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Avalanche Forecast

Archived

Nov 17th, 2011–Nov 18th, 2011

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
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 variation in conditions and danger levels are likely to exist. To produce more accurate forecasts, we need information. Please send an email to [email protected].

Confidence

Poor - Due to limited field observationsfor the entire period

Weather Forecast

Friday and Saturday: Mostly clear with freezing levels around 200m and light northwesterly winds. Light flurries possible for coastal areas on Friday.Sunday: Increasing clouds with light flurries and light southwesterly winds.

Avalanche Summary

Recent reports include wind slab avalanches up to Size 2.5 failing on a surface hoar layer that was buried earlier this week. Some slabs were up to a metre deep and pulled back into low angled terrain on ridges showing incredible propensity for propagation. Wind and storm slabs will likely remain susceptible to human triggering throughout the weekend, and probably much longer in areas where they're failing on surface hoar a facet/crust combination.

Snowpack Summary

Another 20-30cm of upside-down storm snow brings total snowpack depths up to a metre or so in sheltered treeline areas, but expect to find much deeper pockets of wind-blown snow immediately down-wind of terrain features and ridge crests. A thick rain crust from last week is 70 or 80 cm off the ground at treeline and lower alpine elevations, with facets above and below in some locations. Above that is a buried layer of surface hoar that formed during the clear weather over the weekend. These weaknesses now have a sufficiently thick and cohesive slab to produce avalanches in most areas and they have all the characteristics of an avalanche problem that could persist for extended periods.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.