Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

A prolonged warm-up and intense sunshine are turning the snowpack to mush. Dozens of wet avalanches occurred in the last two days and are likely to release naturally again today. Don't linger below large avalanche paths and avoid areas with wet, soggy snow. Triggering a slab avalanche large enough to bury a person would require a dose of bad luck but remains a possibility on middle and upper elevation slopes that did not slide during the earthquake.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2

    Yesterday I observed dozens of wet loose avalanches from the southern Sawtooths to Galena Pass and on into the Wood River Valley. For the most part, these avalanches involved thin layers of wet snow near the surface. With intense sunshine and even warmer temperatures today and tomorrow I expect wet avalanche activity to continue. The size and destructive potential of these slides may increase as meltwater pushes deeper into the snowpack.

    This problem is most likely:

    1. On steep upper elevation slopes that directly face the sun
    2. On slopes sheltered from the wind 
    3. On lower and middle elevation slopes regardless of the direction they face.

    Keep a close eye on the condition of the snow surface while you're traveling. When it gets wet or when you see wet snow rolling downhill, it is time to move to gentle terrain or slopes where the snow surface is colder and drier. Wet loose instabilities can develop rapidly; think minutes rather than hours. Minimize the time you spend below all large, steep slopes in the heat of the day especially those that directly face the sun. 

    ADDITIONAL DISCUSSION: Weak layers of snow buried 2-3 feet deep have proven to be less reactive in this zone than in neighboring areas. That said, weird avalanches tend to happen during the first major, extended warmup of the season. Dealing with persistent weak layers is tricky. Snowpack test results become more difficult to interpret and obvious signs of instability are absent. The first clear sign of an unstable snowpack may occur when you trigger a large avalanche. These types of slides can be triggered remotely—from a distance above, below, or to the side of a steeper slope—or by smaller loose snow avalanches or cornice fall coming from above.

Avalanche Discussion

You know the saying "if you don't like the spring weather just wait ten minutes?" Well, I tried that yesterday and it was still hot... and today and tomorrow are on tap to be even hotter still. The upper 1-3 feet of snow that fell during a relatively cool and stormy month of March is undergoing rapid change. Today you'll be able to find anything from dry, cold powder to straight-up wet glop–likely all in one run.

The Dry StuffAlthough dry snow surfaces are harder to find, they're still out there. If you find drier snow, you've also landed squarely in the terrain that's been harboring our persistent slab problem. There have been 4 large, human-triggered slab avalanches since April 1st. The majority of the recorded human-triggered and natural slab avalanche activity this month has occurred on NW-N-NE-E facing slopes at middle and upper elevation. Recently, however, we've observed a handful of slides that failed on sunnier aspects including this monster on Boulder Peak. This avalanche problem appears to be most pronounced in the Boulder and Smoky mountains. 

The Middle GroundIntense warming can have unpredictable effects on rapidly settling and deforming slab + weak layer combos. Yesterday, Ben snapped these two photos (here, and here) of fresh-looking avalanches that likely failed in the last few days. More of these slides are possible today and tomorrow. Cornices (while not entirely wet) will sag in the intense heat. It's important to give these huge hunks of snow some respect as a hazard in their own right, but also know that they have the potential to trigger larger slabs avalanches as they tumble downslope. 

The Wet StuffAn uncountable number of wet loose avalanches occurred in the past few days. So far, the vast majority of these slides appear to be relatively small. I think the majority (but not all) of the shallower, wet loose avalanche activity has run its course. However, a weak freeze last night and unseasonably warm temperatures today will send meltwater deeper into the snowpack. This scenario has the potential to cause full-depth loose snow avalanches or larger, destructive wet slab avalanches. Wet slab avalanches are notoriously hard to predict, but are most likely in steep terrain where the snowpack is thin and weak. 

The snow conditions today will be dynamic and your travel plans should be too. Not all of these problems will give you fair warning before they occur and I'm choosing to travel conservatively by building in a wide safety margin to help deal with my uncertainty. 

Régions couvertes