Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

New snow and moderate winds will increase avalanche danger in wind exposed terrain, especially in the alpine. Identify and steer around recently wind loaded features and retreat to simpler, sheltered terrain if conditions deteriorate.

Lawinenprobleme

  • Wind Slabs

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

    Wind slab avalanches near and above treeline will be the greatest hazard to backcountry travelers on Sunday. Though new snow amounts are uncertain and could vary greatly across the zone (more in the north, less in the south), there should be enough to create fresh wind slabs on lee slopes. Wind speeds - and wind slab formation - could increase in the afternoon as the storm intensifies. 

    In addition to the usual instability that comes with new wind slabs, the variable old snow surface of slick crusts, facets, and occasional surface hoar will add a layer of uncertainty. On some slopes wind slabs may bond well to the old snow surface, on others not so much. Test slopes, hand pits, and other snowpack tests will provide useful information, but the bond of new wind slabs to the old surface could be very different a short distance away.

    In addition to clues like cornices and differences in snow texture, note where the wind has deposited enough snow to cover the old, rough surface features from rain, avalanches, melting, wind, etc. If poor visibility, strong winds, or heavier than expected snowfall make it difficult to assess conditions, consider avoiding all wind loaded avalanche terrain until conditions improve.

     

     

    An example of a wind slab avalanche showing active loading and chunks of stiff wind slab debris.

Avalanche Discussion

An extended period of rain, then high pressure and warm temperatures, is finally ending as low pressure approaches from the northwest. The variable weather created a mix of snow surfaces that differ by aspect and elevation and even across a single slope. Slick rain crusts that actually made ski crampons useful, drifts of small faceted grains, extensive avalanche debris, sun crust - pretty much everything was out there besides cold settled powder.

The variable surface is adding to uncertainty about the bonding of new snow and wind slab layers. The greater mystery is a crust-facet combination just below the surface. In this instance, an old rain crust (buried January 6th, found 10-30cm down) has a layer of facets between it and the supportable surface crust. This crust-facet sandwich has been found throughout the Cascades near and above treeline - slopes receiving strong solar input have only a single crust at the surface.

This setup brings with it a high degree of uncertainty as it could do nothing or create big avalanches. While areas farther north in the Cascades may get enough load with this storm to give this layer a good test, areas farther south and east may have to wait. Either way, it requires a conservative, wait-and-see mindset to safely figure out if this not-so-savory sandwich will be a passing fad or with us for some time.  

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