Regions
Kootenay Boundary.
Enjoy the last of the cold snow Monday, Tuesday looks to be quite warm. Remember that prolonged direct sun on any slope may initiate a round of large natural avalanches.
Confidence
Fair - Freezing levels are uncertain on Tuesday
Weather Forecast
Synopsis: An upper ridge passes over the region Monday ahead of a pacific frontal system that should spread precipitation over the western portion of the region Monday night, impacting the rest of the region Tuesday. Looks like the freezing level will rise to a more, spring like, 1800m Tuesday, lowering back down Wednesday as the region picks up some precipitation.Monday: Freezing Level: 1300m -1500m; Precipitation: Nil; Treeline Wind: Light, SE | Ridgetop Wind: Moderate, WTuesday: Freezing Level: 1300m - 1800m; Precipitation: 0:5mm - 0:5cm; Treeline Wind: Light, S | Ridgetop Wind: Moderate, SW Wednesday: Freezing Level: 1300m - 1600m; Precipitation: 4:12mm - 4:15cm; Treeline Wind: Light, SW | Ridgetop Wind: Moderate, W
Avalanche Summary
The bulk of the avalanche activity on Saturday was limited to sluffing in steep terrain. Skiers in the region managed to intentionally ski cut avalanches to size 1.5 on east facing slopes with crowns up to 40 cm in depth. Explosive control work with large amounts of explosives resulted in similar avalanches. It should be noted that nothing stepped down into any of the deeper persistent weaknesses. On Friday the strong sun heated the upper snowpack resulting in a natural cycle to size 2 on south and southeast facing slopes. Ski cuts on shady aspects produced avalanches to size 1.5. On Thursday a widespread natural avalanche cycle to size 2.5, averaging size 1.5 was reported. There were no reports of anything stepping down below the March 10th crust into the deeply buried persistent weak layers.
Snowpack Summary
5 - 10 cm of convective snowfall from Saturday night brings snow totals from the last week to 25 - 50cm of light density snow. This makes for 55 - 80cm on top of the March 10th crust. This crust is widespread to 2000m across the region, perhaps even higher on solar aspects. It's mostly supportable, we've received reports of it being as thick as 15cm in the south of the region, but it varies in thickness and supportability. As you head north in the region where the mountains are higher (and temperatures were colder when the crust was forming), this crust is less likely to exist. If you're heading to the north or the region, it's worth checking out the South Columbia bulletin too.A facet/crust persistent weakness buried at the beginning of February, now down 70 - 200cm, has been highly variable in terms of reactivity but still shows 'sudden' results in some snowpack tests. In areas where the strong and supportive March 10th crust exists, triggering this layer has become unlikely. That said, this layer is still difficult to trust and any avalanche at these deeper, persistent interfaces would be large and destructive.,
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.