An unusual weather pattern could bring heavy snowfall and push us past the tipping point for large natural avalanches. Stick to simple terrain and avoid overhead hazards.
Confidence
Low - Forecast snowfall amounts are uncertain
Weather Forecast
Clashing fronts make for difficult forecasting the next few days. A Pacific warm front and an Arctic cold front are converging over the Rockies, creating the potential for some surprise accumulations of low density snow. Timing, location, and intensity are highly uncertain and so are the estimate snowfall amounts.SATURDAY: Flurries starting Friday night with accumulations of 10-25 cm possible by Saturday afternoon, strong northwest wind, cooling throughout the day with alpine high temperatures around -5 C.SUNDAY: Cloudy in the morning with snow resuming in the afternoon, heavy accumulations possible into Sunday evening (10-30 cm?), strong west wind, alpine high temperatures around -10 C.MONDAY: Cloudy with isolated flurries, light wind, alpine high temperatures around -10 C.
Avalanche Summary
A few small wind slabs were triggered in lee terrain by skiers on Thursday and Friday as storm snow accumulated. The slabs occurred in the top 20 cm of new snow. A few natural wind slabs up to size 2 were also reported throughout the region.A few large persistent slab avalanches that released during last weekend's storm were observed this week. These avalanches failed on deep weak layers from November and December, resulting in large avalanches (size 3). Most were triggered by cornices falling on north and east facing slopes. The incoming storm has potential to trigger similar large avalanches, especially given with strong winds in the forecast.
Snowpack Summary
Expect waves of fresh snow over the next few days as storm snow accumulates. The distribution will be spotty, as some areas already have 30 cm and others nothing. Stay aware of the condition of the new snow. Mostly low density powder is expected, but could become heavy if it warms up. Strong winds will promote slab development in exposed terrain.The lower snowpack in this region is weak, with a number of concerning weak layers. A layer buried mid-January is composed of surface hoar on sheltered aspects and a sun crust on solar aspects was and is now 30-50 cm deep. Another surface hoar layer from early-January is buried 40-60 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 60-80 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the bottom of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.