Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Warming temperatures should create unstable snow as the daytime progresses. Wet loose slides may run naturally, and become larger on very steep slopes at mid elevations. Cornices may begin to fall, and they could trigger larger slab avalanches on buried weak layers. 

Avalanche problems

  • Loose Wet

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

    As temperatures continue to climb, snow surfaces should become wetter. Wet loose avalanches should continue to grow larger as the day warms up. Signs of wet loose avalanche activity are rollerballs, and fresh fan-shaped avalanches with chunky looking debris. You can also look for active shedding of snow off trees and rocks. Slides may occur on all aspects at mid and lower elevations. Theres uncertainty with the cloud cover forecast, but if the sun comes out strong than expect activity to increase. Loose wet slides could run far in very steep locations, and they could pull out wider slabs in some cases.

    Stay off of, and out from underneath very steep slopes once the daytime warmup begins. Keep in mind overhead avalanche paths, especially those that catch direct solar radiation, as these may warm faster. Upper elevation, north facing slopes may be spared the warming, but that remains to be seen.

    Loose avalanche in moistening snow.

    Photo: Matt Primomo

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Cornice hazard should begin to increase with the sustained warm temperatures. Cornices are large, and may begin to sag and fail. Any large cornice falls could be dangerous in their own right, and they could also trigger deeper avalanches below. Attempt to minimize your time underneath the honkers, and don't be afraid to steer widely around potential runout zones.

    Wind slabs could still be a concern at the highest elevations in the shade, so continue to assess for cracking in wind textured snow. Look for shooting cracks in wind-thickened snow, and other recent slab avalanche activity. Some shaded, northerly aspects near and above treeline may still harbor more deeply buried faceted layers. Large triggers, such as cornices could initiate deeper slab avalanches on these layers.

    Cornices may fail, and they could trigger deeper slabs below. March 10 photo of McGregor Mtn, NNE, 7,200ft on March 10.

    Photo: Matt Primomo

Avalanche Discussion

Temperatures should continue to climb on Tuesday, and most snow surfaces will continue to moisten. Along with this rise in temperatures comes some uncertainty to how the snowpack will react, but in any case,  conditions should become more dangerous. Observers reported a few small windslabs in upper elevation terrain on Monday, and the start of our significant warmup by mid afternoon. Rollerballs, and moist sticky snow was noted on all elevations and aspects towards the end of the day in Cutthroat. On Sunday, observers reported a handful of small (D1) wind slab avalanches in alpine and treeline terrain, and one small (D1) loose wet avalanche below treeline near Cutthroat. On Saturday, observers triggered loose snow avalanches and a small wind slab avalanche on a northeast aspect near Harts Pass. The storm of the 14-15th delivered over 1-2 feet and brought an active day of natural and triggered avalanches. On wind-sheltered NW-NE aspects near and above treeline, you can find a thin layer of near-surface facets 1-2 feet below the surface and often on a crust. This layer (buried on March 8th in other zones) has been the source of impressively dangerous persistent slab avalanches near the Mount Baker ski area and other parts of the Cascades.

A deeper persistent weak layer still exists in the zone. The layer can still be found about 3 feet deep, sandwiched between eroding crusts on NW-NE aspects near and above treeline, and has been particularly problematic in the Harts Pass area. The most recent of these was triggered on March 9th in Allen Basin. While triggering an avalanche on this layer (the late January facets) is unlikely, the consequences could be serious. You can limit your exposure to shallow, rocky areas, and very steep and unsupported slopes. After a widespread avalanche cycle on 2/28-3/1, observers reported a number of deep crowns and avalanches throughout the zone that likely ran on the weak layer. See the avalanche occurrence database for more details.

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