Avalanche Forecast
Regions: Haines Pass.
Hunting dry snow on high north aspects puts you in the same terrain where it's possible to trigger a destructive slab. Manage the problem by choosing simple terrain free from overhead hazard.
Confidence
Moderate
Avalanche Summary
Riders saw evidence of recent large persistent slab avalanches and we received many reports of whumpfing (e.g., here). The avalanche observations add to the many natural and rider-triggered avalanches that released a week ago in alpine terrain. These weak layers may take some time to strengthen, meaning they may remain active to the weight of a person or machine for the foreseeable future.
Please consider sharing your observations to the Mountain Information Network.
Snowpack Summary
Recent strong wind has produced wind-affected snow in the alpine. Soft, settled snow may still be found in wind-sheltered terrain in the alpine. The snow surface on sun-exposed slopes will become moist or wet during the day and freeze into a hard melt-freeze crust overnight.
Weak layers of surface hoar crystals and/or faceted grains may be found around 30 to 70 cm deep in the snowpack. These problematic layers may be associated with a hard melt-freeze crust above or below. These layers were the culprit of many large avalanches last week and remain unstable in snowpack tests.
Cornices are large and looming at this time of year.
Weather Summary
Thursday night
Clear skies. 20 to 30 km/h southeast ridgetop wind. Above 0 °C temperatures at ridgetop with an above freezing layer forming between 1500 - 2400 m.
Friday
Clear skies with possible valley cloud below 1500 m. 20 to 30 km/h southeast ridgetop wind. Treeline temperature 2 °C with an above freezing layer persisting between 1500 - 2000 m.
Saturday
Becoming mostly cloudy. 10 - 20 km/h east ridgetop wind, easing. Treeline temperature +1 °C. Above freezing layer dissipated with freezing level to 1500 m in the afternoon.
Sunday
Cloudy with continuing scattered flurries from overnight bringing less than 3 total cm of new snow. 10-15 km/h south ridgetop wind, increasing. Treeline temperature around 0 °C with freezing level to 1300 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Choose conservative terrain and watch for clues of instability.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Cornice failures could trigger very large and destructive avalanches.
- The more the snow feels like a slurpy, the more likely loose wet avalanches will become.
Avalanche Problems
Persistent Slabs
Weak layers of facets and/or surface hoar are buried 30 to 70 cm deep. They are most prominent on alpine features sheltered from the wind. There are recent observations of whumpfing and large avalanches occurring on these layers.
Aspects: North, North East, East, West, North West.
Elevations: Alpine.
Likelihood: Possible - Likely
Expected Size: 1.5 - 2.5
Loose Wet
Wet loose avalanches could occur on steep sun exposed slopes with daytime warming. Cornices are also large and weaken with warming.
Aspects: South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2