Newly formed storm slabs are expected to be touchy on Tuesday. The region continues to deal with a tricky persistent slab problem and very large avalanches remain possible. Conservative terrain selection remains critical.
A persistent slab problem formed by a crust down 70-200 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
Storm slabs are expected to remain very reactive to human triggering on Tuesday, especially in wind loaded terrain. These slabs overlie a weak interface and may remain touchy for an extended period.
Unsettled conditions are expected on Tuesday in the wake of the storm. Periods of light snow and sunny breaks are both possible.
Monday night: Snowfall 5-15 cm, moderate to strong SW wind, treeline temperature around -8 °C.
Tuesday: A chance of sunny breaks in the morning, light snow in the afternoon 3-6 cm, light to moderate SW wind, treeline high around -10 °C.
Wednesday: A mix of sun and cloud with a chance of flurries in the morning, light to moderate N wind, treeline high around -20 °C.
Thursday: Periods of light snowfall 2-4 cm, moderate to strong SW wind, treeline high around -14 °C.
Early reports from Monday include explosive triggered storm slabs up to size 2. Ski cutting was triggering size 1 storm slabs and loose dry avalanches.
On Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This MIN post goes into more details and has some great photos showing the nature of the problem and the type of terrain where this problem seems most prevalent. On Friday, a size 2.5 persistent slab avalanche was reported on a north aspect at 2000 m elevation. This failed on the early December weak layer down 100-175 cm. Last week, a few surprisingly deep older crowns were observed between Fernie and Sparwood. These persistent slab avalanches also likely ran on the early December crust.
On Tuesday, recently formed storm slabs are expected to remain reactive to human triggering. These new slabs sit on a weak interface and may be very reactive, especially in wind loaded terrain. The persistent slab problem remains a serious concern and the weight of the new snow may increase the reactivity of these deeper layers. Smaller storm slab avalanches also have the potential to step down to deeper layers resulting in very large avalanches.
The new storm snow buried a variable snow surface which is likely weak and includes widespread facets, wind affected surfaces, and/or surface hoar in sheltered areas. The new snowfall may have been accompanied by moderate to strong winds and new storm slabs are expected to be most reactive in wind loaded areas.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-200 cm. Activity on this layer has been sporadic, but most recently produced large avalanches on January 2 and December 31. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
