Sun Valley Avalanche Bulletin

This bulletin is from the Sawtooth National Forest Avalanche Center in Idaho.

Sawtooth National Forest Avalanche Advisory

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The following bulletin was the last for the season and has some useful generic information on spring avalanches. To learn more about spring avalanches check out our Spring and Summer Avalanche Dangers page in the Education Center.

This is Chris Lundy with the Sawtooth National Forest Avalanche Center with our last advisory of the season on Monday, April 7, 2008.

Avalanche Conditions: Spring has not really arrived at upper elevations where a cold, winter-like snowpack remains. This means youll want to continue to treat the snowpack like you would mid-winter, looking for potential weak layers and evaluating the stability of those layers.

Another concern will be when spring does finally arrive in earnest.

When the spring-time heat inevitably turns on, watch out for periods when overnight temperatures remain above freezing, especially if this lasts for a few days or more. Under these conditions, our upper elevation snowpack may go isothermal which is a fancy way of saying that liquid water is present throughout the entire snowpack. The first time this happens in the spring, it comes as quite a shock to the snowpack and can lead to unstable conditions and large, dangerous wet avalanches. Once the snowpack figures out what to do with the liquid water, the snowpack tends to become more stable, especially with overnight temperatures below freezing.

Intensive warming often makes cornices more susceptible to breaking off, especially with the added weight of a person. They may break back much further and wider than you anticipate. Cornices are quite large this year from all of our wind events.

Below are some avalanche safety tips for spring backcountry sliding and riding.

Timing: Get out early, follow the sun as slopes heat up and be home by early afternoon. There's great snow conditions to be had, but stay heads up in alpine areas and at upper elevations where the snowpack may be more winter-like.

New Snow: New snow will be more sensitive to the suns heating than older snow. Spring temperatures and sunshine are intense and will initially decrease the stability of any new snowfall on steeper slopes.

Watch for newly formed wind slabs on crusty layers or lighter density snow. It is still important to dig down and see just how well the snow layers are bonded together, how wet or how weak the underlying snowpack may be.

Temperatures: Pay close attention to how deep the overnight freezes penetrate the snowpack. Watch for spring rain events or a dramatic warm-up, either of which lead to increased avalanche danger. Clear skies help to promote a good freeze, clouds create a greenhouse warming effect.

Safe Travel Practices: We continue to recommend safe travel practices such as one person exposed on a slope at a time, closely watch each other, carry avalanche beacons, probes and shovels and be well practiced with them.

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Reported Conditions

[These open in a new window]

• Titus Peak, Idaho, 10,080'
• Lower Titus Study Plot Idaho
• Sun Valley Bald Mountain, 9000'

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