Avalanche Forecast
Issued: Feb 17th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
New snow and wind will build reactive storm slabs. They may be more sensitive on leeward slopes in the alpine and treeline. Uncertainty remains around a buried weak layer in the upper snowpack.
Make conservative terrain choices, particularly with warm temperatures and new load.
Summary
Confidence
Weather Forecast
The North and South Columbia will receive the bulk of its precipitation on Saturday as the front slides south. Winds will be 30-40km/h with gusts to 50.
Thursday Overnight: Snow 5-10 cm. Alpine temperatures -10 and freezing levels valley bottom. Moderate westerly winds.
Friday: Snow amounts 5-10 cm. Freezing level rising to 1800 m. Alpine temperature near -5 with strong westerly winds.
Saturday: Snow 15-20 cm. Freezing level rising to 1000 m and alpine temperatures near -5. Strong West wind.
Sunday: Flurries. Freezing level valley bottom and alpine temperature near -10. Moderate Southwest wind.
Avalanche Summary
Touchy storm slabs are likely on Friday.
On Wednesday, we received numerous reports of reactive wind slab avalanches mostly up to size 1.5 and several larger ones up to 2.5 from alpine features. These wind slabs ran naturally and were easily triggered by the weight of a skier. Explosive control done also initiated some larger persistent slabs up to size 2.5.
Last week, near-daily reports came in of human-triggered persistent slab avalanches on the January 30th weak layer, with the associated surface hoar layer taking both recreationists and professionals by surprise. Reactivity has begun to taper but this buried weak layer should not be taken lightly as it may now present a low-probability, high-consequence problem. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks and on steep convexities.
Snowpack Summary
15 cm to 20 cm of recent storm snow is expected to bond poorly to the old snow surface. This old surface is comprised of near-surface faceting, surface hoar growth overlying a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline.
Below this, from 60-80 cm down exists a weak layer (surface hoar. facets, crust) that was buried at the end of January. This surface hoar has been the dominating feature in the past few weeks and remains reactive creating surprisingly large avalanches. This is most prominent in sheltered openings at treeline and below treeline.
The facet/crust layer that formed in early December is now buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer.
Terrain and Travel
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Surface hoar distribution is highly variable. Avoid generalizing your observations.
Problems
Storm Slabs
The new storm snow will likely have a poor bond to the underlying old snow surfaces. Storm slabs will be reactive, especially on leeward slopes where deeper and stiffer slabs exist due to wind loading.
Dry-loose avalanches may be seen from steeper slopes, especially where a firm crust exists below the new snow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A weak layer formed in late January may be found 40 to 80 cm deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.
This surface hoar layer has been the culprit of several large human-triggered avalanches in the past week and remains a concern, especially in sheltered areas at treeline. Terrain features to be particularly cautious around include the lee side of ridges, openings in trees, cut blocks, and burns, especially on Northerly aspects where the layer may not be capped by a firm crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 18th, 2022 4:00PM
