Avalanche Forecast

Archived

Jan 22nd, 2014–Jan 23rd, 2014

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Northwest Inland.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Thursday through Saturday: A mix of sun and cloud with no precipitation expected. Light alpine winds. Freezing levels reaching 3000m or higher, with alpine temperatures reaching +5C, but a temperature inversion should keep valley bottoms cooler.

Avalanche Summary

Reports from Tuesday include a recent Size 2 natural storm slab avalanche that ran on a buried crust on NE aspect at 900m. Otherwise no new avalanches have been reported.

Snowpack Summary

Approximately 5 to 25cm (elevation and drainage dependant) of recent storm snow sits on various old snow surfaces including crusts. Previously strong winds have resulted in highly variable snowpack depths in exposed areas with deep drifts, scoured areas, and sastrugi. The surface snow is likely undergoing melt-freeze cycles particularly on sun-exposed slopes and at lower elevations. The surface hoar persistent weakness buried early January is most prevalent down approximately 50cm on sheltered slopes at treeline. Professionals continue to keep an eye on the basal facets which can be found down near the ground.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.