Bulletin d’avalanche

Lizard-Flathead

Jan 13 – 14, 2018Avalanche Canada
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Archivé · expiré 9 years ago

Danger d’avalanche

Mon
Tue
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

A Special Public Avalanche Warning is in effect for this region. With a tricky snowpack and large avalanches triggered on low-angled and treed slopes Travel In Avalanche Terrain Is Not Recommended.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–4
    Large avalanches are being triggered on buried weak layers, even in fairly dense trees and shallow slope angles, including remotely triggered slides. These layers are touchy and can produce very large, destructive avalanches that run far.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3
    Many avalanches have been naturally and human-triggered in the recent 100+ cm of snow. Incoming warm air temperatures should increase the likelihood of triggering. If triggered, storm slabs could step down to deeper persistent weak layers.

Confidence

High -

Weather Forecast

Saturday and Saturday Night:  Cloudy, flurries, little wind ... not much of significance ... however a warm ridge is approaching which means a temperature inversion with warm temperatures at treeline and alpine elevations will devolop over the next few days.SUNDAY: Mix of sun & cloud and the temperature inversion could mean valley fog with sunshine above. Treeline and alpine temperatures just below zero. Light northerly winds.MONDAY: Mostly sunny with some low level (valley) cloud. Light and variable wind. Warmest temperatures at treeline and alpine elevations near zero.TUESDAY: Treeline and alpine temperatures just above zero. Wind becoming more westerly as the next pacific system approaches.

Avalanche Summary

Friday reports were of intentionally triggered small avalanches on small & low consequence "test slopes, larger (size 2.5 explosive triggered slides) and most interestingly (importantly) remotely triggered avalanches from 20m away. On Saturday a larger avalanche was triggered with explosives running on the November crust down 100 to 200 cm. This was a size 3.5 slide that ran nearly 800m and exceeded the path's historic runout distance.

Snowpack Summary

The snowpack remains near a tipping point. Cooler temperatures Friday and Saturday reduced the sensitivity slightly but forecast warming should bring us back closer to the balance point.Over 100 cm of snow fell within the past week.  The snow fell relatively warm with moderate winds, which formed storm slabs.  The snow also formed large cornices.  This storm snow sits on variable feathery surface hoar in the region.  Deeper in the snowpack, an unstable weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below treeline elevations.  Below, a rain crust that developed late-November with associated sugary facets are also being stressed. Snowpack test results show sudden fracture characters and high propagation potential for all of these buried layers, indicating that they can be triggered and could propagate into large, destructive avalanches. This has been the case, as shown in the Avalanche Summary.

Régions couvertes