Bollettino valanghe

Stevens Pass

Northwest 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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In sintesi

The first big warming event of the year, combined with recent snow and a weak snowpack, means you need to carefully assess the snowpack and make conservative terrain choices. To reduce the risk of triggering wet avalanches, time your travel to be off of slopes before they become wet and weak. Use extra caution and beware of snow coming down from overhead slopes.

Problemi valanghivi

  • Loose Wet

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

    Full sunshine and 11,000 ft freezing levels will make quick work of surface crusts, destabilizing cold underlying snow.  Cool easterly winds may not be enough to keep the wet avalanche activity in check. Conditions may change quickly once snow surfaces break down, revealing moistening snow (that's good for snowballs) underneath. This moist snow provides fertile ground for entrainment as snow sheds off cliffs and trees. Keep in mind that even if you are on cold, dry snow in the shade, slopes above you may be impacted by sunshine, and overhanging cornices can fail without warning.

    Avoid travel on or directly under steep slopes where you see signs of instability, like rollerballs, pinwheels, or loose avalanches of any size. Wet, sticky snow is a key observation that slopes around you are becoming unstable. Wet loose avalanches can sometimes pull out a slab as they descend.

    Wet loose avalanches may be much larger on Friday than in the example pictured from the Olympics.

    Photo: Kaitlin Harrigan

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    Although the deep layer is getting more buried and gaining strength in recent days, meltwater in the snowpack, wet avalanches, and cornice falls could all trigger this unlikely type of avalanche.

    Avalanches that run on deeply buried weak layers could be 3-4ft or deeper and can propagate widely across the slope. You won't get signs of instability before triggering one, as the layer is too deep. Your best bet is to remain aware of the terrain around you, staying out of complex alpine terrain and off of steep, unsupported slopes or those with wet loose or cornice fall hazard.  Any recent or active wind transport onto a slope will also increase your likelihood of triggering one. You can find a thin layer of softer facets that is slowly gaining strength over a hard crust, about 3.5-4.5 ft below the surface at upper elevations (above 6,000ft) and further east in the zone.

    (3/5/2024)

    A large rider triggered deep slab on a W aspect of Jim Hill at 6,500ft. 

    Photo: Nate Hough-Snee

Avalanche Discussion

Loose wet avalanches has been gradually ramping up over the last several days. Wet loose activity was reported on a variety of aspects near Stevens Pass on Thursday and Friday, with some up to size D2.

Following a cooler storm cycle, we've entered a dry and unseasonably warm period. This abrupt change brings a lot of uncertainty. The best way to deal with uncertainty is to limit your terrain selection to simple, lower-angle slopes with reduced overhead hazards. Big natural avalanches shouldn't be taken lightly. 

From March 9-13th, Stevens Pass picked up 1.71” of precipitation. Strong winds redistributed snow onto leeward aspects with signs of transport observed in wind-affected areas. E and NE winds will be light, but may still transport snow near ridgelines on Friday. Steer around steep areas of active wind deposition.

There were three notable slab avalanches reported in recent snow this week. On Wednesday, two separate skier-triggered avalanches were reported. One was reported to have failed at a surface hoar layer over a crust that was likely buried on the 9th. Both were about 12” deep, and one was triggered remotely. A large natural wind slab avalanche was reported on a leeward, east aspect around 5000’ just outside of the Steven Pass Mountain Resort boundary. It probably occurred overnight on the 11th.

We're in an extended stretch of unseasonably warm, sunny weather. It will be the first big, spring-like warming event of the year, with high temperatures in the 50’s and freezing levels over 11,000’. Very warm conditions through the weekend could produce significant slab and loose snow avalanches.

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

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