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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.
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

South Rockies.

Wind slabs continue to be a concern at higher elevations. 

Approach steep open slopes at treeline and below with caution. A buried surface hoar layer may become may be reactive to human triggers. Watch for signs of instability as you travel.

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: Mostly cloudy. Moderate westerly winds. Freezing level at valley bottom. Isolated flurries possible. 

FRIDAY: Cloudy with flurries deliver less than 5 cm by the end of the day. Strong westerly winds. Freezing level rises to around 1000 m. Alpine high of -5.

SATURDAY: Mostly clear with moderate westerly winds. Freezing levels rise around 1500 m, with alpine highs of -3. Moderate westerly winds. 

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

Avalanche Summary

Loose dry activity has been noted over the last few days, to size 1 and 1.5. Natural slab activity was last observed on Monday to size 2. Small storm slabs were also triggered by ski cutting and explosives on Monday.

Shooting cracks and whumpfing have been reported by industry operators and in several MIN reports in specific areas. While the surface hoar is only found in specific areas, it is sensitive to human triggers.

Snowpack Summary

At lower elevations 20-40 cm of storm snow sits over a melt freeze crust observed to 2000 m. 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 into pockets of wind slab by strong westerly winds. A thin melt freeze crust extends into the alpine on solar aspects. This crust may sit on the surface in exposed terrain, or below wind deposited snow in sheltered areas increasing reactivity.

The early December crust/facet persistent weak layer is now 100-200 cm deep. This layer produced numerous very 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.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be alert to conditions that change with elevation and wind exposure.

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.