Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Open full map
Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You could trigger 1-2 foot thick avalanches in wind-affected and sheltered terrain. Avalanches are most likely on shady aspects (facing NW-N-NE) and where the wind has formed large drifts or slabs.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2

    In the past week, skiers and riders triggered several 1-2 foot thick avalanches. Many of the slides appeared to fail on a thin layer of surface hoar. The most recent slide was triggered Tuesday, as a rider north of Fairfield crossed a slope for the second time (report). 

    Recent avalanche activity is focused on NW-N-NE aspects between 8000-10,000' in elevation (view graphic). The avalanches released in sheltered and wind-affected terrain. The surface hoar layer responsible for many of these slides is thin, and some of the crystals are relatively small, making them difficult to identify in snowpits (photo). Slopes that lack surface hoar may harbor a weak layer of facets and/or crusts. 

    Persistent slab problems can be hard to deal with. Avalanches may break wider than expected or higher on the slope above you. Tracks on a slope don't mean it's safe. You may be able to trigger a slide after several riders have safely climbed or descended a given slope. Given the numerous observations of this layer across the forecast area, you should assume this problem exists until proven otherwise. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability.  

    Very steep slopes over about 35* are most likely to produce avalanches. You can significantly reduce your odds of triggering a slide by steering clear of large wind drifts and by avoiding steep middle and upper elevation slopes on the northern half of the compass.

    ADDITIONAL DISCUSSION: In addition to the persistent weak layers in the top few feet of the snowpack, there are more deeply buried layers to keep on your radar. These facets (often above, below, or in between crusts) are buried beneath dense, 2-4+ thick slabs—making them difficult to trigger but capable of producing very dangerous avalanches. While triggering them is unlikely, it can't be ruled out in steep, rocky, wind-affected terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. 

    (1/15/2023) This avalanche was triggered by motorized users in Pole Creek, probably on January 14th. It likely failed on a persistent weak layer buried in the first week of January. 9200', N.

Avalanche Discussion

I added another slide to the avalanche database this morning (view the list here). It fits the overall pattern of generally sheltered, shadier terrain that's produced several avalanches since Saturday. Facets and/or crusts may be to blame in a few recent slides but surface hoar is the most likely culprit. Here's a little refresher on surface hoar along with a few things to consider when dealing with this sneaky weak layer:

  • Surface hoar formation is most effective on clear, calm nights. Locally, we often see surface hoar growth as humid air lingers following the passage of a storm. 
  • While surface hoar can spring up overnight, it is also easily destroyed. Wind, rain, sun, and sluffs can all disrupt this layer before burial. This leads to "spotty" distribution. You could find it on one slope but not the next.
  • In order to better avoid this problem, it's helpful to imagine where it's most likely to survive until burial. Commonly it's found in small clearings and open, wind-protected terrain on shadier aspects (example). It lurks well below windy ridgetops, often waiting to be triggered on steep rolls further downslope than the "obvious" starting zone. 

It's important to realize that we're all in a bit of unfamiliar territory. Widespread, surface hoar is not common in this area. If you've spent most of your backcountry days here, you probably don't have much experience dealing with this type of instability. Its "pockety" distribution can catch us off-guard. Slides failing on surface hoar can break above you and wider than expected. While recent slides have not been "huge", around half were large enough to bury or injure people, and all could carry someone into a gully, through trees, or over cliffs. Picture where even a small avalanche could carry you before committing to playing in large or consequential avalanche paths.

Regioni coperte