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Avalanche Forecast

Archived

Feb 11th, 2021–Feb 12th, 2021

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.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Avalanche activity has slowed down, but there is a lingering potential to trigger large avalanches on buried weak layers. Read about managing these conditions in this forecaster blog. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Brrrrrr! Cold and dry conditions persist under arctic air...

THURSDAY NIGHT: Clear skies, light northeast wind, treeline temperatures drop to -25 C.

FRIDAY: Sunny, light to moderate northeast wind, treeline temperatures around -15 C.

SATURDAY: Sunny with a few clouds, light to moderate east wind, treeline temperatures around -15 C.

SUNDAY: Mix of sun and cloud, light wind, treeline temperatures around -12 C.

Avalanche Summary

Avalanche activity has started to slow down over the past few days with reports from Wednesday primarily consisting of small isolated wind slabs and dry loose avalanches (size 1). However, there were two notable human triggered avalanche just outside Glacier National Park on Wednesday where a size 2.5 and a size 3 avalanche were triggered on south and west facing alpine slopes (MIN report). This is a reminder of the lingering possibility of large persistent slab avalanches. There were numerous reports of persistent slab avalanches last weekend and earlier this week including some in lower elevation cutblocks in the southern Selkirks (here and here), a wind slab on a southeast aspect that stepped down to a deeper layer to produce a size 3 avalanche on London Ridge, and a size 1.5 skier triggered slab near Revelstoke (MIN report).

Snowpack Summary

The upper snowpack is becoming soft and faceted with the cold temperatures, while recent wind has left some wind slabs in lee features. 60-120 cm of snow from February is settling over a weak layer of surface hoar that has shown reactivity at treeline or in "treeline-like" features below treeline. On steep south facing terrain this layer may consist of facets on a sun crust. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. This layer will be slow to gain strength and requires careful terrain selection. The mid/lower snowpack is generally strong and settled in most areas.

Terrain and Travel

  • Exercise caution on steep, unsupported slopes.
  • Carefully evaluate big/extreme terrain features before committing to them, it's not full "go" time yet.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Carefully evaluate steep lines for wind slabs.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.