Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Wednesday night: Cloudy, 2-5 cm of snow, moderate northwest winds, alpine temperatures -5 C with freezing levels dropping below 500 m. 

Thursday: Increasing cloud, isolated flurries with a trace of accumulation, moderate southwest winds, alpine high temperatures around -7 C with freezing levels around 700 m.

Friday: Cloudy, 10-20 cm of snow, moderate to strong southwest winds, alpine high temperatures near -1 C with freezing levels rising to 2000 m overnight.

Saturday: Cloudy, 5-10 cm of snow, moderate southwest winds, alpine high temperatures around -2 C with freezing level dropping from 2000 m to below 500 m overnight.

A widespread natural avalanche cycle occurred Wednesday. Numerous, large (size 2-2.5) natural and human-triggered avalanches were observed failing on the storm snow interface comprised of a recent layer of surface hoar down 40 cm. Check out this MIN and this MIN, both from earlier in the storm cycle on Tuesday, that illustrate this recent avalanche activity.

Several persistent slab avalanches (size 1.5-3), both human and explosive-triggered, were reported over the weekend. These avalanches released on both the December surface hoar and November crust layers across a variety aspects. This recent persistent slab avalanche was observed Sunday. It scrubbed into the lower snowpack and to the ground and was noted for being triggered on a shallow, rocky, convex slope.

The possibility for large human-triggered persistent slab avalanches remains a serious concern, especially as sensitive storm slabs create the potential for avalanches to step-down to these layers.

Storm snow totals came to 30-60 cm for most of the region, creating a widespread, reactive storm slab problem. At higher elevations, strong southwest winds are expected to exacerbate the reactivity of the new snow in drifted areas. The storm covered another recent layer of surface hoar and a sun crust on steep sun-exposed aspects. 

Buried deeper in the snowpack, there are multiple weak layers, which include a feathery surface hoar layer (down 80 to 120 cm), an older surface hoar layer with a melt-freeze crust on steep south aspects (down 100 to 140 cm), and a layer of sugary faceted snow, surface hoar, and melt-freeze crusts from late November found in the bottom half of the snowpack. 

Snowpack tests continue to produce sudden and propagating results on these layers (like this MIN from Big White on Sunday and this MIN from Rossland on Monday) This fundamentally unstable snowpack structure remains a serious concern as the recent loading from new snow and wind has added significant stress to these weak layers.

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Avoid freshly wind loaded terrain features.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.