Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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In sintesi

In the past few days, we've observed several large, destructive slab avalanches. These avalanches may fail naturally or can be triggered remotely—from a distance above, below, or to the side of steep slopes. Similar slides are likely again today. Traveling safely in avalanche terrain is difficult. Don't linger below large avalanche paths and avoid areas with wet, soggy snow.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Yesterday, we observed wet slab avalanches in the Pioneer Mountains (see photos above/right). Expect this avalanche activity to continue as another weak overnight freeze and continued sunny, warm weather combine to send meltwater deep into the snowpack. The snowpack in this zone is very weak and faceted, particularly on slopes that face the northern half of the compass. Avalanches may occur when meltwater weakens these facets either in a weak layer within the snowpack or near the ground.

    Wet slab avalanches are almost impossible to accurately forecast on a slope scale and the resulting slides often wipe out much of the season's snowpack. The best way to manage this problem is to avoid steep slopes with soggy snow. If the snow surface begins to resemble mashed potatoes or if you're punching through crusts that were supporting you early in the day, move to slopes with cooler, drier snow or call it a day. 

    ADDITIONAL DISCUSSION:Wet loose avalanches are possible again today. Large, gouging wet loose avalanches may occur as meltwater moves deeper into the snowpack. Smaller, loose snow avalanches have the potential to pull out wider, more destructive wet slab avalanches lower on a slope. Wet loose instabilities can develop rapidly; think minutes rather than hours. Any firm surface you find this morning is likely to be fleeting.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    On Tuesday, we observed a 1500' wide, destructive slab avalanche on Boulder Peak (sunny slope), a wide slab avalanche on Bear Peak (shady slope), and a sizable slab in the Newman Ck drainage (partial sun/shade). Observers reported natural slab avalanche activity near Horton Peak (sunny slopes) and in the Owl Creek drainage (shady slopes). This is in addition to the  4 large avalanches skiers and riders triggered since last week's storm, many of them remotely (from a distance above, below, or to the side of a steeper slope).

    Tuesday's activity involved sunnier SW-S-SE aspects as well as the problem faceted layers on E-NE-N-NW aspects we've been talking about for days. You're more likely to trigger persistent slab avalanches in areas where the wind has stiffened the snow surface or formed drifts, but they are possible in sheltered terrain as well. As we are in the midst of the first major warm-up of the season, the wise move is to stand back and watch the show instead of trying to outsmart exactly where the persistent layers are most likely to fail. 

    Dealing with persistent weak layers is tricky. Snowpack test results become less reliable, and obvious signs of instability may be 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've been trying that and it's still hot... The upper 1-3 feet of snow that fell during a relatively cool and stormy month of March is undergoing rapid change. Today you may be able to find anything from dry, cold powder to straight-up wet glop–likely all in one run.

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, another 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. Yesterday, Ben took these photos of wet slab avalanches in the Pioneer Mountains (Hyndman, Handwerk). This problem should remain on your radar until the snowpack locks back up with a solid, deep freeze.

The Middle GroundIntense warming can have unpredictable effects on rapidly settling and deforming slab + weak layer combos. Wednesday, 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 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 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. 

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