Bulletin d’avalanche

West Slopes Central

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

You could trigger large, dangerous avalanches in above treeline terrain. A lot of uncertainty exists as to how reactive the weak layer is, but for now avoid areas where we've encountered the problem- large, steep, unsupported above treeline slopes. There's a chance that the snow which falls during the day could develop into small reactive pockets at upper elevation, or run as small wet avalanches at lower elevations. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    The West North Zone had large, deep avalanches occur with control work, and NWAC Forecaster Lee Lazarra also saw some natural ones which probably occurred on the same weak layer.  The avalanches are occurring just above a crust, and a faceted weak layer could exist, although it has not yet been confirmed. The West North Zone's conditions are similar to much of the northerly half of the West Central Zone. With the recent avalanches we're seeing, it is enough information to tell us that you could trigger a very large and unsurvivable avalanche in the backcountry on Thursday. 

    These avalanches are occurring on large, steep, unsupported slopes in above treeline areas. Until we know more about this problem, consider avoiding the previously mentioned slopes where they are greater than 35 degrees.  An unsupported slope refers to a slope that rolls over into steeper terrain, lacking an abrupt transition to lower angle terrain beneath that steep rollover. Pay attention to the usual signs of unstable snow such as cracking and whumphing, but these indicators are probably not signs that you will find before triggering one of these deeper avalanches. A couple inches of snow will fall during the day, and increasing wind may lead to small fresh slabs of snow.  It also may be the case that you could find wind slabs in the southerly portion of the zone and in areas closer to Steven Pass. 

    (3/16/2022)

    Two natural slab avalanches on in the West North Zone. Suspected of naturally triggering with rapid warming Wednesday morning. Wet loose in the surrounding terrain may have triggered the lower avalanche. East aspect at ~6000'.

    Photo: Lee Lazzara

  • Loose Wet

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

    Wet loose avalanche activity occurred Wednesday, affecting the previously dry snow that fell Monday night into Tuesday. Especially in the northern half of the zone, surfaces were probably moist and saw avalanches on all aspects due to cloud cover trapping heat and moisture in. Looking into Thursday, we do not expect to see as much avalanche activity, but we may see some. Especially in spring, it's tougher to predict how much wet loose activity we'll get. Surfaces that were already moist on Wednesday will not react as easily. Wind may also keep surfaces cooler. Any avalanches will probably occur only in the small amount of new snow that falls during the day, as the previous layers already moistened.  If you encounter wet snow and rollerballs or small loose avalanches, consider avoiding similar steep slopes. 

    (3/14/2022) Small loose wet slides seen in the last few days, similar to what you might see at lower elevation on Thursday.  Photo: Matt Primomo

Avalanche Discussion

If you're heading out into the West Central Zone, take a look at the neighboring forecast zones, as information is limited in this zone.  Lower elevations are losing snow quickly, and you might not find any snow until you reach about 3000ft now. These springtime conditions and rapid melts are making travel more challenging at lower elevations, so prepare for this on your travels Thursday. 

Régions couvertes