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Avalanche Forecast

Archived

Feb 20th, 2022–Feb 21st, 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.

The weekend storm produced 4 to 8 cm of snow with wind out of the southwest, wind slabs may begin to form in unusual locations as wind switches to the north Sunday night into Monday. Watch for wind-loaded pockets, especially around ridge crest and in extreme terrain.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

SUNDAY NIGHT: Freezing level at valley bottom, no new snow expected, light northeast wind at most elevations with moderate gusts at ridge top.

MONDAY: A few clouds in the morning giving way to clear skies in the afternoon, no new snow expected, moderate northeast wind, daytime high temperature at 1500 m around -8 C.

TUESDAY: Clear skies, no new snow expected, moderate northeast wind, daytime high temperature at 1500 m around -10 C.

WEDNESDAY: Scattered cloud cover, no new snow expected, light variable wind, daytime high temperature at 1500 m warming slightly to -8 C.

Avalanche Summary

Thin wind slabs were reactive to ski cutting just below ridge crests Saturday afternoon.

On Thursday, a natural icefall triggered a size 2.5 avalanche on the slope below. This avalanche was on a northeast aspect at 2100 m.

On Wednesday, a size 1 natural cornice fall was observed on an east aspect at 2200 m. It was in extreme terrain and did not pull a slab on the slope below.

Snowpack Summary

The weekend storm produced 4 to 8 cm of snow with strong southwest wind that likely formed thin wind slabs in exposed terrain. 

The mid-February crust is down 10 to 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 to 100 cm. This layer was most reactive between 1700 m and 2000 m. While this layer now appears to be dormant in many parts of the region, it may be possible to trigger it with a large load or in shallow snow pack areas at upper treeline or lower alpine features on polar aspects.

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.