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Avalanche Forecast

Archived

Feb 13th, 2021–Feb 14th, 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, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Watch for wind slabs in unusual places as winds shift again, this time to the south. Uncertainty about triggering large avalanches warrants careful terrain selection. Read about managing these conditions in this forecaster blog. 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SATURDAY NIGHT: Mostly cloudy, light southeast wind, alpine temperatures around -17 C.

SUNDAY: Cloudy with sunny breaks, light south wind, alpine temperatures around -16 C.

MONDAY: Mix of sun and cloud, light variable wind, alpine temperatures around -12 C. 

TUESDAY: Cloudy, light west winds with moderate gusts at ridgetop, isolated flurries with trace accumulations, alpine temperatures around -13 C.

Avalanche Summary

Operators on Friday reported small to large (size 1-2) wind slab avalanches near treeline and above as a result of moderate east winds. This MIN report from neighboring Glacier National Park offers a helpful visual of this avalanche activity. There continue to be reports of small dry loose avalanches. 

Observations of avalanches on the late January persistent weak layer continue to trickle in. This MIN report from Friday shows that the surface hoar remains alive and well on lower elevation cutblock features. Last week, a wind slab on a southeast aspect was thought to step-down to the late January crust/facet interface to produce a size 3 avalanche on London Ridge, and there was a size 1.5 skier triggered slab near Revelstoke (MIN report).

Snowpack Summary

Winds are forecast to shift to a new direction overnight (southeast) and again tomorrow (south) and may form fresh wind slabs in lee features at upper elevations. Previous winds blew from the east/northeast with enough gusto to move snow around and build reactive wind slabs. Watch for these wind slabs in unusual places as tricky cross-loading and reverse-loading continues. 

While wind may be forming slabs in lee features, the upper snowpack is becoming soft and faceted with the cold temperatures. 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, like cutblocks, below treeline. On steep south-facing terrain, this layer may consist of facets on a sun crust. This persistent weak 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

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Approach lee and cross-loaded slopes with caution.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Extra caution is needed around cornices under the current conditions.

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.

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.