Bollettino valanghe

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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You're most likely to trigger avalanches big enough to bury people on slopes where the wind has formed drifts or stiffened the snow surface. Triggering avalanches is also possible in very steep terrain that is sheltered from the wind. To reduce your risk, you can stick to gentler slopes with soft, fluffy snow on the surface.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    The chance of triggering large avalanches is greatest on recently wind-loaded slopes over about 35 degrees. We have two persistent slab problems to consider:

    1. "Fresh" Slabs: You could trigger 1-2 foot thick slides on middle and upper elevation slopes. The new snow that fell over the past several days has formed a soft slab above small facets or crust + facet combinations. These slabs are thicker and more dense in terrain exposed to the wind. In more sheltered terrain, triggering slides is less likely but still possible on slopes approaching 40 degrees. Watch for obvious signs of instability like snowpack cracking or collapsing. 
    2. Thicker, Older Slabs: While unlikely, the possibility of triggering a massive 2-5 foot thick avalanche remains on the table. These hard slabs also rest on weak facets and crust + facet combinations. This problem has been "quiet" this week, meaning we haven't observed recent avalanches or snowpack collapsing. That said, the poor structure (slab over weak snow) and track record (hundreds of natural avalanches around St Patrick's Day) are hard to ignore. Smaller avalanches running downslope could step down to this weak layer, triggering an unsurvivable avalanche. You probably won't see any obvious signs of instability associated with the thicker slabs, and there's an outside chance you could trigger these beasts remotely—from gentler terrain above, below, and to the sides of steep slopes.

    The combination of widespread weak layers, a developing persistent slab problem in the upper 2 feet of the snowpack, and the uncertainty associated with deeper weak layers adds up to variable, spooky conditions in avalanche starting zones. Triggering avalanches is much less likely on slopes sheltered from the wind that are closer to 30 degrees in steepness. 

    ADDITIONAL DISCUSSION: Wind and snowfall in recent days formed 1-2 foot thick wind slabs on isolated upper elevation slopes. Any wind slabs that you encounter may be perched above weak facets and/or crusts, making avalanches easier to trigger and wider than you'd expect. Relatively small wind slabs moving downhill could trigger the larger, more dangerous Persistent Slab avalanches discussed above. Look for wind slabs near ridgelines and on the sides of mid-slope terrain features like gullies and ribs. Surface textures like dunes, ripples, or pillows are clues that the wind has been at work. Cracks shooting out from your skis or machine are clear indicators that you've found an unstable slab. 

Avalanche Discussion

You probably noted the word "wind" in every section of the forecast. In sheltered terrain, the snowpack seems to be adjusting to the recent snowfall fairly well; here, triggering avalanches is possible on slopes that are 35-45* in pitch but unlikely on slopes closer to 30*. Recently wind-loaded slopes are an entirely different story, especially at the middle/upper elevation transition where the weak layers are typically at their worst. Slopes around 8500-9500' where the wind has stiffened the snow surface—even if there are no fresh drifts—should be approached with caution. Avoiding all obviously wind-loaded slopes over 30* is the prudent move today. 

Cornices are unusually large this year. Give these unpredictable beasts plenty of space by traveling far from the edge, staying where you can easily feel dirt or rocks below your skis or sled.   

Adding to the complexity is the potential for a wet, mushy snowpack at lower elevations this afternoon. Although the snow surface refroze overnight, afternoon heating could break down surface crusts and create issues in very steep, rocky terrain where the snowpack is thin. In these areas, wet loose avalanches could gouge near the ground. 

Many of us are used to a more uniform, stable snowpack this time of year, one that's seen multiple waves of meltwater followed by a freeze. The abnormally cool and snowy spring has delayed this transition, and our snowpack is in mid-winter form. Use the same caution today as you normally would in January. 

A powerful storm will cause the avalanche danger to spike Saturday and Sunday. Be prepared for whiteout conditions and widespread natural avalanche activity.  

Regioni coperte