Avalanche forecast

Central Cascades

Central Oregon Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Triggering avalanches will be likely at all elevations. The potential for large avalanches will increase throughout the day.  Increase your safety margin by sticking to slopes less than 30 degrees steep, especially if you observe signs of unstable snow such as cracking, previous avalanches, or if you have uncertainty in the stability of the snowpack,

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    As the snow falls and the wind blows, wind slabs will build on lee terrain features. Wind slabs are most sensitive to triggering when they are fresh. This will be a day to carefully evaulate wind loaded slopes. Avalanches have the potential to be large. 

    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, avalanches can become larger. Look for signs of blowing snow to indicate where wind slabs are building.

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

    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. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    This problem will be more likeley at the lower elevations where higher temperatures will bring on a more cohesive layer of new storm snow. Examine the new storm snow for cohesion....hand sheer tests are useful for this.

    As new snow comes in and the snow piles up to 8" or more, use small safe test slopes to  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/or lower angle terrain to increase your safety margin. 

    Storm slab avalanches will be likely anywhere the new snow has not been stripped away by the wind and is forming a cohesive layer.

     

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

     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 such as cliffs, trees, and constricted terrain like gully features. 

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

Avalanche Discussion

There have been reports of patchy buried surface hoar on northerly aspects near and below treeline. An avalanche was skier triggered on a layer of buried surface hoar on Tuesday with with a 70 cm (28") crown on a north facing slope near treeline. With an abundance of new snow coming in, this will add weight to the upper pack and any slopes that are harboring buried surface hoar have the potential to avalanche. Be cautious if you are planning on dropping into steep and committing slopes on northerly aspects. Find a safe location to dig and check out the snowpack. Buried surface hoar often presents as a thin line in a pit profile and can often be picked out with compression tests. By Saturday afternoon any buried surface hoar could be up to a meter (3') deep. The patchy nature of this problem will be tricky. Snowpack testing gives limited data and the terrain can be vast. Persistent slab avalanches have the propensity to propagate farther than our typical storm problems. 

 With new snow and wind transport, cornices will be growing above lee slopes. 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 hanging over lee slopes. Stepping out onto a cornice could result in a break and a fall onto the slope below. 

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