Bulletin d’avalanche

Central Cascades

Central Oregon Avalanche Center
Voir sur la carte

Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
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

Monday will be a tricky day in the backcountry.  It will be possible to trigger a large avalanche on weak layers deep in the snowpack.  Take extra time to develop confidence in the snowpack, and be conservative.  Many of the tools and observations that we typically use for Wind Slabs and Storm Slabs will not provide pertinent information for the Persistent Slab problem.  Be wary of steep, unsupported slopes.

Problèmes avalancheux

  • Wind Slabs

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

    On Sunday I observed relatively minimal wind slab formation near treeline at Tam MacArthur Rim.  Other regions like Santiam Pass were recording Strong winds from the East.  Perhaps more pertinently the wind forecast for Sunday night and Monday is for Moderate speed wind from the southeast, south, and southwest.  There is a lot of snow available for transport in addition to any new snow that falls overnight.  Watch for cracking in more cohesive snow that is directly below ridgelines as well as evidence of scouring and blowiing snow on windward slopes (if the snow has been blown off a slope, it has probably been blown onto the opposite slope).

  • Storm Slabs

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

    On Sunday many Storm Slab avalanches to size D1.5 were observed at Tam MacArthur Rim.  All of the ones that I observed occurred in the most recent storm snow.  Storm Slab instabilities usual dissapear in a day or two, but Monday is too soon to remove them from the forecast.  Be aware that these smaller avalanches could step down to the deeper weak layers in our snowpack.  Small, steep, convex test slopes can give you the best information regarding this avalanche character.

    (2/18/2024)

    Test Slope at Tam Rim, north facing below treeline

    Photo: Gabriel Coler

  • Persistent Slabs

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

    Peristent Slab avalanches will pose the greatest danger to riders on Monday because they will be less predictable and large.  Early in the weekend several avalanches were triggered that failed on a layer of 1-2 mm facets above the prominent rain crust (approx 80 cm down).  Smaller, more likely Wind Slabs and Storm Slabs could step down to this deeper layer in our snowpack.  This is a good time to avoid steep, unsupported slopes and trigger points.  Whumphing and collapses in the snowpack are often signs of a Persistent Slab avalanche character.

Avalanche Discussion

Avalanche activity associated with the new snow continued into Sunday.  We have received 2 ft. or more of new snow since last Wednesday morning.  The prominent rain crust is buried about 80 cm.  Some of the recent avalanche activity occurred on a weak layer of facets just above the rain crust.  Today I didn't observe test results that would be indicative of avalanches on this layer, but Elliott was finding propogation in his ECT tests yesterday, and there were observations of collapses at Black Crater.  Compression tests are a good tool for observing these deeper layers, but don't let a few test results convince you to ride more aggressively than better judgement would dictate.

Régions couvertes