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Avalanche Forecast

Archived

Mar 14th, 2014–Mar 15th, 2014

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

For more insight into the current tricky conditions, see the latest Forecasters Blog.

Confidence

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

Saturday: Mainly cloudy with scattered flurries bringing 5-10 cm depending on drainage. Mostly light westerly winds with strong gusts associated with snow flurry activity. Freezing levels as high as 2000 m in the far south, but 1500 m in the north. Sunday: Cloudy with flurries bringing 10-20 cm depending on drainage. Generally moderate but gusty westerly winds. Freezing levels dropping slightly to 1800 m in the south and hovering at 1500 m in the north. Monday: A mix of sun and cloud with isolated flurries, but I would'nt be surprised if some drainages got another 10-20 cm. Generally light westerly winds gusting with flurry activity, and freezing levels down to 1400 m.

Avalanche Summary

Expect fresh wind slab and loose dry snow avalanche activity to increase throughout the forecast period as snow flurries load exposed alpine and treeline feature. At treeline elevations and below, significant warming has made large persistent slab avalanches are highly sensitive to human triggers. In parts of the forecast area, very large destructive avalanches running to valley bottoms from major start zones remain a  concern. Neighboring forecast regions have recently reported large avalanches initiating in the new storm snow, then stepping down to deeper layers, some running full path to the ground. Cornice failures triggering large deep persistent avalanches have also been reported.

Snowpack Summary

A 50-70 cm slab is bonding poorly to buried surface hoar and facets particularly on sheltered slopes such as cut blocks, and crust on previously sun-exposed slopes.  Warm temperatures and sun-exposure has been making these and deeper persistent slabs very sensitive to triggers at treeline elevations and below, and resulting in surface melt-freeze cycles as high as alpine elevations. The deeper facet/crust persistent weakness buried at the beginning of February, now down 60 to 160cm, has been described by avalanche professionals as "very weird". Although widespread, it has been highly variable in terms of reactivity. Convective flurry activity has already accumulated 10-15cm of fresh snow in some drainages, which has likely blown into touchy wind slabs on leeward slopes. Weak basal facets exist in many areas, but without a large load, triggering now is unlikely.

Problems

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.

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.