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Avalanche Forecast

Archived

Apr 15th, 2023–Apr 16th, 2023

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

Regions

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

Forecast Update April 16, 0800 PDT: Please see Avalanche Summary under the Details Tab

At upper elevations, especially on east, south, or west aspects where the dry snow sits on a crust, storm slabs have been propagating widely, are surprisingly deep, and could be triggered by warmth, cornices, or riders. Reports of whumpfing from the west side of the Purcells are noteworthy and worrisome!

Confidence

Moderate

Avalanche Summary

A fatal avalanche occurred on April 15 in the Thunderwater Lake riding area. The size 3 (very large) avalanche was triggered near a rocky area. Two riders were caught, one was buried approximately 2 meters deep and did not survive. Any additional information we have available can be found in this MIN.

Friday's reports show the weak layers, up to 80 cm below the surface, were reactive to explosives, skiers, and naturally. Sizes were between 2 and 3.5. Additionally, there are stories about whumpfing around moraines. Explosives targetting the deep persistent layer at the bottom of the snowpack released several size 3.5 avalanches up to 200 cm thick.

Thursday's avalanche reports spoke to the continued storm slab or persistent slab avalanche problem (previous dry snow above crusts or facets from April 7 or March 31) with several avalanches to size 3.5, many seemed to release with daytime warming. Some were cornice triggered.

A serious avalanche incident occurred in the backcountry just east of Revelstoke on Wednesday. Details are available here. This is representative of the "recent storm snow above a crust" problem.

Looking forward, the need for backcountry travelers to manage a wide range of avalanche concerns that vary by elevation and aspect continues.

Snowpack Summary

At the surface crusts have formed on solar aspects and surface hoar is growing on shady aspects. At high elevations (where winter remains and the snow is dry) around 30-60 cm of previous storm snow is settling and remains dry (at least on shady terrain).

Recent snow overlies two lingering weak layers: a widespread melt-freeze crust buried April 7 and a layer of faceted snow or surface hoar buried April 1. Whumpfs and numerous recent avalanches, some with wide propagation, are attributed to these lingering problem layers.

The mid-snowpack is strong. However, 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

Saturday Night

Cloudy with clear periods and isolated flurries. Only a trace of new snow. Freezing level falling to around 1200 m. Light to moderate south wind.

Sunday

Cloudy with sunny periods and showers during the day. New snow around 2 - 5 cm but possibly as much as 10 cm south of Revelstoke. Freezing level around 2100 m. Light to moderate southwest wind. Treeline temperatures around 0 C. Snow picks up after the sun sets with up to 15 or 20 cm of snow (favoured areas are south of Revelstoke and the west side of the Purcell Mountains) by Monday morning.

Monday

Cloudy with sunny periods and an additional 2 to 5 cm accumulating. Again, highest accumulations in the south. Freezing level around 1700 m and treeline temperatures around -5 to -10 C. Light to moderate westerly winds.

Tuesday:

A mix of sun and cloud with flurries. A trace to 5 cm of new snow. Freezing level around 1700 m and treeline temperatures around -3 to - 8 C. Light southwest winds.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
  • 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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.