Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Today will be bright, sunny, and deceptively dangerous. You can trigger large, destructive avalanches, and you can trigger these slides from long distances away. The first sign of instability may be the unsurvivable avalanche you trigger. Smaller loose snow avalanches will release naturally throughout the day as the sun warms the snow. These can become large in big terrain and can also trigger much larger slides on deeper weak layers as they travel downslope. 

Problemi valanghivi

  • Persistent Slabs

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

    Triggering a wide, 2-4 foot thick avalanche large enough to bury people and possibly destroy a house remains possible. Dense slabs exist on nearly all slopes, and you'll find facets and/or surface hoar on shadier aspects and crust + facet combinations on sunnier slopes.  

    The odds you will trigger a Persistent Slab are decreasing, but the consequences remain severe. Don't expect to see obvious signs of instability, like snowpack cracking or collapsing, before triggering a slide. You may be able to trigger avalanches from flat or low-angle terrain long distances away from steep slopes.

    Sadly, the only surefire way to manage this problem continues to be avoiding avalanche terrain, including the base of slopes that are threatened from above. 

    (1/22/2024) The debris of this slide ran into a creek, a lower and mid-elevation terrain trap that is characteristic of the Banner Summit Zone. Terrain features like these multiply the consequences of these slides.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–1.5

    February storms brought well over a foot of snow to this zone. You will encounter a broad range of new snow issues today:

    Loose snow: Sluffs of new snow will be easy to trigger and will release naturally throughout the day as the sun warms the snow. Natural loose snow avalanches will occur first on E/SE-facing slopes and work their way around to S and then SW/W slopes as the sun arcs across the sky. Initially, these slides will have a dry character, but they will become wetter, denser, and more powerful as the day warms and the surface snow melts. 

    Wind slabs: Winds have been generally light in recent days. If you head to upper elevations, you may find small, reactive slabs in places where the wind has been transporting snow and building drifts. Wind slabs that formed earlier in the storm when conditions were much breezier will be hard to identify visually, thanks to the low-density powder sitting on top. 

    Slabs at new/old interface: Snowpit observations and natural avalanches point to the potential for avalanches failing at the base of the new snow, even in terrain sheltered from the wind. Our observations are limited, and we can't yet say with confidence if this interface will be a longer-lived weak layer or just a flash-in-the-pan. Some of the observed avalanches that failed on this layer broke many hundreds of feet wide. 

    Remember that all of these smaller avalanches will take place on the stage set by the Persistent Slab problem above. Smaller slides can be effective triggers for much larger Persistent Slab avalanches as they rocket downslope. 

Avalanche Discussion

Today you will be tasked with managing a dangerous snowpack and managing your own excitement and expectations. We emerge from a 10-day series of storms into a bright, beautiful, and dangerous world. The problems you'll encounter today broadly fall into new snow and old snow boxes. The Persistent slab box above describes the older snow, and the Wet Loose box describes the snow that fell in February. Let's start at the top:

NEW: Today's sunshine will produce a widespread shedding of the new snow in the mountains. Expect to see loose snow avalanches follow the sun around the sky, starting on E/SE slopes and moving towards S and then SW/W slopes as the day progresses. These slides will initially have a dry character but they are likely to become wetter as the day heats up and they entrain moist snow. In terrain affected by the wind, you may find some small, reactive wind slabs. Conditions have been fairly calm for the past few days, but it doesn't take much of a breeze to push the low-density snow around. Wind slabs that formed earlier in the storm will be hard to recognize visually, thanks to the low-density snow on top. In terrain shel

OLD: A widespread layer of weak snow is buried in our snowpack. This layer has produced countless natural and dozens of human-triggered avalanches this season and will continue to do so. A thick, dense slab of snow is sitting on top of this weak snow, making it slightly more difficult to impact the weak layer. Unfortunately, this same dense slab is very well connected to itself, and if you start an avalanche involving this slab it has a good chance of breaking very wide. 

There is a lot going on in our snowpack, and the warm sun and deep powder will make it hard to focus your attention on the problems at hand. Head out into the mountains expecting this. It may be the most beautiful winter day you've seen this year. I'd love nothing more than for each and every one of you to come home safe and write to me about all of the powder you safely feasted on. 

Regioni coperte