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Avalanche Forecast

Archived

Jan 23rd, 2022–Jan 24th, 2022

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 unlikely, human triggered possible.
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.

Regions

Lizard-Flathead.

The danger ratings don't tell the whole story. Uncertainty regarding the Deep Persistent Slab problem would have me avoiding any large or committing features. 

Confidence

Moderate - We have a good understanding of the snowpack structure and confidence in the weather forecast Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Sunday Night: Mostly cloudy. Possible trace of snow expected. Light southwest wind trending to moderate northwest at higher elevations. Freezing level dropping to near valley bottom. 

Monday: Mostly cloudy, possible clearing in the afternoon. ~3 cm of snow expected. Light northeast wind with periods of strong at higher elevations. Freezing levels rise to 1000 m, alpine low around -6 C.

Tuesday: A mix of sun and cloud. No new snow expected. Moderate southwest wind trending to strong northwest at higher elevations. Freezing levels drop to valley bottom overnight, rise back to 1000 m by the afternoon.

Wednesday: Partly cloudy. Possible trace of snow expected. Moderate southwest wind, trending to extreme northwest at higher elevations. Freezing levels drop to valley bottom overnight, rise back to 1000 m by the afternoon. 

Avalanche Summary

On Saturday, avalanche control with explosives produced a couple of small windslab avalanches around treeline. Also, neighbouring Waterton National Park reported a few natural windslab avalanches to size 2 on solar aspects in the alpine. 

On Friday, several wind slabs and storm slabs up to size 2 were reported. A natural cornice fall also occurred pulling a size 1.5-2 storm slab in the fans on the slope.  

Snowpack Summary

Surface hoar up to 10 mm has been reported around Fernie. At this time it is unknown if this surface hoar growth is more widespread. Expect to find patchy sun crust on steep, solar aspects below treeline. The previously forecasted above freezing layer seemed to be less prominent and at a higher elevation than originally expected, but this sun crust could also exist in the high alpine. 

Up to 15 cm of new storm snow fell Thursday with fairly light winds. Moderate to strong winds from the southwest on Friday stripped some windward slopes, and formed variable wind slabs. These slabs are up to 60 cm thick in lee features.

Around 2200 m and below, these windslabs overlie a crust buried on January 18th, which caps a dense 15 to 30 cm of settled snow. The crust varies with aspect and elevation from thin (2 cm thick) in the alpine to (4 cm) thick below treeline. Below this, the midpack is well consolidated above the early December crust/ facet interface.  

The most notable layer of concern in the snowpack is a widespread crust that was formed in early December and is now down 100-270 cm. With warming last week this deep persistent slab problem woke up and produced several very large avalanches. Daytime warming, solar radiation, smaller avalanches, and cornice fall could continue to play a role in triggering deep persistent slabs. 

Terrain and Travel

  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid terrain traps where the consequence of any avalanche could be serious.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.