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Avalanche Forecast

Archived

Feb 25th, 2020–Feb 26th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

Wind slabs have been triggerable by riders in the past few days. As snowfall continues to accumulate, slabs may become surprisingly touchy where they rest on surface hoar.

Confidence

High -

Weather Forecast

TUESDAY NIGHT: Partly cloudy with isolated flurries, accumulation 1 to 3 cm, moderate west wind, alpine temperature -7 C.

WEDNESDAY: Morning snowfall and afternoon clearing, accumulation 2 to 5 cm, moderate west wind, alpine temperature -8 C, freezing level rising to 1400 m.

THURSDAY: Partly cloudy with isolated flurries, accumulation 1 to 3 cm, light to moderate west wind, alpine temperature -5 C, freezing level rising to 1500 m.

FRIDAY: Partly cloudy with isolated flurries, accumulation 1 to 3 cm, light southwest wind, alpine temperature -4 C, freezing level 1600 m.

Avalanche Summary

A few small (size 1 to 1.5) wind and storm slab avalanches were triggered by skiers and naturally on Monday. They generally occurred on north to east aspects but one occurred on a southwest aspect. They were 20 to 30 cm thick and occurred at alpine elevations.

Snowpack Summary

Around 10 to 30 cm of recent snow covers a widespread layer of surface hoar (size 5 to 15 mm) that was found at all elevations and on all aspects. On southeast through southwest facing slopes, this surface hoar likely grew on a thin melt-freeze crust, which is a nasty combination. The recent snow has been blown around by variable wind, forming wind slabs at higher elevations, particularly near ridges.

The middle of the snowpack is strong. The base of the snowpack contains basal facets, which have been responsible for occasional and hard-to-predict Deep Persistent Slab avalanches in shallow rocky start zones.

Terrain and Travel

  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.