Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

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

Kernpunkte

Expect to find sensitive wind-drifted slabs at upper elevations that increase in size and sensitivity to human triggers throughout the day.  Strong westerly winds may form slabs in open areas below treeline.  On some slopes, an avalanche in the storm snow could trigger a deeper slide on older layers.  You can reduce the likelihood of triggering an avalanche by avoiding leeward terrain and favoring wind-sheltered slopes.  If you experience collapses or cracking in the storm snow head to lower-angled terrain.

Lawinenprobleme

  • Wind Slabs

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

    Wind direction began from the southwest yesterday afternoon and slowly transitioned to the west last night.  On Friday, the wind will make a final shift to the northwest.  The transition of the wind throughout the storm will spread Wind Slab formation to an increasing number of aspects.  Expect to find Wind Slabs in many leeward terrain features at upper elevations, but you may find them at lower elevations in open areas.  Wind Slabs often feel stiffer or denser than the storm snow in protected areas.  A triggered avalanche in wind-drifted storm snow could release an avalanche deeper in the snowpack, particularly on aspects highlighted by the Persistent Slab rose.

    This 2-foot thick wind slab was remotely triggered near Hunter Hill on 3/28.  

  • 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 over a week ago.  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 which should be bonding better now.  Slabs are larger at higher elevations due to previous 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 wind-loaded terrain and unusually shallow terrain.  Safer riding is on wind-protected terrain less than 35 degrees, without steeper slopes above.

    This large persistent slab ran naturally on the afternoon of 3/28 on Schuylkill Ridge.

Avalanche Discussion

As of 4 am, storm totals range from 3 - 7 inches across the forecast area with the deepest totals found in the Northwest Mountains.  Snow and strong westerly winds are forecasted to continue throughout the day.  Some areas may accumulate over a foot of new snow by sunset.  Expect Wind Slabs to grow in size throughout the day and spread to more aspects as the wind direction transitions from the southwest to west to northwest by the afternoon.  Weather conditions clearly point to sensitive avalanche conditions on leeward slopes.  You are likely to trigger an avalanche in the storm snow on drifted terrain features.  Natural avalanche activity is possible on well-drifted slopes.

A forecaster observation from yesterday found faceted snow grains resting above crusts on east and northeast aspects below treeline.  This suggests the storm snow will not bond well to the old snow surface on sheltered below treeline slopes.  As storm snow accumulates today, the potential for human-triggered avalanches will increase in sheltered terrain, particularly where you find about 10 inches or more of new snow.  If you are riding in sheltered areas, keep a close eye on the increasing storm totals throughout the day and look for signs of instability like cracking or collapsing to indicate worsening avalanche conditions in sheltered areas.  Small test slopes will be useful in gauging the bonding between the new and old snow.  If you experience signs of instability then move to sheltered slopes 35 degrees or less.

There is the potential for avalanches to break several feet below the recent storm snow.  The Persistent Slab problem is most likely to be found on drifted terrain features near and above treeline.  Avalanche activity from the past few weeks suggests that faceted crusts buried several feet deep are the most likely place for failure.  The Wind Slab avalanche problem overlaps with the most concerning aspects on the Persistent Slab distribution rose. Triggering an avalanche in drifted storm snow could release a deeper avalanche.  Your best defense during this loading event is to avoid drifted terrain which simultaneously reduces the chances of triggering an avalanche in the storm snow as well as deeper weak layers.

The snowpack remains in a winter-like state with a variety of persistent weak layers on many aspects.  Even though the calendar suggests spring, the snowpack feels very wintery.  Spring weather will arrive at some point and improve avalanche conditions, until then remain patient.

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