Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Recent strong winds transported snowfall from the past week, forming fresh, stiff wind drifts and stressing buried weak layers. The size and chance of triggering avalanches are higher in the western portion of this zone (Dollarhide Summit to the Soldier Mountains) than in the mountains near Ketchum and Carey. Triggering an avalanche 1-3 feet deep remains possible, especially on steep, upper elevation slopes. You can dramatically reduce your risk of getting caught in an avalanche by sticking to terrain that is sheltered from the wind.

Problemi valanghivi

  • Persistent Slabs

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

    Layers of weak snow can be found near the ground and in the middle and upper portions of the snowpack:

    1. Depth hoar exists near the ground on all aspects (excepting low elevation slopes that are snow-free). This is the snow that we've been talking about all season long and seem destined to talk about for the remainder of the season.
    2. In the middle of the snowpack, several interfaces have produced both avalanches and unstable test results in recent days. These layers appear to be problematic where accompanied by a crust.

    Ben found ugly snowpack structure and poor snowpack test scores near Dollarhide Summit (observation, photos) and in Adams Gulch in recent days.  He also found a large, natural avalanche that appeared to have failed on a crust before stepping down to weak snow near the ground. This slide was located in exactly the type of terrain that still has me spooked in this zone: wind-affected slopes steeper than about 35 degrees. You can greatly reduce your risk of triggering a large persistent slab avalanche by playing on slopes less than 35 degrees that are sheltered from the wind.

    (2/12/2021) This avalanche was triggered by a rider NE of Wells Summit in the Soldier & Wood River Valley zone. The slide broke around 40' wide and carried the rider about 100 yards. A section of the cornice also released in the slide.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    This weekend, Soldier Mountain Cat Ski guides remotely-triggered a wind slab avalanche that broke 1.5' deep (photo above/right). Since then, strong to extreme winds have moved literally tons of snow at middle and upper elevations. Expect to find a variety of stiff and hard wind slabs in exposed terrain. Because the winds have been so strong, I expect the wind slabs to be fairly isolated and not that easy to trigger. Unfortunately, the fresher wind slabs will be very hard. While hard slabs support your and your sled's weight, they fail unpredictably when stressed to the breaking point. Hard slabs can break well above you, pulling into flatter terrain near the ridgetops. 

    Be on the lookout for stiff snow that feels "punchy" or hollow underneath. You could find the recently formed wind slabs near ridges, on the sides of cross-loaded gullies, and lower on slopes near prominent terrain features. Recognize that the wind event also added stress to the weak layers buried deeper in the snowpack (described in Problem 1 above). Any wind slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche. 

    (2/20/2021) Ski guides remotely-triggered this wind slab avalanche yesterday on Peak 2 in the Soldiers while doing mitigation work. It broke 1.5' deep. Photo courtesy Soldier Mountain Cat Ski.

Avalanche Discussion

PUCKER FACTOR: AN AVALANCHE FORECASTER'S "TIEBREAKER"

Assigning avalanche danger ratings is not an exact science. LOW and HIGH danger days are usually obvious, but choosing between MODERATE and CONSIDERABLE can be difficult for forecasters, especially when facing certain avalanche problems. The expected avalanche size and likelihood play a large role in determining the avalanche danger, but we do not have an algorithm that spits out the correct danger rating after plugging numbers into it. If only it were that simple! When we're "on the fence" between danger ratings, we weigh the danger ratings' travel advice heavily to choose a  level; how will we be traveling through terrain today? Will we consider entering starting zones? Or crossing avalanche tracks? Or riding sleds or skinning up in runout zones? 

I have my own personal "pucker factor" chart that basically describes how scared or comfortable I would be traveling in avalanche starting zones/tracks/runout zones when facing various avalanche problems. In our two central zones (Galena Summit & Eastern Mtns and Sawtooth & Western Smoky Mtns), the nature of the persistent slab problem still has me puckered. Recent natural avalanche activity - check. Recent wind loading - check. Poor snowpack structure - check. A high degree of complexity and uncertainty - check. For today, that's enough checked boxes to continue to keep me, the other SAC forecasters, and most local avalanche professionals out of all sizeable or consequential avalanche paths over 35 degrees and all wind-loaded slopes over 35 degrees. That's my tiebreaker between CONSIDERABLE and MODERATE. 

Are you likely to trigger large avalanches on all slopes today? No. Many slopes have stabilized to the point that triggering them is unlikely. The problem: with the dramatic effects of the recent wind event, I'd need a pack full of explosives to determine which slopes are relatively stable and which are teetering on the edge. Facing that degree of uncertainty, I'm too puckered to risk my life in steep, exposed terrain for now.  

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