Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Rapid warming could cause natural wet loose activity and/or make slabs in the upper snowpack more reactive.   A couple of large natural avalanches ran yesterday from windloaded slopes, and numerous slabs up to several feet thick were remotely triggered late last week below treeline.  The safest riding is on slopes less than 35 degrees protected from the sun and wind-loading.   Terrain that recently avalanched all of last week's storm snow, or small terrain features with clean runouts offer lower risk options for riding in steeper terrain.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Last week's storm formed slabs up to several feet thick over faceted weak layers.  Remote triggers and natural avalanches failing on these persistent weak layers have been gradually diminishing since widespread activity peaked last Wednesday.  The greatest number of avalanches have occurred on easterly-facing slopes where faceted crusts exist. Similar structures are also found on westerly-facing slopes. On northerly-facing slopes, these slabs formed over a layer of near-surface facets.  Slabs are larger and may be more sensitive at higher elevations due to ongoing wind transport.  In a few cases, avalanches have stepped down into older weak layers much deeper in the snowpack, causing destructive avalanches.  

    Early warning signs for this avalanche problem are rare and feedback is infrequent. You can reduce your chance of triggering this avalanche problem by avoiding recently wind-loaded terrain or slopes where the snow surface is getting hot and sticky.  Safer riding is on wind-protected, sun-protected slope angles less than 35 degrees, without steeper slopes above. 

    Numerous widely propagating slab avalanches on Purple Ridge ran last week during the storm on faceted crusts.  Avalanches like this can still be triggered today.

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Yesterday's moderate west to northwest winds formed sensitive wind drifts mostly at higher elevations.  Despite limited visibility, a couple of natural and triggered wind slabs were reported yesterday.   A triggered avalanche in recently drifted terrain could step down and trigger a much thicker and wider persistent slab.  You can avoid the problem by traveling where the snow is protected or eroded by winds. Cracking in the snow or blowing snow are signs of instability.  

    Fresh debris in Red Lady Bowl, likely a wind slab that ran 3/27.  

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Strong solar radiation and warming temperatures will destabilize the snow surface on steep, sunbaked slopes, and could cause natural wet loose activity.  Watch for rollerballs, pinwheels, or active sluffing to alert you to changing conditions.  Although most wet loose activity should be small, sluffs can pack enough punch to injure or bury you in a terrain trap.  Long, steep terrain could produce larger sluffs.  There is also concern for natural wet loose activity to trigger a much larger persistent slab.  Consider your overhead hazards if wet loose avalanches start happening.  

Avalanche Discussion

Despite limited visibility, yesterday's observations include a fresh persistent slab that failed near the ground on a drifted slope on Whetstone, along with a couple of wind slabs (Emmons, Slate). Ongoing wind transport over the past few days has kept the threat of both wind slabs and persistent slabs elevated on drifted slopes.   Other notable activity from wind-loaded slopes include this 2000' wide crown that ran over the weekend near Marble, this trio of very large avalanches triggered remotely in the Anthracites on Saturday, and this huge avalanche in Barcelona Bowl that ran during the big storm last Wednesday.  

Another curveball with today's conditions is the return of the late March sun along with temperatures warming towards freezing today.  Following the last two atmospheric river events earlier in March, we saw some unexpected natural and triggered activity during the first warm, sunny day after the storm cleared.  We have some uncertainty on how today's weather will influence conditions; the warmup isn't as pronounced and there has been a longer lag between last week's major storm and today's warmup.  Given how active our persistent slabs were last week, I'm erring on the side of caution and bumping the danger back up to Considerable near and below treeline to monitor for naturals and see how today plays out.  Several avalanches a couple of feet thick (D1 to D2) were remotely triggered below treeline in the past few days (Example A, Example B, Example C, Example D). The most active aspects for persistent slabs - the eastern quadrant- will see rapid surface warming and the threat of wet loose activity that could act as natural triggers for persistent slabs.  

Today's warmup complicates an already-challenging snowpack that has produced numerous surprises and accidents in the past couple of weeks.   It might finally feel like spring again today, but the snowpack still thinks it's winter.  Get out and enjoy the nice weather, but use patience and caution with your terrain selection and suspicion with your snowpack assessments.

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