Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Stick to simple terrain with limited overhead hazard as soaring freezing levels usher rapid change to a cold snowpack. As shallow crusts break down with daytime heating, the potential increases for large natural and human-triggered avalanches. Cornice fall and snow shedding off rocks or cliffs all serve as potential triggers from above.

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, an awakening upper snowpack with increased wet loose and cornice fall activity could disturb the deeper layer.

    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. This layering (and the likelihood of triggering avalanches) is most pronounced at upper elevations (above 5,800ft) and further east in the zone. In the coming days, water may penetrate to the weak layer, creating wet slabs. While we don't expect this tomorrow, the first evidence might be in shallower snowpack areas and southerly aspects.

    (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

We've entered a dry and unseasonably warm period following a cooler storm cycle. That 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 hazard. Big natural avalanches aren’t really the kinds of things that should be taken lightly. Take heed of harbinger avalanches, whether human-triggered or natural. The danger may change quickly and if you're not in tune with the changes around you, it's not a bad time to simply stick to non-avalanche terrain.

Since March 9th, Stevens Pass has picked up 1.71” of precipitation. Strong winds have 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.

Loose wet activity has been gradually ramping up over the last several days. Small wet loose activity was reported on a variety of aspects around Stevens Pass Ski area on Thursday.

There were three notable slab avalanche observations so far this week. On Wednesday, two separate skier-triggered avalanches were reported. One was observed to have failed at a surface hoar layer over a crust. Both were about 12” deep, and one was triggered remotely. We don't yet know whether the warming will hasten the healing of the surface hoar or just stiffen the slab above it. Also, a large natural avalanche was reported on a heavily wind-loaded, east aspect around 5000’ just outside of the Steven Pass Mountain Resort boundary. It probably occurred overnight on Monday.

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. 

Regioni coperte