Recent storm snow has been reactive on steep slopes. Buried weak layers increase the potential size of avalanches.
Summary
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Friday: around 5 cm new snow. Freezing level 600 m. Westerly ridgetop winds gusting to 40 km/h.Saturday: 10-15 cm new snow. Treeline temperature around -8C. Winds southwesterly 30km/h.Sunday: Clearing, but lingering flurries possible. Treeline temperatures around -15C. Winds light northeasterly.
Avalanche Summary
On Wednesday, a few small avalanches, including one involving a skier, were reported in recent storm snow with crowns approximately 30 cm deep.On Sunday there were a few reports of naturally triggered size 3 persistent slab avalanches on south to northwest facing alpine slopes. These avalanches are suspected to have failed due to wind loading and/or solar inputs. Also, explosive control work continued to produce large, deep avalanches up to size 3 on north to southeast aspects above 2200m. On the same day, a skier is believed to have remotely (from a distance) triggered a size 1.5 avalanche on a northwest aspect at 2800m that failed on the early January layer.On Monday and Tuesday, explosives control continued to trigger persistent slab avalanches to size 3.5 in mainly north to west facing alpine terrain. Although deeper, persistent avalanche activity is becoming less frequent, these avalanches point to the continued reactivity and destructive potential of these layers.
Snowpack Summary
By Wednesday morning up to 15cm of new snow had fallen. I suspect moderate southwest winds shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects and surface hoar on sheltered slopes.Below the snow surface several persistent weak layers make up a troublesome snowpack which is not tolerating recent storm loads. In the top 1-2 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.
jfloyer,
Avalanche Canada
