GNFAC Avalanche Advisory for Mon Apr 10, 2017

Not Current Advisory

This avalanche information bulletin is issued on April 10, 2017 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 an active time in the mountains. Weather and snow conditions can change quickly, and a range of weather produces a variety of avalanche problems. Here are some avalanche concerns to keep in mind:

(For more information on spring avalanche problems and travel advice see a couple recent videos from the end of this season (video 1, video 2), or this article.)

1. NEW SNOW AND WIND-LOADING

Spring storms are notorious for depositing heavy amounts of snow in the mountains. Fortunately, the snowpack throughout our advisory area is mostly stable, which will limit most avalanche activity to new snow instabilities if the mountains receive more snow. The main problems to look out for are avalanches breaking within 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 snowstorms. During spring conditions, dry snow instabilities tend to stabilize quickly, but it’s a good idea to give new snow a day to adjust before hitting big terrain.

New snow can quickly change from dry to wet on a spring day, and stability can decrease rapidly with above freezing temperatures or brief sunshine. New snow may bond well early in the morning, and then easily slide later. Anticipate changes in snow stability throughout the terrain and over the course of the day. An early start is always an advantage. Be ready to change plans or move to safer terrain at the first signs of decreasing stability, such as small roller balls or natural loose avalanches.

2. WET SNOW AVALANCHES

Spring and wet snow avalanches go hand-in-hand. Warmer temperatures and strong solar input (longer and more intense sunshine) can weaken the snowpack and increase wet avalanche activity. Conditions tend to become most unstable when temperatures stay above freezing for multiple days and nights in a row. During prolonged periods of above freezing temperatures, it’s best to avoid avalanche terrain. If temperatures drop below freezing at night conditions will stabilize during the morning hours and become increasingly unstable as the day heats up, necessitating an early, sometimes pre-dawn start to your backcountry adventure. 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 red flag. Wet snow avalanches, whether loose snow or wet slabs, can be powerful, destructive and very dangerous.

3. CORNICES

Cornices are huge and become increasingly unstable as the snow transitions from a cold winter pack to a warm, wetter snowpack. Cornices often lose strength during prolonged periods of above freezing temperatures. They can break off suddenly and farther back than one might expect. Give these massive chunks of snow a wide berth along the ridges, and 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.

4. 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.

Have a safe and fun spring and summer!

Doug, Eric, and Alex

 


MAY 4: Give Big Gallatin Valley

The Friends of the Avalanche Center are one of the recipients of the Give Big Gallatin Valley campaign. It is a 1-day fundraising event for local non-profits on May 4, so mark your calendars. The Friends will send reminders as the day approaches: https://www.givebiggv.org/organizations/friends-of-the-gallatin-national-forest-avalanche-center

MAY 20: SPRING SLED FEST in Cooke City

A fundraiser for the Friends of the Avalanche Center. $20 raffle tickets for sweet prizes; free BBQ on the mountain; raffle and party at Soda Butte Lodge 8 p.m. Check out the poster!

 


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