Avalanche Forecast
Issued: Jan 14th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
A bit of new snow and wind will keep storm slabs fresh Friday. They will be especially reactive in wind loaded lees and where they sit over a persistent weak layer.
Where overnight precip falls as rain in the south, conditions will be crusty and avalanche danger a step lower.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Thursday night: Rain/snow, 5-10 mm/cm, strong to extreme southwest ridgetop wind, freezing level 1300 m in the north, 2500 m in the south.
Friday: Mix of sun and cloud, moderate to strong westerly ridgetop wind, freezing level 1300 m. Â
Saturday: Mix of sun and cloud, light southwest wind, freezing level 800 m.
Sunday: Flurries, strong southwest wind, freezing level 1300 m.
Avalanche Summary
A widespread natural avalanche cycle size 2-3 occurred throughout the region on Wednesday. Avalanche character was predominantly storm slab in the snowy north of the region and wet loose or glide slab in the rainy south. Northwest of Pemberton, several stepped down to buried weak layers resulting in very large (size 3-4) persistent slab avalanches.
Snowpack Summary
40-60 mm of recent precipitation fell as snow in the north and rain in the south. At latitudes and elevations that received snow, strong winds have formed reactive storm slabs. These slabs may be extra sensitive where they overlie surface hoar in sheltered terrain or a crust on solar aspects. Lower elevations and latitudes will see a firm surface crust as temperatures drop Friday.
A melt-freeze crust from early December is found around 100 to 200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the North (e.g., Duffey Lake, Hurley) and large avalanches have failed on this interface recently. This interface doesn’t seem to be a concern in the South (Coquihalla) and little information is known for the North Cascades or far South in Manning Park.
Terrain and Travel
- Make conservative terrain choices and avoid overhead hazard.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Problems
Storm Slabs
Watch for freshly wind loaded pockets of storm slab on leeward slopes in the alpine. Cornices have grown large and fragile. They deserve respect and a wide berth from below and above.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple of problematic layers may be found around 100 to 200 cm deep. The layers are primarily in the north of the region (e.g. Duffey, Hurley) and include weak layers of surface hoar and faceted grains above a hard melt-freeze crust. The likelihood of triggering a persistent slab has reduced, but the consequence of doing so remains high.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 15th, 2021 4:00PM
