Avalanche Forecast
Issued: Jan 18th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Deep Persistent Slabs.
swerner,
Avalanche Canada
A reactive weak layer is producing large human-triggered slab avalanches. The problem is especially prevalent at mid-elevations. With a complex snowpack, terrain choices and good group management techniques are key. Regroup in safe locations, space out, and avoid rocky, thin-to-thick snowpack areas.
Summary
Confidence
Moderate
Avalanche Summary
On Tuesday, improved weather allowed for better visibility noting the widespread natural avalanche activity that occurred last weekend. Most of these avalanches reportedly failed on the surface hoar interface buried early January. Explosive control results included large deep persistent slab avalanches up to size 3 and storm slabs to size 2. Human triggering and remote triggering remain possible, especially 1700-2100 m being the critical elevation band and east-to-northeast aspects on the buried surface hoar layer.
Snowpack Summary
Upper elevations have received 20-35 cm of new snow over the past week. It overlies a mix of wind-affected and sheltered low-density storm snow above about 1700 m and a rain crust at lower elevations.
At higher elevations, 40 to 60 cm of snow now sits on a layer of surface hoar that was primarily preserved in sheltered terrain at treeline. It has been identified as the failure plane in many recent avalanches in the region.
A facet/crust layer is down 40-90 cm (and 2-10 cm thick at TL elevation). Below this, the mid-pack is settled and consolidated.
A concerning and weak layer of facets and crust 20-50 cm thick make up the basal snowpack.
Weather Summary
Wednesday Night:New snow 5-10 cm overnight. Steady ridgetop winds from the southwest. Alpine temperatures near -7 C and freezing levels valley bottom.
Thursday: Mainly cloudy with sunny breaks and isolated flurries. Alpine temperatures reach a high of -7 C. Ridgetop wind light from the northwest. Freezing level rises to 1000 metres.
FridayA mix of sun and cloud. Alpine temperatures reach a high of -4 C. Ridge wind light from the northwest. Freezing level near 1000 m.
SaturdaySunny. Alpine temperatures reach a high of -5 C. Ridge wind mostly light with moderate to strong gusts from the northwest. Freezing level rises to 800 metres.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
- Uncertainty is best managed through conservative terrain choices at this time.
Problems
Persistent Slabs
Recent snowfall has been activating a persistent weak layer 50-60 cm deep. In many cases, this interface has been even more reactive than the new snow interface above it. Additional flurries and ridgetop wind will keep this problem near its tipping point in the coming days.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Weak, faceted grains make up the basal snowpack. Where supportive to riders, a melt-freeze crust may be providing a bridging effect, making it more difficult to trigger deeper layers. Be especially suspicious of shallow, rocky, or cross-loaded areas with variable snow depths.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 19th, 2023 4:00PM
