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Avalanche Forecast

Archived

Apr 20th, 2023–Apr 21st, 2023

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

Regions

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, Retallack, Valhalla, Whatshan.

It's a challenge to manage different avalanche concerns that vary by elevation and aspect. Observe local conditions and use that information to help select terrain and travel techniques. Match terrain to conditions!

The April Fools Day crust, up to 100 cm below the surface remains a concern, especially on east, south, or west facing slopes at treeline and higher elevations.

Confidence

Moderate

Avalanche Summary

On Wednesday a size 3 Glide Slab was reported on a south facing rock slab releasing near treeline. Explosive cornice control work mostly resulted in large chunks dropping but out of 10 events only 2 pulled size 2 slabs from the slopes below (in the Purcells).

A number of persistent slab avalanches were reported on Tuesday, up to size 2. They were a combination of explosive and skier triggered, and all appear to have failed on lingering and problematic April Fools Day surface hoar/crust combination. All reported avalanches occurred in the western Purcells.

In the Selkirks the avalanche activity appears to be slowing. However, many natural and human-triggered avalanches were reported last week. Many of these slid on the same April Fools Day crust, including a fatal avalanche in the western Purcells and a close call near Revelstoke.

Snowpack Summary

Dry, powder snow remains at higher elevations on north-facing terrain. While multiple melt-freeze crusts or moist snow are found in the snowpack on steep solar slopes and at lower elevations.

A layer of surface hoar from March 31 persists down roughly 50 to 100 cm appears to be variable in its distribution. The surface hoar may be sitting above a crust on all but true north-facing slopes. Despite a decrease in avalanche activity on this layer, avalanche professionals continue to closely monitor it. Additionally there are similar crusts dating from April 16 and April 7 higher up in the snowpack with similar characteristics and concerns.

The mid-snowpack is strong. However, the November depth hoar remains at the base of the snowpack and remains a concern in rocky, shallow, variable depth snowpack areas at treeline and above.

Weather Summary

Thursday Overnight

Cloudy with clear periods and flurries; only a trace of precipitation. Light, with moderate gusts, southwest winds. Treeline temperatures around -5 to -10 C. Freezing level at valley bottom.

Friday

A mix of sun and cloud with just a trace of precipitation, maybe as much as 5 cm at favoured high elevation upslope locations. Light southwest ridgetop winds. Treeline temperatures around -5 C. Freezing level around 1800 to 2000 m.

Saturday

Cloudy with sunny periods and isolated flurries.. Just a trace of new snow. Light southwest ridgetop winds. Treeline temperatures around -5 C. Freezing level around 1900 m.

Sunday

Mostly cloudy with flurries and just a trace of new snow except around 5 cm on favoured upslope areas. Moderate southerly winds. Treeline temperatures around zero and freezing level around 2100 to 2300 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • Be alert to conditions that change with elevation and sun exposure.
  • Closely monitor how the new snow is bonding to the crust.
  • Be carefull around freshly wind loaded features.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.