Avalanche Forecast

Archived

Nov 25th, 2012–Nov 26th, 2012

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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Sea To Sky.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecaster's blog for further details on interpreting early season bulletins.

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: A ridge of high pressure over southern BC should give mainly sunny skies for Monday and Tuesday. The ridge should break down on Wednesday allowing a mild frontal system to push in. Monday: A mix of sun and cloud. Freezing level near surface with a potential above freezing layer developing. Winds are light and variable. Tuesday: A mix of sun and cloud. Freezing level at around 2500 m. Winds light from the northwest. Wednesday: Increasing cloud with precipitation developing. Freezing level around 1800-2000 m.

Avalanche Summary

Recent observations are from the Whistler area: Several natural avalanches up to size 2 were observed during the storm on Friday and Saturday morning. Most of these avalanches failed within or below the storm snow. Recent avalanche control did produce isolated results up to size 2.5 that failed on the early November crust/facet layer. Of note, there was a report of a size 2.5 skier triggered avalanche on Saturday. This avalanche occurred on a northeast aspect in the alpine. It was triggered from the bottom of the slope, and likely released on the early November layer.

Snowpack Summary

The main snowpack feature worth noting is a rain crust buried in early November that is now down around 80 cm at treeline and as deep as 150 cm in alpine areas. A weak layer of facets on top of and within this crust is worth remaining suspicious about (sudden collapse fracture character in snowpack tests showing propagation potential). Widespread whumpfing and cracking on this layer has also been reported from the Whistler area. Because this weakness is so close to the ground in most areas, associated avalanche activity will likely be limited to slopes with smooth ground cover (e.g. scree slopes, rock slabs, summer firn, glaciers, etc.). The total snowpack depth at treeline is around a 120 cm. Alpine areas are deeper but more variable. Most slopes below treeline are still below threshold depths for avalanches. For more information check out the telemarktips.com forum , the Mountain Conditions Report, and Wayne Flann's Avalanche Blog.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.