More snow and strong wind will result in 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 estimated snowfall amounts.SATURDAY: Flurries starting Friday afternoon will deliver a moderate amount overnight and continue throughout the day (10-25 cm?), strong northwest wind, freezing level 1200 m in the morning then dropping with alpine high temperatures around -4 C.SUNDAY: Snow resuming Sunday morning with heavy accumulations possible throughout the day and into Sunday evening (20-50 cm?), strong west wind, alpine high temperatures around -4 C.MONDAY: Flurries easing off over the day, decreasing wind, alpine high temperatures around -12 C.
Avalanche Summary
On Friday, storm snow was very reactive to ski cutting and explosives, producing many 20-40 cm thick storm slabs. Poor visibility obstructed alpine views, but natural activity was likely at higher elevations.There was a brief break in persistent slab avalanche activity this week. However, on Monday and Tuesday, many large (size 2-3) avalanches were triggered naturally and with explosives. Most of the natural avalanches were triggered by cornices falling and releasing slabs on the December and November layers, producing 150-250 cm thick crowns. This type of activity has been occurring on a regular basis for the past month, and the incoming storm has potential to produce more of the same.
Snowpack Summary
Expect waves of fresh snow over the next few days as storm snow accumulates. Stay aware of the condition of the new snow. Mostly low density powder is expected, but could become heavy if it warms up. Also expect slab development in wind affected areas. The new snow sits above a breakable crust up to 1700 m. For the past month we have seen regular avalanche activity on multiple deep weak layers. A layer buried mid-January is composed of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and a sun crust on solar aspects and is now 60-80 cm deep. Another surface hoar layer from early-January is buried 90-110 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 120-160 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the bottom of the snowpack and up to 200-250 cm deep. The bottom line is the snowpack structure in this region is weak. Human triggering is most likely on the shallower weak layers, but any avalanche has the potential to step down to deeper layers and become much larger.
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.