Avalanche forecast

Central Cascades

Central Oregon Avalanche Center
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Avalanche danger

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

Triggering large wet avalanches in steep terrain on all aspects will be likely at at lower and mid elevations and possible at all elevations as the day goes on and more rain water accumulates in the snowpack. They will also have the potential to go naturally by the afternoon. If you choose to go out in the rain, manage the hazard by choosing slopes less than 30 degrees steep and stay out of the way of steep overhead terrain. 

Avalanche problems

  • Wet Slabs

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

    The wet slab problem will be more likely below treeline and near treeline. Around a half inch or more of rain is expected by the afternoon along with rising temperatures. However, this problem could creep into the alpine terrain as the snow level is expected to rise to 9k+ ft by the afternoon. The rain will add weight to the upper pack and can weaken layers and layer boundaries as the rain soaks into the snowpack. The biggest layer of concern will be the Dec. 8th buried surface hoar that exists throughout the terrain and primarily on northerly and easterly aspects and is down 40 - 60 cm (16 - 24") below the surface. This layer itself has been very quiet recently but the rain and warming could be the thing to make it fail. There are also old midstorm instabilities and some patchy surface hoar layers in the upper pack that could be sources of failure with percolating water and warming. 

    The extent of the wet avalanche problem depends one the extent rain and warming. A good strategy to gauge this problem is to dig into the snowpack and look for where the water is affecting the snow layering. As water pools at layers and layer boundaries you can judge where the snowpack will become more weak. Remember rain can add a lot of weight to the upper pack and lead to a higher chance of slabs running naturally. 

    Riding in the rain can be fun sometimes.....if you feel the need to go out in the rain be cautious and do some evaluation. As rain begins to soak deep into the snowpack, the safe bet is to ride low angle slopes. 

    Loose wet avalanches will share the same distribution as the wet slab problem but will mostly be smaller in size. 

     

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    On Friday, weather stations at 7500 + ft  were hovering near or just below freezing. The COAC Moon Mt. station (7450 ft.) recorded a high temperature of 31 degrees F.  New snow and blowing snow likely occured throughout the region at the higher elevations on Friday even as the low lying areas were getting rain. Wind slab avalanches will be more of a concern above treeline. If you venture up through the murk of rain and into the high country in the morning be cautious of wind loaded slopes. Monitor where wind loading has occured by using visual clues and observing blowing snow. Triggering a wind slab avalanche will mostly result in a small slide, but acknolwedge what is below you and be cautious of terrain traps. 

    As rain hits the mid and upper elevations, the wet slab problem could be more of a player.

Avalanche Discussion

On Friday at 6400 ft, water was observed to affect the snow only down 7 cm (about 3") below the surface before the rain turned to snow between noon and 1pm. The rain soaked snow could have been deeper at the lowest elevations in the forecast zone. The depth of rain inluenced snow will be more significant on Saturday as more prolonged warming and rain comes into play. 

In Central Oregon, some of our biggest avalanches have been wet slabs resulting from rain on snow, especially when we have intact winterlike layers in the snowpack. 

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