Avalanche Forecast
Issued: Mar 16th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Deep Persistent Slabs and Cornices.
rgoddard,
Avalanche Canada
Expect avalanche hazard to be at its highest during the warmest part of the day.
Avoid solar slopes in the afternoon especially if they contain overhead hazards.
Summary
Confidence
Avalanche Summary
Wednesday's avalanches were a mixed bag that included storm slabs, wind slabs, cornices, and deep persistent slabs. A few that caught people by surprise were triggered accidentally by riders and vehicles, some of which were set off remotely. They were found on all aspects and the wind and storm slabs were triggered up to 50 cm deep on the March 11th layer that the most recent storm snow covered up.
Explosives were used to trigger the cornice avalanches, most of which were size two. The load that these falling cornices placed on the snowpack below did not trigger buried weak layers. However, a natural size 3.5 avalanche was triggered and it ran on the deep persistent layer, buried 100 cm, from November. This is a good reminder that solar input can "wake up" these deeper layers.
Snowpack Summary
A storm slab, 40 to 60 cm, overlies a variety of surfaces, which include surface hoar, 3 to 10 mm, on shady slopes at all elevations, wind-affected surfaces at treeline and above, and sun crust on sunny aspects. Moderate to strong southerly winds that accompanied this snow may have created wind slabs at higher elevations. Solar aspects and lower elevations will be affected by day time warmer and nighttime freezing. Expect a crust in the morning and moist snow in the afternoon.
The mid-snowpack is generally strong but the lower snowpack is a different story.
The November facets are still prominent at the base of the snowpack. They are showing signs of improving but this layer remains a significant concern in rocky, shallow, or thin to thick snowpack areas at treeline and above.
Weather Summary
Thursday Night
Clear, no accumulation, winds southeast 10 to 15 km/h, treeline temperatures -5 °C with freezing levels dipping to 1200 m.
Friday
Sunny, no accumulation, winds southeast 10 to 15 km/h, treeline temperatures -5 to 0 °C with freezing levels getting up to 1800 m.
Saturday
Mostly sunny, no accumulation, winds southeast 10 to 15 km/h, treeline temperatures -5 to 0 °C with freezing levels getting up to 1800 m.
Sunday
A mix of sun and cloud, no accumulation, winds southerly 10 to 15 km/h, freezing levels to 1900 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
- Don't let the desire for deep powder pull you into high consequence terrain.
- A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- Be carefull around freshly wind loaded features.
Problems
Storm Slabs
Forecasted solar input could promote slab reactivity. A storm from earlier in the week brought us 40 to 60 cm of snow. This storm slab problem may remain reactive for longer than expected due to the uncertainty of how this new snow is binding with old surfaces.
Moderate to strong southerly winds that were associated with this past storm will have loaded lee features creating pockets of increased reactivity.
Aspects: All aspects.
Elevations: All elevations.
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, but large triggers such as cornice failures or smaller avalanches in motion have the potential to produce very large avalanches with surprisingly wide propagation. Suspect terrain for human triggering includes steep, shallow, and rocky terrain where the snowpack transitions from thin to thick.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Cornices
Solar input could weaken cornices that have been building all season.
If the release, cornices could trigger weaker layers buried in the snowpack.
Aspects: East, South East, South, South West, West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 17th, 2023 4:00PM
