Boletín de aludes

Stevens Pass

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Sunday will be a dangerous day in the mountains. Snow along with warming temperatures, falling on weak snow surfaces will make it easy to trigger avalanches. Some avalanches may step down to deeper layers, becoming large and dangerous. Avoid steep terrain and choose lower-angle, wind-sheltered slopes to enjoy the new snow. 

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    We expect widespread storm slab avalanches from the combination of snowfall with warming temperatures and existing weak snow surfaces. Avoid steep slopes and likely trigger points, such as convex rolls. Northerly aspects and steep wind-loaded terrain are the most likely places for large avalanches. However, with variable surfaces of slick crusts and surface hoar, steep terrain in all aspects is suspect and smaller storm slabs could step down to deeper weak layers. Shooting cracks, collapsing, or fresh avalanches are all red flags that the snow is unstable.

    Choosing simple, low-angle slopes for recreation will be key for a safe day out on Sunday. The variability in deeper weak layers and surfaces makes the sensitivity of triggering avalanches tricky to forecast. So, while you can make observations using test slopes and hand pits to observe how the new snow reacts, don't try to extrapolate your results to nearby slopes. It's better to wait until this storm tapers out and we gain more information about how our weak snowpack handles this new load. 

    Rising temperatures could push temperatures above freezing further west in the zone, making small, wet loose avalanches possible at lower elevations. 

    (12/20/2022) 

    Cracking in fresh snow, like in this photo, is bullseye data of instability. 

     Photo: Ryan Minton

Avalanche Discussion

Westerly winds and snow picked up on Saturday afternoon, bringing just a few inches of snow to Stevens Pass. The main event will be Saturday night and Sunday, and we will likely see between 1 and 2 feet of snow. Easterly flow might help keep the pass-level temperatures below freezing, but lower elevations in the western portion of the zone could see a transition to rain below 3000ft.

On Friday, NWAC forecasters near Lichtenberg found widespread, variable wind-affected surfaces. This wind effect was significant even in typically wind-sheltered terrain. In the area they traveled, these wind slabs were stubborn. However, in a snow profile, the wind-stiffened snow rested over faceted snow and surface hoar and slid easily in shovel tilt tests. They found the January Drought Layer (JDL) buried approximately 2 feet deep. While the JDL was notably weaker than the overlaying snow, stability tests were unremarkable. They also noted natural, small, dry loose sluffs in steep terrain. On Thursday, observers in the Lanham Creek area reported widespread blowing snow and sensitive, shallow wind slabs near the ridgeline. 

We are uncertain about the tipping point for precipitation totals could be for the JDL. But, these persistent slab avalanches could become active with this storm. The variable distribution and previous observations suggest that if these slides become more active, they'll likely be much deeper. They could be hiding in more benign terrain sheltered on northerly slopes. Stick to an "assessment mindset," step into new terrain slowly, and assess the snowpack for strong over weak layering before committing to steep terrain. Choose lower-angle slopes if you find a stiffer slab over weak, surgery snow or experience collapsing/cracking. 

The Stevens Pass Zone picked up 2-3ft in the first week of February, burying the JDL. Following the initial storm, there were numerous reports of whumpfing collapses and some shooting cracks, but no reports of associated avalanches in this zone. In zones to the south and west, there were numerous reported persistent slab avalanches on the layer. Sunny days produced small wet and dry loose avalanches and formed a melt-freeze crust on southerly slopes that is now buried by the new snow. We're monitoring the JDL, as it's still weak and close enough to the surface to be a problematic weak layer with big enough future storms. 

You can help us build the forecast by submitting an observation HERE or via the Avy App. 

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