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

Regions

Lizard-Flathead.

Recent reverse loading from northeast winds have formed wind slabs in unusual places. There is uncertainty about how quickly slabs will bond to old surfaces like melt-freeze crusts and hard wind-pressed snow. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

TUESDAY NIGHT: Mostly clear, winds light to moderate from the northeast. Alpine low -27.

WEDNESDAY: Mostly sunny with increasing afternoon cloud. Light northwest to southwest winds. Alpine high of -16. 

THURSDAY: Light flurries possible overnight Wed/Thurs. Partly cloudy, light north wind, alpine high of -10.

FRIDAY: Mix of sun and cloud. Light southwest wind and alpine highs of -10.

Avalanche Summary

On Monday a skier accidentally triggered a wind slab on a reverse loaded feature in the Lizard Range (MIN here). There were other reports of small natural and skier-controlled wind slabs in the region on Monday as well. On Saturday there was a machine triggered avalanche on an old buried surface hoar layer in an open gully feature in the Rolling Hills area.

Snowpack Summary

The 5-15 cm of most recent snow has been redistributed by moderate to strong northeast winds and has formed wind slabs in unusual places. In south-facing terrain, new snow sits on top of melt-freeze crusts, and in open terrain recent snow sits over old firm wind-affected surfaces. 

A buried surface hoar layer may be found 30-50 cm deep on sheltered, north-facing treeline-type features. This layer has become significantly less reactive and harder to find, but it can still catch riders off guard in isolated areas. Check out this recent MIN from the Rolling Hills area for an example.

The lower snowpack is well consolidated, with a crust/facet layer found near the bottom of the snowpack. It is currently considered dormant, but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried 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.