Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

The possibility of triggering a very large avalanche warrants caution above treeline. Smaller slab avalanches in new and wind drifted snow and even wet avalanches could all be confronted as well. Stay in simpler terrain to mitigate uncertainty.

Update @ 7:45:  NTL rating raised to Considerable - there will be a greater chance of triggering new wind slabs as the wind becomes stronger through the day

Avalanche problems

  • Storm Slabs

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

    Though many of the day-old storm and wind slab layers have become stale and unreactive, new layers are building on top of the old. 8” of new snow fell at Heather Meadows this afternoon and expect to see a few more through Friday. Deeper slabs likely exist in wind loaded terrain. Expect higher danger where you find extensive wind transport. You are more likely to encounter avalanches during periods of intense snowfall, warming, or rainfall. 

    Track the depth of new snow as you gain elevation or change aspects. Find test slopes in safe areas to see how the new snow layers react.  Visual clues like blowing snow, cornices, and wind scoured snow surfaces will point towards areas of wind loading. Hand shears can help you track changes in layering and bonding as you travel. When in doubt stick to lower angle, simpler terrain to reduce risk.

     

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Very large natural and artificially triggered avalanches were reported on Wednesday. They failed in a layer of weak facets buried on March 8th. Though there is a low likelihood of triggering one of these monsters the results would be deadly if you did. A large load like a cornice fall, smaller avalanche initiating in higher terrain, or a group of people on a slope could trigger one where a single person might not. Observations of these and other avalanches with unusual characteristics are grounds to consider taking a big step back in terms of terrain. Though they are most likely in upper elevation terrain on northerly aspects, two of them occurred on slopes facing more east than north. This isn’t really a “manageable” avalanche problem that can be figured out and mitigated with snowpits and other assessment tools. You are either in the terrain where it could happen or you are not. If you chose to travel these areas you are simply accepting a higher risk of triggering a very large avalanche.

     

    (3/16/2022)

    A very large avalanche triggered on the Shuksan Arm with control work.

    Photo: Adam Ü

Avalanche Discussion

In addition to the above mentioned problems, wet loose avalanches in some form are a near daily occurrence given the transition to spring. Expect to see them at lower elevations, especially if snow levels are higher than forecast, or at all elevations with strong sun our greenhousing. 

Despite near freezing temperatures Wednesday, warming from the sun and greenhousing affected most snow surfaces save for upper elevation, northerly terrain. This crust now has 10-20cm of new snow on it as of Thursday evening. Below the crust there is 60cm of right side up storm snow in wind sheltered locations. Wind loading created slabs of 120cm or deeper. On solar aspects the storm snow sits on a stout sun crust and informal testing showed good bonding on unsupported test slopes prior to warming. On shaded slopes the new snow sits on thin, weak crust. Below there is a pencil hard wind slab and then a 1F faceted layer down to the Early March Crust.  This faceted layer is likely the root cause of the large avalanches reported on Wednesday.

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