Avalanche forecast

West Slopes South

Northwest Avalanche Center
View on map

Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Weather conditions and avalanche danger will vary across West South on Friday - stay alert to changing conditions. Expect greater danger on the volcanoes where more snow is expected. A possible switch from snow to rain will increase the chance of wet avalanches, especially farther south in the zone where this is more likely to occur.

Avalanche problems

  • Wind Slabs

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

    Strong winds formed hard new slabs that could still be reactive on Saturday. More snowfall and moderate to strong winds will likely build new slabs as well. Use scoured snow surfaces, changes in snow stiffness, and signs of recent avalanche activity to identify where wind slabs could lurk. Use small steep slopes and other informal tests to check the bond of wind slabs to the layer below. You can also just bypass steep wind loaded slopes and features by utilizing lower angle, more planar terrain. Steer around slopes where you observe active wind loading. 

    (12/22/2022)

    Natural wind slab avalanche in the Crystal backcountry. Note small cornices and rounded, smooth drifts on and below the ridgeline in the background.  These are telltale indicators of recent wind loading and wind slab formation. (HS-N-D1.5-R1-S) NW @ 6000'.

    Photo: Dallas Glass

  • Storm Slabs

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

    Snowfall with warming temperatures is on tap for Friday. This will likely build dense new slabs over cold, weak snow currently at the surface. Recent snow layers rest on a layer of surface hoar or weak facets in some areas as well. 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.

     

    Small storm slab avalanche in Snoqualmie Pass.

    Photo: NWAC Public Obs

Avalanche Discussion

Observers in the Crystal backcountry reported extremely cold and windy conditions Thursday. Widespread wind transport was noted down into below treeline areas. Informal testing repeatedly produced shooting cracks and small slab avalanches were very easy to trigger. Natural wind slab avalanches to D1.5 were also reported.

Storms earlier this week put down 10-20” of new snow across West South. 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. Other than a single avalanche triggered by mitigation work at White Pass, no other avalanches involving these buried layers were reported in West South. More avalanche activity and observations pointing towards instability were noted in other zones.

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.

Regions covered