Avalanche Forecast
Issued: Apr 16th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.
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Avalanche Canada
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!
Summary
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
Watch for sensitive new storm and wind slabs at high elevations. In favoured snow holes, like upslope areas on the west side of the Purcells as much as 35 cm of snow is expected.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
The April Fools layer (buried on Apr 01) is especially reactive on solar tilted slopes, that is east through south and through to the west). It's a different problem on shady polar slopes where the weakness is more sugary facets. There are reports of surface hoar above the crust making it even more reactive and surprising. This layer is the culprit for the string of close calls and Saturdays fatal accident at Thunderwater Lake.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth.
Suspect terrain includes steep, shallow, and rocky terrain where the snowpack varies beween thin and thick.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 17th, 2023 4:00PM
