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Avalanche Forecast

Archived

Apr 16th, 2023–Apr 17th, 2023

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

Regions

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

Some localized snow-holes may see more than 30 cm of fresh snow on Monday; if that's the case where you're riding bump the Danger Rating to HIGH.

At upper elevations, especially on east, south, or west aspects where the previous snow sits on a crust, avalanches 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.

Also on Saturday, were a pair of size 2.5 Loose Wet and Persistent slab avalanche in Glacier National Park.

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.

It's still winter out there; as the snowpack slowly transitions to spring, riders need to manage a wide range of avalanche concerns that vary by elevation and aspect.

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

Sunday Night

Snow; accumulations around 5 to 30 cm; the most snow is forecast for upslope areas (e.g. west side of the Purcells, west side of the Selkirks south of Revelstoke) and the lowest amounts in the north. Freezing level around 1000 m. Wind moderate to strong from southwest.

Monday

As the storm winds down most of the day should see a mix of sun and cloud. Flurries with only an trace more snow. Freezing level climbs to around 1700 m and alpine temperatures around -5 C. Light, gusting to moderate, southwest winds.

Tuesday

Cloudy with sunny periods and light snow. A trace to maybe 10 cm in localized snow holes. Freezing level climbs to around 1600 m and alpine temperatures around - 5 C. Light southwest winds.

Wednesday

Cloudy with sunny periods and isolated flurries. Only a trace of new snow. Freezing level climbs to around 1700 m. Alpine temperatures zero to -5 C. Light wind.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be alert to conditions that change with elevation and sun exposure.
  • 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.

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.