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Avalanche Forecast

Archived

Mar 15th, 2020–Mar 16th, 2020

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

Regions

South Columbia.

Expect an upward swing in temperatures as the freezing level rises on Monday. This shift in temperature may result in an increased likelihood of triggering persistent slab avalanches. Be especially cautious underneath steep sun exposed slopes and around rock outcrops.

Confidence

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

Weather Forecast

SUNDAY NIGHT: Mainly clear, light northeast wind, alpine temperature -7 C.

MONDAY: Clear skies, light northwest wind, alpine temperature -3 C, freezing level 1700 m.

TUESDAY: Mix of sun and cloud, light northwest wind, alpine temperature -3 C, freezing level 1700 m.

WEDNESDAY: Mix of sun and cloud, light northeast wind, alpine temperature -4 C, freezing level 1500 m.

Avalanche Summary

Recent reports show several natural wind slab avalanches ranging in size from 1.5 to 2.5 running in the alpine on east, southeast and north aspects at treeline and in the alpine. There was also a report of a natural size 2 persistent slab avalanche in the far south of the region running on the late February surface hoar layer. This was on a southwest aspect at 1700 m and was 50 cm deep. This layer continues to surprise people with remote-triggered activity, wide propagation, and a false sense of stability from unreactive ski cuts or from multiple people moving through the terrain before an avalanche releases (see this Instagram report as a good example).

Snowpack Summary

Moderate northeast wind has redistributed the snow and formed wind slabs in exposed terrain. The recent snow may sit on a surface hoar layer and a sun crust on steep solar aspects.

A widespread weak layer of surface hoar is buried 60-120 cm deep. On solar aspects, this layer may sit over a crust. There is a low likelihood of triggering an avalanche on this layer, but the consequences of doing so would be high. Read more about surface hoar on our forecaster blog.

Terrain and Travel

  • 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.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Minimize exposure to steep, sun exposed slopes, especially when the solar radiation is strong.

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.