Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Heads up! Daytime warming should take hold of the snow and avalanche conditions this weekend, increasing the chances for hazards like cornice falls, wet loose avalanches, and very large deep slab avalanches. The danger is lower early in the day, but should rise as the sun and warm temperatures influence the snowpack. Keep timing and overhead hazards in mind, and be ready to adjust your tour plan as temperatures heat up. 

Avalanche problems

  • Loose Wet

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

    Early in the day most surfaces should be frozen crust. Expect east aspects to begin warming up first, and then south and west later in the day. Look for rollerballs, tree bombs, and feel for heavy wet snow as indicators that things are starting to happen. Slides may become large on steep or rocky slopes as the day progresses and warming continues to break down the crusts in the upper part of the snowpack. Use timing to your advantage, and be ready to steer clear of certain steep slopes. Wet loose slides could trigger wider wet slab avalanches on some slopes, and they could be quite dangerous in their own right.

    A D2 (large) wet snow avalanche from earlier this winter.

    Photo: Irene Henninger

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    Cornices have gotten quite large and we've been receiving reports of one or two cornice falls a day over the past week. Stay out from underneath overhanging cornices in the chance they do fall.

    A few isolated, but deep (up to 6ft deep) slabs have been observed from earlier in the week. While the chances of actually triggering one of these is probably slim, large loads like snowmobiles, big cornice failures, or perhaps a warming event like this could still do it. If any very large slides did occur, they would run much further than you might expect, so best to add in lots of buffer room well away from large steep slopes while your out in the mountains. Steep, large and unsupported slopes might be worth steering clear from once daytime warming takes hold.

    (3/16/2023)

    Cornice fall over a recent skin track in Cutthroat drainage observed on Thursday morning.

    Photo: Ryan Minton

Avalanche Discussion

Three very large natural avalanches were reported on Thursday; A D3 on a NE aspect off Kangaroo into Willow Creek, a D2.5-3 above the Slot on a NW aspect of Kangaroo, and a D3 from an E aspect in Cutthroat. Many of these ran beneath large rocky cliffs where storm snow deposited more deeply. The slide in Willow Crk appears to have run down to the ground on a moraine, with a crown estimated at 3-6ft deep. Last weekend, 2-4ft deep slabs were reported from areas such as Liberty Bowl near Blue Lake Col and in the Hairpin Valley.

Significant snowfall and intermittent wind events since late February have added about 3ft to the snowpack, and now we're entering a warming trend. This weekend the snowpack will really begin to feel the effects of the warming trend, and the warm temperatures and sun should destabilize the snowpack during the daytime. 

The Valentine's crust is 3-5 feet below the surface in the western half of the zone, including near Washington Pass, the upper Silverstar drainage, and Hart's Pass. You can expect to find it closer to the surface at lower elevations and further east in the zone. There have been numerous observations and snowpack tests indicating weak snow and poor structure below this crust. If you're motivated to dig deep enough, you can probably still find the January 5th surface hoar. We have less of an understanding of the progression of these layers east of Mazama and the Twisp River drainage.  

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