Avalanche forecast

Northern Wallowas

Wallowa Avalanche Center
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Avalanche danger

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

Wet loose avalanches are possible on steep rocky south-facing slopes in the PM.  Avoid and stay out from underneath these slopes as temperatures rise. Increased southerly winds will build pockets of reactive wind slab on the north aspects at and above treeline. Avoid areas of recent wind deposition >35 degrees and potential trigger points like convex rollovers, wind pillows below cliff bands, and cross-loaded terrain features mid-slope.

This forecast is sponsored by CB Construction.

Avalanche problems

  • Loose Wet

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

    These sunny warm days are splendid. Enjoy. But lots of sun brings lots of heat to the snowpack. In the Southern Wallowas, the potential for wet loose avalanches will be more pronounced at lower elevations in the steep canyons of Eagle Creek and its tributaries.

    As we approach the spring Equinox the solar input into the snowpack can be intense, especially on any steep rocky slope slightly tilted toward south. As the snowpack warms up around rock outcroppings and cliff bands wet loose avalanches become a real possibility. If you start to see rollerballs, pinwheels, and small point releases coming off steep rocky south-facing terrain - then it is a good idea to stay off and out from underneath those slopes during the afternoon hours. If you find yourself bogging down on your sled or sinking in above your calves into wet gloppy snow, then you should also lower your slope angles below 35 degrees.

     

    (3/17/2023)

    Wet loose avalanches occuring during the afternoon on steep rocky south-facing terrain in the alpine.

    Photo: V. McNeil

  • Wind Slabs

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

    Moderate south winds overnight and throughout today will likely create pockets of reactive wind slab 1-2' thick at and above treeline.  You can identify wind slabs by looking for smooth textured pillows below ridgeline and on the leeward side of terrain features like ribs and gullies. Many of the most recent avalanches reported or witnessed with the last storm cycle pulled out on steep connected aprons below cliff bands. Avoid potential trigger points like steep wind-loaded slopes > 35 degrees, convex rollovers, and unsupported slopes above and below cliffs.

Avalanche Discussion

A New Mindset

It is easy to succumb to the enticing allure of fresh powder on sunny days. The sunshine warms our souls, bouys our spirits, and increases our risk tolerance. As we move toward the spring Equinox - March 20th this year - we need to change our mindset from a wintertime perspective to a springtime perspective. A winter snowpack is very different from a spring snowpack. For one, we begin to see alot more potential for wet loose and wet slab avalanche problem types. As the sun climbs in the sky more slopes start to take solar radiation. Some of these slopes haven't seen sunshine since November. As the famed snow scientist, Ed LaChapelle noted, "Snow does not respond well to rapid change." This means mechanical (increase in stress like more snow load) or thermal (decrease in strength due to melt). At the height of winter most of our instability arises from mechanical means - a lot of snow in a short amount of time. In the springtime, our instability can now include thermal factors.

The shift in mindset comes from paying attention to temperatures. If you observe from weather stations and the forecast that the temperature has or will remain above freezing for a couple nights in a row, then you can anticipate unstable conditions. If the snowpack isn't freezing, then it is melting. Melting reduces the attachment of the grains amongst themselves and can pool up on more impermeable layers in the snowpack, like on top of crusts, and reduce the attachment of layers above. Ideally, you want to see temperatures at night dipping down into the low to mid-20's. A slight freeze of 30 degrees isn't going to set up the snowpack much below the top couple inches. As daytime temps increase that top couple inches will soften and then you'll find yourself in a soupy mess.

In addition to keeping an eye on nighttime temps, also pay attention to what is going on with sunny slopes during the day. If you start to see rollerballs, pinwheels, and small point releases coming off steep rocky south-facing terrain - then it is a good idea to stay off and out from underneath those slopes during the afternoon hours. If you find yourself bogging down on your sled or sinking in above your calves into wet gloppy snow, then you should also lower your slope angles below 35 degrees. 

Other Problems

A new mindset shouldn't have us disregarding the wintertime problem types. We can get dig dumps in the spring, which will add a lot of stress to the snowpack in a short amount of time. If you see snow totals heading over 12" in 24 hours, then you can anticipate unstable storm slab conditions. In the spring we can get more rain on snow events. If you see temps above freezing and SWE - snow water equivalent - on the Snotel sites climbing above 1" in 24 hours, then you can anticipate unstable conditions. Wind slabs will be a potential problem any time of year. As forecater Kelly McNeil pointed out yesterday, "As you climb into the upper elevations remember that wind slabs could still be hanging out and that cornices may be starting to warm and sag.  Watch out for these massive overhanging snow waves as they can break back further than you expect.  Cornices are very dangerous and unpredictable."

 

 

 

 

 

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