Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Very dangerous avalanche conditions exist, from the valley bottoms to the mountain tops. Avalanches capable of destroying your house are very likely. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Avoid avalanche terrain.

The backcountry Avalanche Warning does not apply to the HWY 21 avalanche program.

Problemi valanghivi

  • Wind Slabs

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

    Yesterday's storm brought 18-24" of snow (1.5-1.8" of SWE) to this zone. Snowfall was accompanied by moderate to strong winds blowing out of the SE-S-SW. This combination built very large, dense, 1-3 foot thick wind slabs on many slopes. Triggering a wind slab avalanche large enough to bury you or worse is very likely today.

    You're most likely to find these slabs in middle and upper elevation terrain. Wind slabs commonly form along ridgelines and near mid-slope terrain features like ribs and gullies. This zone typically does not have wind slab problems at lower elevations, but the wind was blowing hard enough that you may find reactive slabs on road cuts and the steep banks above creeks as well. 

    Intense March sunshine will quickly melt the snow that fell yesterday, producing widespread loose snow avalanches. These will become more frequent, larger, and more destructive as the day warms. Wind slabs and cornices that fail can be very effective triggers for the enormous, destructive persistent slab avalanches described below in Problem 2. 

    (3/10/2023) This very large slab avalanche failed in a heavily wind loaded location on a NW-facing slopeat 6,800' above Croy Canyon. Large amounts of snow are being transported in this photo.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2.5–3.5

    The new snow and wind slabs described above are pushing the weak layers in our snowpack up to and past their breaking points. Avalanches that fail on these layers will be massive and unsurvivable. Picture an avalanche large enough to destroy your house and you start to get the idea. These types of slides may continue to occur naturally today.

    Avalanches that fail on these layers will break very wide, wrapping around multiple aspects and connecting multiple avalanche paths. These slides can run the length of the avalanche path, impacting flat terrain long distances away from steeper slopes. 

    The only way to manage this problem is to avoid avalanche terrain and terrain exposed to overhead hazard. This includes meadows that are well away from the base of any steep slope. You can trigger an avalanche that fails thousands of feet above you from flat terrain at the valley bottom.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain (great skiing and riding conditions) is an excellent example of a slope that did not need wind loading to become unstable. 

Avalanche Discussion

Yesterday was extraordinarily dangerous. Today is not significantly safer. 

Visibility was poor in our region for most of the day. However, a brief clearing in the afternoon allowed us to see the aftermath of a truly impressive avalanche cycle in the mountains above the Wood River Valley. Very large avalanches were observed on many aspects and at all elevations (video here). Avalanches hit multiple houses and dammed the Big Wood River in several locations (photo). We don't have direct information from our other forecast areas, but it is a safe bet that this morning's sunrise will light up the crowns of numerous very large avalanches.

Snowfall continued into the evening hours and the wind continued to build slabs and add stress to the snowpack. Today's bright sunshine and mild temperatures will warm the upper layers in the snowpack, causing the snow to deform and pull itself downhill. This additional creep can produce natural avalanches, even without additional loading from snow or wind. The heat of the sun will also result in numerous loose snow avalanches and cornice failures. These masses of snow moving downhill can be very effective triggers for much larger avalanches. 

Avalanches will not be limited to the backcountry today. Warm temperatures and sun will cause roofs that are loaded with snow to avalanche. Steep slopes threaten many urban locations in the Wood River Valley. Pay attention to what is above you. We are dealing with unusually dangerous conditions and we need to behave accordingly. Today is an excellent day to practice avoidance. Avoid slopes steep enough to slide and slopes exposed to hazard from above. 

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