Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The greatest hazard is steep slopes holding wind drifted snow. Be alert to terrain features with active wind loading or smooth-looking drifts. Stiff and hollow-sounding snow is another sign you are in an area where you could trigger a slab avalanche. Avalanche danger is generally low in the north of the zone and increases as you move south to areas that received more new snow last week.

Avalanche problems

  • Wind Slabs

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

    Wind slabs should present as stiff, smooth snow, often with scoured snow surfaces found upwind or on the other side of a ridge. Look for “fat” drifts that might also feel firm and hollow. 

    Wind slabs could be more reactive when perched on slick sun crust or unsupported, convex breakovers. The sweet spot might be slopes with recent wind transport that are still sheltered enough for snow to drift and accumulate. 

    Hard wind slabs can break in unpredictable ways, sometimes above you or after several people have crossed a slope. You can evaluate wind slab bonding to layers below or just navigate around steep wind loaded slopes to avoid the problem.

    (1/30/2023)

    A natural Wind Slab avalanche was observed on Mount St. Helens on 1/30. Note the convex slope and nearby rocky terrain. [HS-N-D2-R2-I SSW 4500’]

    Photo: NWAC Forecasters

Avalanche Discussion

If the sun breaks out Wednesday you might see minor signs of instability like rollerballs or very small wet loose avalanches in areas that received new snow.

Observers at Crystal reported 1” of new snow transported by stout westerly winds Tuesday. New drifts formed but there just wasn’t enough raw material to build a legitimate wind slab in the terrain observed.

An NWAC Forecaster team traveled to Mt. St. Helens Monday. Wind affected surfaces were found in most open terrain while upper elevations were scoured down to a firm layer. They triggered multiple test slopes at mid elevations and observed one large natural avalanche (HS-N-D2-R2-I SSW 4500’) that had failed within the last 24 hours. 

They unintentionally triggered a large wind slab avalanche (HS-ASu-R2-D2-I S 4000') 150’ wide with a crown up to 3’ in depth. It failed on the Jan 21st interface - sun crust on this aspect - which is now found 1.5’ deep. It's suspected to have failed at the same interface as this avalanche on Jan 22nd. While no one was caught, it was triggered remotely from the flank while bypassing the steeper slope on lower-angle terrain. 

Over the weekend observers at White Pass and Rainier reported seeing and triggering small wind slabs. Firm, scoured surfaces were found at upper elevations while moderately sheltered areas held hard slabs that were reactive to human triggers.

Our primary concern is wind slab layers but we are still keeping an eye on weakening (faceting) layer interfaces found at and above the MLK crust. Though currently not an issue, they are layers to track going into future storms.

Regions covered