Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

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

A dynamic weather forecast will require continual assessment of avalanche danger in the specific area you travel. Increasing snowfall at warmer temperatures, gusty alpine winds, and uncertainty about the switchover from snow to rain warrant a conservative mindset and plan for the day. 

Update @ 8:26am:  BTL danger raised to Considerable due to warmer temperatures and greater precipitation initiating natural wet avalanches at all elevations.

Avalanche problems

  • Storm Slabs

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

    Snowfall with warming temperatures and strengthening ridgeline winds are on tap for Friday. This will likely build dense new slabs over cold, weak snow currently at the surface. In exposed terrain steer around slopes where you observe active wind loading. In all areas look for upside down snow, shooting cracks, and small natural avalanches. Move to simpler terrain if storm slabs become more reactive and dangerous. A small avalanche could trigger a bigger one releasing in deeper layers.

    You will see loose wet avalanches if it starts raining or temperatures are warmer than expected. The transition to rain is uncertain and may not happen until Friday evening or Saturday.  Get out from under steep terrain if you observe rain, snow sluffing off trees and rocks, and other signs of instability related to warming. Natural wet avalanche activity isn’t far behind.

    Example of widely propagating storm slab avalanche in sheltered terrain.

Avalanche Discussion

Observations varied in surrounding zones Thursday. To the north, wind affected snow continues to be found in exposed terrain but no wind slab avalanches were reported. No whumphing was noted even though buried surface hoar continues to be found below the most recent snow in wind sheltered areas. Greater wind transport was noted in Stevens Pass and another large whumph was reported from sheltered terrain - buried surface hoar is again the likely culprit. Extensive wind transport at all elevations and small but very reactive wind slabs were reported to the south. Natural wind slab avalanches to D1.5 were also reported.

Storms earlier in the week put down 10-20" or more of cold, light density new snow across the zone. The new snow and wind slabs formed over a variety of old snow surfaces, most notably surface hoar and weak, faceted grains that formed and survived at or near the surface during high pressure last week. The lack of avalanche activity is itself a significant observation. It shouldn’t distract from the fact the Cascades have experienced colder than average temperatures and snowfall resulting in a snowpack with lingering weak layers. This should keep our attention despite the lack of widespread avalanche activity. This is especially important with the transition from the current temperature regime to warmer, wetter, and more active weather in the week ahead. A large avalanche cycle over the weekend is not certain, but there is a better chance of seeing one than in recent weeks.

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