Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Regions
South Rockies.
Touchy wind slabs can be triggered by the weight of a person or snowmobile.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
SUNDAY: ~5 cm light dry snow. Freezing level near 1000 m. Moderate to strong south-westerly winds.MONDAY: Mix of sun and cloud. Freezing level near 700 m. Moderate west to north-westerly winds. TUESDAY: 5-10 cm snow. Freezing level near 1000 m. Moderate to strong south-westerly winds.More details can be found in the Mountain Weather Forecast.
Avalanche Summary
Snowmobilers triggered size 1.5 and size 2 wind slabs in the Crowsnest area on Saturday. On Friday, evidence of a persistent slab avalanche cycle from earlier in the week was observed near Mear Lake.On Thursday, observations of some very large slabs were made in the North Elk valley. These are thought to have failed within the last week. Whumpfing was reported at treeline in the North Elk valley as well.It is still possible to trigger a surprisingly large wind slab or persistent slab with the weight of a person or sled, especially from a convexity or thin snowpack area.
Snowpack Summary
Touchy new wind slabs were found on Saturday in the Crowsnest area. These are expected to continue to build over the next few days. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Wind slabs overlie various surfaces, including older hard wind slabs, crusts, facets and spotty surface hoar.The lower snowpack is weak with two primary concerns:1) A widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.2) A rain crust with sugary facets buried in late November near the bottom of the snowpack.Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.