Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

UPDATE: Very dangerous avalanche conditions are expected at mid and upper elevations due to continued heavy snowfall this morning. Avoid areas where avalanches can start, run, and stop. 

The current storm will continue through Tuesday with avalanche danger in both wind loaded and wind sheltered areas.  Travel in simple terrain with less exposure to avalanches and monitor weather and snowpack conditions throughout the day. Rapid warming later this week could significantly increase danger despite calm weather.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    The strong winds and snowfall of the last 24 hours will continue into Tuesday morning. Backcountry observations from Monday are sparse, but ski areas reported large slab avalanches in wind loaded terrain with control work. Traveling in steep wind loaded terrain will probably result in triggering a wind slab, especially on unsupported features like slopes above cliffs, convex rolls, etc. Natural avalanches could still occur during periods of heavy snowfall,  higher wind speeds, or sun breaks.

    Start out the day with a conservative mindset and stick with lower angle, wind-sheltered terrain to reduce risk. Monitor changes in snow depth as you gain elevation or change aspects. Identify and avoid steep slopes that hold wind slab. Windward, scoured slopes that hold less new snow may offer safer - but not risk-free - terrain options.

     

    Rider triggered wind slab avalanche on Shuksan Arm last winter.

    Photo: Pete Durr

  • Storm Slabs

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

    Out of wind loaded terrain, there is still plenty of new snow to go around. It’s falling on a cooling trend - which makes for well bonded, right side up layers - but with 2’ on the ground plus another 1’ forecast overnight it likely needs more time to gain strength. Keep that conservative mindset in wind sheltered terrain as well until you gather information about the depth and reactivity of new snow layers. Use simple observations like test slopes in safe areas or hand shears to get a better picture of conditions. 

    If you don’t find much of a slab be prepared to see loose dry avalanches in steep terrain. On the other end of the spectrum, sun breaks could create more of a slab or initiate loose wet avalanche in steep and rocky terrain. It’s April and there is a few feet of new snow on the ground - best be ready for anything . . . . 

    Storm slab avalanche in steep, wind sheltered terrain earlier this winter.

    Photo: Stephen Semanski

Avalanche Discussion

High pressure is on the horizon as the current storm fizzles out Tuesday evening. Calm weather, blue skies, and new snow are the go-to recipe for a great day in the mountains if there ever was one. Unfortunately, strong April sun and freezing levels that shoot up to 8000-10,000' are forecast Wednesday into Thursday. Cold and deep new snow will be sensitive to the rapid increase in warming. This could significantly elevate avalanche danger at a time we usually expect it to decrease. It is still a few days away, but lookout for another spike in natural avalanche activity and very dangerous conditions later in the week.

Another avalanche problem to consider is deep slabs releasing into a layer of facets that could “wake-up” with additional load. Very large avalanches of this character were reported from the 16th through 27th of March in conjunction with various storms and then warming. All occurred in upper elevation, northerly terrain, and all but one were naturally triggered. It’s quite unlikely a single person could trigger an avalanche such as this - but there is a chance one could be provoked by a load of new or wind drifted snow, cornice fall, or another avalanche from above.

 

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