Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Greater avalanche danger is found anywhere the wind transported light new snow into unstable slabs. Steer around steep slopes with recent wind loading on lower-angle terrain. Deep snow hazards still exist, especially where you could fall into a tree well or some other terrain feature. Stick with your partners and keep them in sight at all times.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    The latest east wind event met expectations with some areas seeing minimal wind effect while nearby terrain got hammered. The most hazardous conditions are found in alpine terrain that holds the largest slabs. The distribution and reactivity of unstable wind slabs will vary across the zone. Evaluate terrain on a case-by-case basis - some slopes could be just fine with others a definite no-go. 

    Look for recently scoured ridgelines and other wind affected features to identify the pattern of wind loading in the terrain around you. A few inches of new snow could obscure some of these clues. Test slopes and hand shears will help gauge wind slab reactivity and depth and can help you identify areas where they are easier to trigger. 

    (2/22/2022)

    Wind slab avalanche last season between Table Mt. and Ptarmigan Ridge in the Baker Backcountry. Southwest aspect @ 5000'.

    Photo: NWAC Public Obs

  • Loose Dry

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

    The new snow is becoming more cohesive but you could still see some sort of new snow avalanche in steep, wind sheltered terrain. These kinds of avalanches are the easiest to anticipate. If you get into steep terrain some amount of snow will probably come down the hill with you. 

    Also, look out for shallow slabs forming at the surface if loose snow becomes cohesive during sun breaks or with more warming than expected. If the sun comes out with any force it could also trigger a round of loose wet avalanches - keep an eye on sunny slopes overhead.

    Example of dry loose avalanches big enough to knock you down and take you for a short ride.

Avalanche Discussion

Reported avalanche activity was not widespread despite the quantity of new snow, but was observed where the wind thickened up the snow to make more of a slab. The east winds really made an impact at Snoqualmie Pass where widespread wind transport and plenty of reactive but small wind slab avalanches were reported.  A bit less wind transport was observed at Stevens Pass with dry loose avalanches being the main danger in sheltered areas.

The White Chuck Tripod near Darrington recorded wind speeds of up to 15mph. While this seems pretty insignificant, this weather station - established primarily for snow depth and temperature observations - sits in a very, very sheltered location. If it shows any wind then it's definitely blowing. If wind speeds are up in the teens then it's probably nuking and wind slabs built from plentiful, light density new snow are nearly guaranteed.

In West North natural avalanches which released during a period of stronger winds Friday evening were observed on Table Mt. Also, human triggered avalanches were reported from around the Baker Backcountry, generally D1 in size and triggered on short, steep, unsupported features. The most notable avalanche was triggered by a cornice fall Saturday afternoon (photo). No observations were reported from other areas of West North.

All of these avalanches highlight the current snowpack challenge:  the deep new snow is itself fairly stable other than loose snow avalanches, but if wind, sun, or warming have any meaningful impact at the snow surface than the likelihood of seeing or triggering an avalanche increases quickly. It also reminds us that cornices are big, becoming unstable, and are a consideration in backcountry travel for the rest of the winter and spring.

 

 

Régions couvertes