South Coast Inland

Developing wind slabs and a buried weak layer create complicated conditions requiring a cautious approach, appropriate terrain selection and diligent decision making.

A low pressure centre coming from the Gulf of Alaska will bring increasing cloudiness on Tuesday and significant snowfalls starting at night.

Monday night: Clear periods, ligth to moderate westerly winds, low treeline temperatures near -10 C with freezing level at valley bottom.

Tuesday: Increasing cloudiness with snow starting at night, 10-20 cm overnight, strong to extreme southwesterly winds, high treeline temperatures near -5 C with freezing level going up at 600 m.

Wednesday: Snow, heavy at times, 10-15 cm, strong to extreme southwesterly winds, high treeline temperatures near -5 C with freezing level at 700 m.

Thursday: Mainly cloudy with flurries, 5-10 cm, light to moderate westerly winds, high treeline temperatures near -10 C with freezing level at valley bottom.

With recent storm snow available and southwesterly winds picking up overnight and increasing during the day, natural and triggered avalanches will be possible in wind affected areas on Tuesday. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below.

In the neighbouring Sea-to-Sky region, we received reports of large (size 2-3) persistent slab avalanches on northeast, northwest and southwest aspects between 1700-1900 m. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls.

Last weekend's powerful storm brought 20-30 cm of new snow, with favored areas near the Coquihalla seeing upwards of 60-70 cm. Strong south winds will continue to redistribute the new snow into dense wind slabs that will be possible to trigger at upper elevations, especially where the new snow is poorly bonded with the old snow. The recent snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Stay alert to changing slab conditions as you move into wind-exposed terrain, and monitor the bond of the new snow to the old snow surface.

A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-160 cm). This layer seems particularly reactive at treeline elevations between 1700-2100 m and in the north of the region in areas such as the Hurley. On Sunday, this persistent slab problem produced a large size 3 avalanche triggered by a snowmobiler in the neighbouring Sea-to-Sky region with smaller remotely-triggered avalanches. This problem is particularly hard to predict and tricky to manage. Given the rapid load from new snow and wind along with recent avalanche activity, this persistent slab problem requires wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog.

• Choose conservative terrain and watch for clues of instability.
• Cornice failures could trigger very large and destructive avalanches.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
• Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.