Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The danger will rise to MODERATE as the day warms up. Both natural and human-triggered wet avalanches will become possible on steep slopes that face the sun. Pay attention to the surface conditions—avoid slopes where you're sinking into a wet, mushy snowpack. Generally safe avalanche conditions exist on slopes that are shaded from the sun.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    The likelihood of both natural and human-triggered wet avalanches will increase on sunny slopes as the day heats up. A number of wet slides occurred Wednesday and Thursday, but yesterday's cooler temps kept things quieter. Wet slides have been relatively small, but a few larger ones gouged down to the ground where the snowpack is thin, weak, and sugary. 

    Clear skies and cold temperatures overnight will have frozen the snowpack, but warming temperatures and sunshine today will quickly thaw the snow surface. Wet slides are most likely where you can check these boxes:

    • Slopes that directly face the sun, especially those with exposed rocks.
    • Where the snowpack is shallow and weak (less than about 3 feet deep).
    • Terrain sheltered from the wind.

    Your mission, if you choose to accept it, is to gauge how quickly the snowpack is melting through the day. Pay close attention to how deep the wet mush is becoming on the snowpack surface. If you're sinking into slush past your boot tops, or if your boards or sled are punching deep into the snowpack, it's time to head for colder (or gentler) slopes.  

    (2/10/2022) These wet snow avalanches likely occurred on February 9th, when a night of above freezing temperatures was followed by a very warm, steamy day. The failed on a SW-facing slope at 6,500-6,800'.

Avalanche Discussion

With a warm weekend ahead, it's time to remind ourselves about wet snow avalanches. As if the snowpack isn't complex enough, adding liquid water takes it to another level entirely. Did you know that water is the only material on earth that can exist at all three phases (liquid, solid, vapor) at atmospheric conditions? 

As warming temperatures, and especially the sun, add energy to the snowpack surface, it begins to melt and produce liquid water. This water melts the bonds that hold the snow grains together, weakening the snow. The more water that exists, the weaker the snow is. If the melt continues, the snow can become a saturated, soggy mess—think 7-11 Slurpee®. Rocks, being darker in color, absorb even more energy from the sun and can transfer that to the snowpack. That's why the snow can be even wetter around rocks, and these outcrops often are the origination point for natural wet slides. 

When the snowpack is deeper and relatively strong, mushy wet snow is often confined to the snowpack surface. The wet surface layer can peel away, either naturally or beneath our board and machine, but the resulting wet slide tends to be fairly small. But when the snowpack is shallow, weak, and faceted, it doesn't take much to make the entire snowpack a hot, soggy mess. Wet slides that occur in these conditions often gouge down to the ground and can entrain large amounts of snow. We've seen a few slides like this at lower elevations where the recent prolonged dry spell has left us with a shallow stack of sugary facets.

For all its complexity, wet snow problems can often be easier to manage. You can avoid the problem altogether by sticking to cold, shady terrain and avoiding traveling on or beneath steep sunny slopes. Timing plays an important role—if you plan to travel on sunny terrain, do it earlier in the day before things heat up. Finally, pay attention to how wet the snow surface is getting. If the slush is getting deeper than about 6-8", it's time to header for colder or less steep terrain. If you find yourself punching through the surface layers deep into soggy snow, you've overstayed your welcome and it's time to go somewhere else—pronto! 

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