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Avalanche Forecast

Archived

Feb 3rd, 2022–Feb 4th, 2022

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

Regions

Lizard-Flathead.

A buried surface hoar layer may become more reactive as storm snow accumulates. Approach steep open slopes at treeline and below with caution. 

Watch for signs of instability as you travel. Consider conservative terrain choices as a way to manage uncertainty.

Confidence

Moderate - We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering. Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

Light snowfall is forecast for Friday. Temperatures rise and skies clear for the weekend.

THURSDAY NIGHT: Cloudy with moderate westerly winds. Freezing level at valley bottom. Scattered flurries.

FRIDAY: Cloudy with 5 -15 cm of low density snow. Strong westerly winds. Freezing level 1000 m, alpine high of -5. 

SATURDAY: Mostly clear with cloudy periods, a chance of flurries. Moderate westerly winds. Freezing levels around 1500 m, alpine high of -3. 

SUNDAY: Mostly clear with moderate westerly winds. Freezing levels rise to 2000 m, alpine high of 0.

Avalanche Summary

Recent avalanche activity has been limited to small loose dry avalanches out of steep terrain features. 

Shooting cracks and whumpfing have been reported by industry operators and in several MIN reports. This indicates the buried surface hoar layer is sensitive to human triggers.

On Monday, a size 2.5 natural persistent slab avalanche was reported to have occurred on a path that had previously avalanched where storm snow reloaded bed the surface.

Snowpack Summary

At lower elevations up to 40 cm of storm snow sits over a melt freeze crust. In sheltered terrain a layer of large surface hoar crystals may sit immediately above the crust, sensitive to human triggers.

At higher elevations the storm snow has been redistributed by moderate to strong westerly winds. A thin melt freeze crust extends into the alpine on solar aspects. This crust may sit on the surface or below wind deposited snow. 

The widespread January 18 rain crust is now around 40-50 cm deep with weak faceted snow above, however it has not produced recent avalanche activity.

The early December crust/facet persistent weak layer is now 100-200 cm deep. This layer produced numerous large avalanches in January, and is now considered dormant. We will continue to track this layer of concern and expect it will wake up again with major warming or a large storm event. This recent forecaster blog goes into more details on the layer.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.

Problems

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.

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.