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Avalanche Forecast

Archived

Apr 20th, 2014–Apr 21st, 2014

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

Regions

Purcells.

At this time of year resist the urge to rely on danger ratings alone. Daytime warming or periods of sun can rapidly elevated danger ratings above what is forecast. Check out this blog post for more info on how to manage risk during the spring.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Synopsis:  A weak ridge of high pressure will shift eastwards as the next system moves in over the region Monday night with precipitation forecast for Tuesday and Wednesday.Tonight and Monday: Partly cloudy with a chance of wet flurries /  Moderate southerly winds / Freezing levels 2000 - 2500m Tuesday: Flurries (5-15 cm) / Light southerly winds / Freezing levels 1900 to 2400m Wednesday: Flurries (5-20cm) / Light westerly winds / Freezing levels 1500 to 2000m

Avalanche Summary

In areas where the upper snow is moist and sits above a crust small wet slabs have been triggered by skiers.  At lower elevations and on solar aspects small to large loose wet avalanche continue to be triggered on steep slopes. Cornices collapses have been reported during periods of daytime warming. Occasionally these heavy triggers have caused large deep slab avalanches on the slopes below.

Snowpack Summary

The region has recently received between 10 and 30cm of new snow with snowline currently sitting somewhere around 1100m.  Below the recent snow a melt-freeze crust can be found on all but high elevation North aspects. Moderate winds have affected all Wind slabs can be found in lee features on N and E aspects in the Alpine.Several persistent weak layers still exist in the highly variable snowpack of the Purcells:-The mid-March sun crust/surface hoar layer down 50-80cm and the early-March crust/facet/surface hoar layer down around 80-120cm seem to be laying dormant for the time being.-The mid-February crust/facet/surface hoar combo is typically down 60 - 120cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up. The resulting avalanche would be very large and destructive.- Weak basal facets can be found in many areas, however triggering this layer is unlikely.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.