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

Regions

North 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, moderate northeast wind, treeline temperatures drop to -30 C.

FRIDAY: Sunny, light to moderate northeast wind, treeline temperatures around -18 C.

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

SUNDAY: Mix of sun and cloud, light wind, treeline temperatures around -15 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). These persistent slab avalanches likely failed on a facet and crust layer.

Several small to large (size 1-3) wind slab avalanches were reported earlier this week, some of which were triggered by solar radiation or cornice falls. Over the past week the persistent slab problem has produced fewer avalanches than in the first week of February, but is still showing signs of instability in snowpack tests and warrants careful and cautious assessment.

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. 60-100 cm of snow from February is settling over a layer of surface hoar. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features that are below treeline, however facets above a sun crust may be found on steep south facing features. Snowpack tests results continue to show the potential for propagation on this layer, like this MIN report from Clemina on Monday and this MIN report from the Gorge on Tuesday. The mid/lower snowpack is generally well settled and strong.

Terrain and Travel

  • Exercise caution on steep, unsupported slopes.
  • Carefully evaluate big/extreme terrain features before committing to them, it may not be full "go" time yet.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be careful as you transition into wind affected terrain.

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.