Avalanche Forecast
Issued: Apr 10th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
jsmith,
Avalanche Canada
Storm slabs will likely be reactive to human triggers; especially in wind-affected terrain and/or where the recently formed slabs are sitting on weak facets.
Choose conservative terrain and watch for clues of instability.
Summary
Confidence
Avalanche Summary
A very large (size 3) explosive triggered a persistent slab avalanche on a west aspect in the alpine was reported on Monday.
On Sunday, explosive triggered persistent slabs up to size 3 were reported on primarily northerly aspects in the alpine. Additionally, a size 2 wind slab (40 cm deep) was triggered by a helicopter landing on a ridge. The avalanche occurred on a north aspect at treeline and sympathetically triggered three more avalanches below the ridge.
Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.
Snowpack Summary
30-60 cm of recent snow fell dry above 1500 m and as rain below 700 m. At upper elevation, the new snow continues to be redistributed by southwest winds into wind slabs on north-to-east-facing slopes. The recent snow sits over wind-affected surfaces, weak faceted crystals or a crust on south-facing slopes.
A weak layer buried at the end of March sits 50-80 cm deep in most areas (potentially over 1m deep in immediate coastal terrain). It includes facets and surface hoar in shaded areas, and a melt-freeze crust elsewhere.
The mid and lower snowpack are considered generally strong and well-bonded. In far northern reaches of the region, basal facets may exist which are currently considered inactive. This layer may become active with abrupt changes to the snowpack, such as rapid loading (heavy snowfall or rain) or prolonged warming.
Weather Summary
Monday night
Snow; 10-20 cm / 20 km/h south ridgetop wind / Temperature at treeline around -7 C / Freezing level valley bottom
Tuesday
Mostly cloudy with isolated flurries; 0-3 cm / 10 km/h west ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m
Wednesday
Mix of sun and cloud / 10 km/h west ridgetop wind / Temperature at treeline around -6 C / Freezing level 900 m
Thursday
Cloudy with isolated flurries; 0-5 cm / 20 km/h south ridgetop wind / Temperature at treeline around -5 C / Freezing level 900 m
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Avoid freshly wind loaded terrain features.
Problems
Storm Slabs
Storm slabs will likely be reactive to human triggers; especially in wind-affected terrain and/or where the recently formed slabs are sitting on weak facets.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Buried layers from late March reached a tipping point and recently became reactive.
The primary concern is a layer of facets and surface hoar buried 50-80 cm on shaded slopes. On other slopes, this layer is a crust with facets above. Avoid steep open slopes capable of producing large avalanches, storm snow is adding a significant load to the snowpack.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 11th, 2023 4:00PM
