Bollettino valanghe

Central Cascades

Central Oregon Avalanche Center
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Pericolo valanghe

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

In sintesi

Triggering avalanches will be likely at all elevatioins and on all aspects. Be aware that you can trigger an avalanche in wind deposited snow and the new storm snow on slopes that are 30 degrees or steeper, especially in steep, convex, and unsupported terrain. Be cautious with your terrain choice and recognize signs of unstable snow such as cracking and previous avalanches as these are good indicators that avalanches can occur.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    We have had nearly 20 inches of new snow out of this storm combined with sustained westerly winds. The wind has been moving a lot of snow.  Wind slabs have the potential to be larger than what we normally see. Also they are most reactive to triggering during the storm and up to a day after the storm. Saturday is not the day to tangle with steep wind loaded terrain. 

    Wind slabs may show up in places like clearings and areas with sparse trees even below treeline. Remember burned areas and slopes with dead trees can experience a big wind affect and get a lot of wind deposited snow. 

    Wind slabs will not be everywhere, so use visual clues to identify where wind slabs have formed and are building below ridge tops, peaks, and around features that catch blowing snow from cross slope winds. Monitor the depth of wind deposited snow. As the new snow stacks up and wind slabs become deeper, resulting avalanches can become larger. 

    Utilize small features or low angle terrain to evaluate the wind slab problem. Look for cracking in the surface snow. Anytime you observe cracking in wind drifted snow, or if you see signs of previous avalanches, these are good indicators that you can trigger an avalanche. 

    This problem can be avoided by sticking to the sheltered slopes where little wind effect has occured. 

    (3/23/2023)

    Example of the typical appearance of wind drifted snow.

    Photo: Aaron Hartz

  • Storm Slabs

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

    On Friday the storm snow had more cohesion than I was expecting given the relatively cold temperatures. I found cracking on steep rollovers especially where the snow had been slightly touched by the wind to add a little cohesion to the surface snow. As more snow comes in and the snow piles up, storm slabs will be something to be cautious of on Saturday. Use small safe test slopes to evaulate the storm slab problem and look for cracking or slabs breaking and sliding. Storm slabs have a higher liklihood of initiating on steep convex slopes. Look for more planar and lower angle terrain to increase your safety margin. 

    Triggering a storm slab will be likely anywhere the wind has not stripped the new snow away.

    (3/24/2023)

    On Friday I was finding widespread cracking in the storm snow on convex rolls below treeline on north facing slopes. I triggered several very small storm slabs, but they were on small features. 

    Photo: Aaron Hartz

  • Loose Dry

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

    On Friday I triggered small dry loose avalanches in steep terrain. In some cases they were directly adjacent to where I was getting cracking in the storm slabs.  Dry loose avalanches in steep terrain will have the chance to entrain more snow and run farther that usual.  Be especially cautious in steep and committing terrain, above terrain traps, cliffs, trees, and constricted terrain such as gully features. 

    Triggering a dry loose avalanche will be likely anywhere the wind has not stripped the new snow away. 

Avalanche Discussion

Cornices are a problem, but I can only add 3 to the above list. Cornices  breaks will be possible near and above treeline and primarily on north, east, and southeast facing slopes. However, outliers could be out there on other aspects. Fresh cornices can be fragile,  break easily, and can trigger slides on the slope below. Be cautious when approaching ridge tops where cornices may be lurking over lee slopes. Stepping out onto a cornice could result in a break and a fall onto the slope below. 

On Friday, I was finding the dry loose and storm slab problem on the same slopes. That is a bit unusual. With similar conditions on Saturday I expect the same. 

Avalanches happen mostly in terrain 30 degrees or steeper. We have a lot of problems to deal with tomorrow, but you can still find terrain that is safe. Some avalanches could be small and some could be large. Each avalanche type is different and it is important to recognize where they can be found and triggered. 

Have fun out there, it is a powder day after all :)

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