Avalanche Forecast

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, light to moderate northwesterly winds, low treeline temperatures near -5 C with freezing level at valley bottom.

Tuesday: Increasing cloudiness with snow starting at night, 25 to 40 cm overnight, moderate to strong southwesterly winds, high treeline temperatures around -5 C with freezing level rising to 1000 m by the end of the day.

Wednesday: Snow, heavy at times, 25 to 45 cm, strong to extreme southwesterly winds, high treeline temperatures near -3 C with freezing level around 1000 m.

Thursday: Mainly cloudy with isolated flurries, 5 to 10 cm, moderate to strong southwesterly 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 to likely in wind affected areas on Tuesday. Avalanches in the recent snow have the potential to step-down to recently reactive buried weak layers, with the potential to produce very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below. 

On Sunday, operators reported several large (size 2-2.5) explosive-triggered avalanches releasing 50-75 cm deep in the recent storm snow. We aslo areceived reports of large (size 2-3) avalanches that released on a persistent weak layer on northeast, northwest, southwest aspects between 1700-1900 m. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls. It may still be possible to trigger very large avalanches in isolated areas of the region on Tuesday.

Last weekend's powerful storm brought 40-70 cm of snow to the mountains. 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 100-180 cm). This layer seems particularly reactive at treeline elevations, between 1600-2100 m. On Sunday, this persistent slab problem produced a large size 3 avalanche triggered by a snowmobiler in Brandywine area 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.