Boletín de aludes

Snoqualmie Pass

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Multiple nights without a solid refreeze enable meltwater to rapidly unglue the fabric of the snowpack. The resulting ongoing shed avalanche cycle may peak on Sunday, creating destructive springtime avalanches that become increasingly unmanageable during the warmer hours of the day. Careful route planning and a safe, early exit strategy will be critical as the day heats up.

Problemas de aludes

  • Loose Wet

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

    With each passing night of above-freezing temperatures, loose wet slides are becoming larger and increasingly difficult to manage.  Several feet of wet punchy snow sits on the surface of most slopes. Avalanches could originate from steep and rocky terrain above you and travel far downslope. On Saturday, loose wet avalanche activity became widespread by the afternoon and you can expect a similar increase in activity during the day on Sunday. Plan your day to avoid traveling below large avalanche paths particularly as temperatures rise. 

    Natural or human-triggered wet slides may occur on slopes steeper than 35 degrees once the sun rapidly breaks down a shallow crust. Once you sink past your ankle, seek out lower angled or more frozen snow.

    (4/17/2021) Wet Loose avalanche entraining significant snow on a N aspect in the Kendall Adventure zone. Give steep slopes such as these a wide berth as the snowpack heats up. Photo: Ian Nicholson.

  • Glide Cracks

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    We have a deep mid-April snowpack and glide avalanches continue to fail unpredictably where that snowpack still clings to rock faces. A large natural glide avalanche occurred above the Alpental access road Thursday night. Similar large and even very large (D3) glide slabs continued to release across the Washington Cascades through Saturday. We know that water is moving in the snowpack and in many instances reaching the ground. Continued hot weather on Sunday will only exacerbate this problem. Glide avalanches can release without warning any time of the night or day. Don’t linger underneath slopes where you see crevasse-like glide cracks.

    (4/16/2021) This natural glide avalanche occurred overnight above the Alpental access rd. 4/15-16/21: NE 3400'. WS-N-D2-G: Photo: Alpental Ski Patrol

Avalanche Discussion

By Sunday, we're on our fifth day of continuous above-feezing temperatures in the Snoqualmie Region. High temperatures in the 3000-5000 ft elevation range were in the 50s on Saturday. Although it has been over a week since the last precipitation, the snowpack gains liquid water rapidly at these temperatures. Snowmelt continues to percolate deeper into and rapidly transition our snowpack. Simple red flags like widespread avalanche activity, recent large avalanches, 5 nights above freezing, and temperatures increasing into Sunday all suggest the ongoing first major shed cycle of the year will continue on Sunday. We are very concerned that our deep mid-April snowpack is becoming increasingly unglued, making safe travel in the mountains increasingly challenging due to the unpredictable nature of wet avalanche problems.

We’ve chosen to emphasize loose wet and glide avalanches, but other springtime shed slides should impact how and where you travel. Wet slab avalanches fail when a layer of water pools within the snowpack. Several 6" deep wet slab avalanches in the Stevens Pass area on Saturday draw attention to this concern throughout the Cascades. These avalanches could become significantly larger as the cycle progresses given numerous old weak layers in the snowpack, including the very deep mid-January interface that produced massive avalanches earlier this winter. Additionally, cornices continue to collapse during the hot weather. These could entrain snow below or trigger other avalanches. Observers reported 3 cornice fall avalanches in the Kendall Adventure zone on Saturday.

No matter what type of wet issue you encounter, the travel advice remains the same. If you choose to go into the mountains:

  •  Plan your day to travel and exit early. 
  • Give yourself plenty of options to adapt to rapidly changing conditions, including safe travel routes back to the trailhead. 
  • Pay attention to overhead slopes and choose routes that help you limit the time you spend underneath large and complex avalanche terrain. 

This is the final full avalanche forecast product of the 2020-21 season. As our capacity thins during the warmer months, please continue to share your observations and make use of our mountain weather forecasts (daily through the end of April). From all the forecasters at NWAC, thank you for all your support that makes this product possible and we look forward to resuming full operations in late 2021.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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