Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Instabilities are becoming increasingly isolated and you can find safe riding in most steep terrain.  Exceptions will be dangerously large and difficult to identify, thus careful terrain selection remains important. You can give yourself a wide buffer against the low likelihood of triggering a deep slab by riding southerly aspects or choosing routes with deep, uniform snowpacks on the shady half of the compass.  Deeper snowpacks in the Northwest Mountains are most common on leeward and wind-sheltered terrain.  Tread lightly in terrain where snowpack depths are variable from seasonal winds.    Regroup in safe zones that are appropriate for very large avalanches. 

Problemi valanghivi

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2.5–3

    Deep slabs are a low likelihood but high consequence concern on the northern half of the compass, where faceted weak layers lurk near the ground.   You are most likely to impact these layers and trigger a deadly avalanche where slabs are thinner.  Choose terrain with a deep, uniform snowpack to reduce your risk.  Be cautious in unsupported, rocky terrain or in alpine terrain where winds have created variable snow depths.  Slopes that avalanched early in the holiday cycle also have thinner slabs that could be easier to trigger.

    One of the few deep slab avalanches triggered since the New Year.  This was an explosive triggered hard slab on a west aspect at Irwin, where slab depths are variable due to seasonal wind patterns.  

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Gusty northerly winds will be strong enough to drift a couple of inches of new snow into thin wind drifts at high elevations.  These will be relatively small and harmless unless they knock you off your feet in high consequence terrain, such as above cliffs or in steep chutes.  Look for evidence of wind slab formation such as thicker drifts or blowing snow to identify the problem.

    If you see winds transporting snow like this, expect to find shallow wind slabs behind leeward terrain features.

Avalanche Discussion

The trend towards generally safe conditions continues this weekend under the current quiet weather pattern, starting with the Northwest Mountains where the snowpack is deepest and strongest.  Although we are still finding occasional propagating results in long column tests, such as a PST 35/150 END yesterday at Snodgrass, stability test scores have been improving in the past week, both locally and regionally.  That's a welcomed pattern that is further supported by a lack of obvious signs of instability or human-triggered deep slab avalanches since the big storm ended on New Year's Day.   Our forecast staff has felt comfortable stepping out into more aggressive avalanche terrain in the past week, although we still remain cautious of specific terrain features. The last explosive triggered deep slab was earlier this week, on Monday.  All of the explosive results since the New Year were in very steep, unsupported, rocky terrain or terrain with variable slab depths because of winds.  This recent avalanche in the Northern San Juans further exemplifies that type of terrain.  Terrain features where the snowpack transitions from thick to thin due to wind effects are my biggest concerns for a rare but nasty avalanche.  There are plenty of great riding options right now that avoid that kind of terrain, and with a little more time, our concerns for triggering even the most suspect slopes will diminish. For now, give yourself a margin for uncertainty and aim for terrain with consistently deep snow coverage.  Regroup in safe terrain that is out of harm's way if the whole season's snowpack releases and runs far.    

With a couple of inches of new snow yesterday in the Northwest Mountains, there is a small amount of fuel available for drifting under today's northerly winds.  Stay alert for thin wind slabs forming in alpine if you are riding in extreme terrain today.  

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