Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering avalanches is still possible in wind drifted snow above treeline. Steer around steep terrain holding slabby-looking drifts.  Look for these below ridgelines and around other features that catch snow.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Light precipitation and strong winds will continue to build wind slabs in alpine terrain. The current surface of dense snow and sun crust limited the snow available for wind transport in the past 36 hours. Snowfall is needed to provide more raw material for new wind slabs. The exception is in the highest elevation terrain where you could find deeper, larger wind slabs.

    Track the pattern of loading and scouring as you gain elevation to identify slopes with wind slab. Trigger points could include steep convex rolls or steep terrain around cliffs and other rocky features. Use simple tests in safe areas to see how well these slabs are bonded to layers below - or simply bypass steep wind loaded features on lower angle, planar terrain.

    Blowing snow and fresh cornices like this can indicate wind slabs may exist on the slope below. Photo: Andy Harrington

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    There is still a low likelihood of triggering an avalanche in crust-facet layering from late January. Factor in the following if you are planning to get into alpine terrain in the next week.

    • The snowpack structure is inherently weak.
    • The layers are still reactive above 5000’ on aspects that did not receive strong sun in late January.
    • Reported natural and human triggered avalanches occurred at the same aspects and elevations.
    • They mostly occurred where there are 2 or more feet of new snow over the crust-facet layering.
    • Snowpack tests produce inconsistent results at the crust-facet layering, sometimes even in the same snowpit.
    • Many steep slopes - some very near avalanches that released in the same layers - have been ridden and skied with no results.

    The conclusion so far is that there are very few places where you could trigger one of these avalanches, but it would also not be surprising if another one was reported this weekend. If you venture onto steep terrain in these areas you are assuming a bit more risk than if the layering was not present.

     

Avalanche Discussion

No new avalanche activity - or even much in the way of mountain travel - was reported on Tuesday.  Observers on Monday found wet snow up to 4500' with a supportable crust from that elevation to treeline in West Central. No wet avalanche activity was observed. A very intact crust-facet sandwich was found in the same area at 5000' on a west-facing slope.  Snowpack testing produced positive results with ECTP's and a PST 40/100 (end). 

After yet another weak system on Wednesday, high pressure, sunny skies, and much higher freezing levels are expected in the second half of the week into the weekend. A corresponding increase in danger from wet avalanches is anticipated as well. 

Regions covered