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Avalanche Forecast

Archived

Feb 22nd, 2022–Feb 23rd, 2022

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

Sea To Sky.

Recently formed wind slabs are expected to remain reactive to human-triggering in exposed high elevation terrain on Wednesday. 

Confidence

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

Weather Forecast

High pressure remains the dominant feature for the rest of the week. However, a disturbance is expected to move through the region late Wednesday bringing increased cloud cover, shifting winds, and a chance of flurries. 

Tuesday Night: Clear, light to moderate N wind, treeline low around -16 °C.

Wednesday: Mainly sunny with increasing cloud in the late afternoon, moderate to strong NW wind, treeline high around -8 °C.

Thursday: Mainly sunny, light N wind, treeline high around -3 °C.

Friday: Sunny, light SW wind, treeline high around -2 °C.

Avalanche Summary

On Monday, a natural size 2.5 cornice release was observed on a north aspect at 1900 m which pulled a small slab on the slope below. One natural size 1 wind slab was observed and skiers triggered several size 1 wind slabs. One of these was on a north aspect while the rest were on southeast through southwest aspects. 

On Sunday, natural size 1 wind slabs were being observed as well as some isolated natural loose activity. A natural size 2 cornice was also reported which did not trigger a slab. 

On Thursday, a natural icefall triggered a size 2.5 slab avalanche on the slope below. This avalanche was on a northeast aspect at 2100 m. Details were limited but we expect this may have been a persistent slab avalanche. 

Snowpack Summary

The weekend storm produced 5-10 cm of snow with strong southwest wind that likely formed thin wind slabs in exposed terrain. On Monday, the wind switched to a northeast direction causing reverse loading and thin wind slabs may now exist on all aspects in exposed terrain. 

The mid-February crust is down 10-30 cm. This melt-freeze crust is reported to exist on all aspects and elevations, except for some of the highest elevation polar aspects. Facets have been observed above the crust on polar aspects.

The late-January crust/facet/surface hoar interface is buried down 40-100 cm. This layer was most reactive between 1700 m and 2000 m. While this layer now appears to be dormant through most of the region, it may still be possible to trigger it at upper treeline or lower alpine features on polar aspects with a large load like a cornice or in shallow snowpack areas.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Closely monitor how the new snow is bonding to the crust.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.