Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 5 months ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Snow and wind drifting are increasing the avalanche hazard.  Manage for instabilities in the fresh snow, especially as you gain elevation towards deeper snow totals and more wind drifting.  Near the valley floor, shallow instabilities might plow deeper into the saturated snowpack below.   

Lawinenprobleme

  • Wind Slabs

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

    Moderate southwest to west winds have been drifting the new snow at higher elevations, forming thicker and more cohesive slabs.  Slabs of drifted snow are expected to be the most sensitive avalanche problem today, and are most likely found below leeward ridgelines or cross-loaded terrain features.  Look for blowing snow, thicker-feeling drifts, or shooting cracks to warn you of the problem.  

    An example of a wind slab from the archives

  • Storm Slabs

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

    Storm totals should exceed 18" by this afternoon.  In wind-protected terrain, monitor for instabilities in the new snow - either slabs or sluffs - running on harder crusts below.  Use small test features to assess how well the snow is bonding, and monitor storm totals to evaluate the potential size of an avalanche.  Storm instabilities will be most hazardous in very steep terrain or above terrain traps such as gullies or trees.  

    An example of a thin storm slab from the archives.  

  • Loose Wet

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

    Below about 10,000', shallow avalanches in the new snow might gouge deeper into a saturated snowpack below.  These instabilities will most likely start as moist sluffs in very steep terrain, indicated by rollerballs or pinwheels, and are caused by fluctuating rain/snow lines.  The only terrain holding onto an old saturated snowpack below the new snow at this low elevation is on northerly aspects.  

    A saturated, cohesionless snowpack exists beneath the new snow at lower elevations.  If you are able to initiate a small instability at the snow surface, it could grow surprisingly large by gouging deeper into the wet snowpack.  

Avalanche Discussion

The snowpack just spun a 180 on us, and it's time to shift mindsets back to more winter-like avalanche problems.   Below treeline storm totals this morning are typically 6" to 12" of dense snow, and should double by the end of the day. Expect lower-density snow and deeper accumulations as you gain elevation.  The Northwest Mountains are favored for the most snowfall, so you can expect avalanches in the new snow to be larger and more hazardous as you move towards the Ruby Range.  Following weeks of unusually hot weather, the storm interface is a textured melt-freeze crust on most slopes.  The new snow is expected to bond favorably with the crust, especially at lower elevations where it began warm and wet.  As you gain elevation, there's more uncertainty of how well the storm interface will bond, and as you climb into wind-drifted terrain, you are more likely to find density differences forming within the new snow that can act as weak layers.    

As seems to be the theme this winter, we find ourselves in somewhat uncharted territory, with greater uncertainty: a big loading event on a wet snowpack that hasn't seen a legitimate refreeze.  Below 10,000', the snowpack saw rain changing to snow overnight, and we might see rain levels creep above the valley floor again this afternoon.  The new snow and mild temps could insulate the wet snowpack below from even a surface refreeze, meaning a shallow instability in the new snow could gouge deep into the wet snowpack.  Climbing to an elevation where you find a crust below the new snow will resolve this issue.   As you gain elevation, we can't completely rule out the possibility of a deeper wet slab that releases from today's additional loading, similar to this avalanche last season.  Water has drained through basal weak layers on most slopes by now, but a few might retain enough liquid content and grain weakness to cause a surprisingly large slab failure near the ground.   This seems like a very low-probability event, and one that would be quite difficult to assess.  

Events: Join us Friday, April 3, at the Talk of the Town from 5-8 p.m. for our Party for the People. We will have live music from CBAC house band Deep Slab Instability and beers are on us. It’s our way of saying thanks for all of the support again this year!

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