Our persistent slab problem is evolving into a low probability/high consequence scenario where you may not get feedback from a bad decision. The formation of new wind slabs will add a layer of complexity to your terrain selection on Friday.
Light new snow amounts combined with increasing winds are expected to form small but touchy new wind slabs that will need to be managed on Friday. Expect this problem to increase with elevation and to be most pronounced in the immediate lee of wind-exposed terrain features. Wind slabs perched above shallow, rocky areas have potential to trigger a deeper weak layer to create a large avalanche.
Several different weak layers can be found in the snowpack, they are now deeply buried, and they have recently produced large avalanches. Persistent slabs are gradually becoming less likely to trigger, but it remains prudent to assume these layers are present, reactive to human triggers, and capable of forming very large, destructive avalanches.
Thursday night: Cloudy with isolated flurries bringing a trace to 5 cm of new snow. Light to moderate southwest winds increasing into Friday.
Friday: Cloudy with isolated flurries and a trace of new snow. Moderate to strong west winds shifting northwest. Alpine high temperatures around -8.
Saturday: Mainly cloudy. Light to moderate west winds. Alpine high temperatures around -7.
Sunday: Mainly sunny. Light north winds. Alpine high temperatures around -4.
A recent large (size 2) skier-triggered persistent slab avalanche was observed in the Kelowna area on Wednesday. It featured a 30-70 cm crown fracture, scrubbed into the lower snowpack, and was noted for being triggered on a shallow, rocky, convex slope.
Several more large persistent slabs were triggered with explosives control in the Nelson area on Monday. These slabs featured crown depths of 15-120 cm, giving some evidence of wind loading. These avalanches are suspected to have released on our early November facet/crust layer, which exists below two other persistent weak layers of concern.
A widespread avalanche cycle occurred on Saturday, with observations of large artificially triggered avalanches continuing into Sunday. Large avalanches were observed on all aspects, generally above 2000 m. Numerous other large to very large avalanches were also triggered by explosives on the late-November layer described in our Snowpack Summary.
The stormy period that ended early this week saw around 70 to 100 cm of snow deposited in the region. This snow brought a significant load to multiple weak layers, including:
Although avalanche activity on these layers has been declining since the storm, they each continue to produce concerning snowpack test results and they are expected to heal slowly.
With this in mind, it remains prudent to make terrain decisions with the understanding that one or more of these deeply buried layers are present and could produce a large and destructive avalanche with a human trigger.
