Bulletin d’avalanche

East Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Wed
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

A significant storm will bring snow and winds to the Cascades, creating very dangerous avalanche conditions. With the added load to an already weak snowpack, we expect very large avalanches to be very easily triggered and may run naturally. Avoid all avalanche terrain, and be knowledgeable of the terrain above you, as avalanches may run into lower elevations from above.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    If we haven't already reached a tipping point, a storm bringing 8-10" of snow with strong winds will push the snowpack over the edge. Triggering large persistent slab avalanches that break widely 2-4ft deep will be very likely, and we expect natural avalanches may run on these deeply buried weak layers as well. These avalanches may propagate widely across entire bowls and ridgelines. The most concerning slopes will be at mid and upper elevations, particularly in leeward terrain where the winds drift the snow deeper. With this rapid loading event, you should treat any steep slope as suspect. Avoid traveling on or under steep terrain. Choose low-angle slopes well away from the runouts of large avalanche paths. Since last Friday, there have been six close calls and one fatality involving this layer of weak-faceted snow over the Early February Crust. Many of these observations indicate that the terrain had already been skied/ridden once or multiple times before the avalanche occurred. It might not even be the first person on the slope that triggers the slide. While this reactivity is unusual for Washington, it is typical for this avalanche problem. This problem requires patience, conservative terrain selection, and maintaining wide margins between you and steep overhead terrain.

    (3/2/2024)

    You can still trigger very large avalanches like this example from last weekend.

    6600 ft on a NE aspect on Darland Mtn. 

    Photo: Katie Warren

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    The storm may bring up to 10" of new snow to the zone. This snow will fall on variable surfaces, including slick crusts, weak faceted snow, and surface hoar. These old surfaces may form a weak bond with the new snow and avalanches may be easy to trigger. Moderate to strong winds accompanying this storm will form deep wind slabs near ridgelines, the base of cliffs, and steep gullies. Trigging a small storm slab could result in a much larger persistent slab avalanche releasing. Choose very conservative terrain in forested areas and avoid slopes over 30 degrees. 

    Elevations below about 4000ft have little new snow over a thick crust and will likely have much less potential for large avalanches. 

    (1/7/2024)

    Small test slopes are a great way to test for storm or wind slab instabilities. Unfortunately, they aren't reliable for more deeply buried and persistent avalanche problems. 

    Photo: Joseph Labernik

Avalanche Discussion

NWAC will be closed on Tuesday, March 12th, as we gather and grieve following the death of one of our forecasters, Matt Primomo. We will not issue regular avalanche or mountain weather forecasts on Tuesday. We will return to normal operations on Wednesday, March 13th. We appreciate the community's understanding and support during this time.

Discussion:The heaviest snowfall will occur overnight, but winds will continue into the day on Tuesday. With this active persistent slab problem, give extra wide margins in your routes, steering far away from avalanche terrain.

Outlook (Day 2): While we expect natural avalanche activity to taper off by Wednesday, the snowpack will hang in a delicate balance and may be ripe for human triggering of very large avalanches. Sunshine and warmer temperatures will also add to this messy situation with the potential for large wet loose avalanches on southern aspects. 

This pattern of persistent slab problems can be challenging for backcountry decision-making. It takes conservative terrain management and diligent patience. Stepping into steep terrain at mid and upper elevations is simply just a game of chance; you may get away with it, or you could trigger a very large avalanche that is likely to injure or kill you. The structure is especially apparent in the eastern Cascades, where the snowpack is generally more shallow than at the crest. So, if you're venturing into these eastern zones, be prepared to take a step back in your typical terrain selection and understanding of the snowpack.

Summary of Recent Avalanche Incidents: As recently as Saturday, a skier triggered a very large (D3) avalanche in the Teanaway. The skier was caught and carried nearly 1000 vertical feet but miraculously came to rest uninjured on the surface. On Thursday, snowbikers remotely triggered two very large avalanches in the Teanaway, and there was a close call with a skier who was caught and carried in an avalanche on the S aspect of Van Epps Peak. Earlier in the week, snowmobilers triggered large avalanches around the Blewett Pass area, and a skier was partially buried with minor injuries in an avalanche on a NW aspect of Jim Hill in the neighboring Stevens Pass zone. Last Saturday, there were two separate incidents near Darland Mountain. One avalanche resulted in a close call, but unfortunately, in the other, a snowmobiler was fully buried and did not survive.

You can add to the avalanche forecast. Submit your observation here.

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