diligence. Do not let your guard down. And always travel with a partner, carry rescue gear and only expose one person at a time to avalanche terrain. We live by these rules in the winter and they still apply in the spring.
Have a safe and enjoyable spring and summer!
Doug Chabot
Mark Staples
Eric Knoff