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Avalanche Forecast

Archived

Feb 6th, 2022–Feb 7th, 2022

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

Regions

South Rockies.

Ongoing periods of strong wind continue to develop reactive wind slabs in exposed terrain and two buried weak layers remain a concern for persistent slab avalanches. Give the snowpack time to recover from the recent warming and continue to use a conservative mindset.

Confidence

Low - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to the limited number of field observations.

Weather Forecast

Freezing levels may stay elevated overnight and Monday morning but there is still a lot of uncertainty regarding the intensity and extent of any lingering warming. 

Sunday Night: Mainly clear, moderate to strong SW wind, freezing levels 1500-2000 m with a temperature inversion.

Monday: Increasing cloud cover in the afternoon with a chance of flurries, moderate to strong SW wind, afternoon freezing levels around 1600 m. 

Tuesday: Mainly sunny, light to moderate SW wind, freezing levels reaching around 1600 m.

Wednesday: Mainly sunny, light to moderate W wind, freezing levels climbing to around 2000 m.

Avalanche Summary

This MIN report from Saturday describes a natural size 1.5 slab avalanche on a south aspect as well as shooting cracks and whumpfing while travelling. It also suggests the surface snow was getting warm and consolidating into a slab. 

On Friday, four natural size 1.5 wind slabs were reported by the field team in this MIN post failing down 30 cm on a crust in cross-loaded terrain. 

Snowpack Summary

20-40 cm of rapidly settling snow now typically overlies the January 30 interface which consists of a melt-freeze crust to around 2000 m and on solar aspects extending into the alpine, surface hoar in wind-sheltered areas at and below treeline, and small facets in some areas. With the recent warming, the surface snow has settled into a cohesive slab over the weak layer and a new surface crust will likely form as temperatures drop.

Periods of strong wind over the weekend, mainly from the southwest through northwest, have formed reactive wind slabs in exposed terrain at higher elevations. Ongoing wind on Monday will likely continue to develop reactive wind slabs where there is still loose snow available for transport.

The early December crust/facet persistent weak layer is now 100-200 cm deep. This layer produced numerous very large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season. 

Terrain and Travel

  • 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.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Extra caution is needed around cornices under the current conditions.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.