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Avalanche Forecast

Archived

Jan 6th, 2015–Jan 7th, 2015

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 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.

Regions

Sea To Sky.

Tricky conditions are expected for Wednesday with a new storm slab sitting on a potentially touchy weak layer. Don't let the warm air and sunny conditions make you over confident.

Confidence

Fair

Weather Forecast

A ridge of high pressure should keep the south coast dry for the next three days. Wednesday should be mostly sunny with light alpine winds and freezing levels around 3000m. A temperature inversion is expected and the warmest air (+5 deg C) is expected to sit around 2000m. Similar conditions are expected on Thursday with freezing levels around 3000m, a mix of sun and cloud, and light winds. On Friday, mostly cloudy conditions are expected with freezing levels beginning to fall progressively. The next weak storm system is currently forecast to arrive Friday night and it looks like freezing levels will be back down around 1000m.

Avalanche Summary

Reports from Tuesday of natural and explosive triggered slab avalanches up to size 2.5 on leeward slopes.  Loose activity was also reported on steep solar aspects. On Monday, natural storm slabs up to size 2 were reported. Loose activity was also reported where it rained. On Sunday, widespread natural and skier triggered activity was reported to size 1. On Wednesday, natural activity is expected to decrease but may still occur due to warming and/or solar radiation. Skier triggered avalanches remain the primary concern for Wednesday as the slab may still be touchy.

Snowpack Summary

At the end of the storm, freezing levels rose to around 2000m and rain fell on the new storm snow. The storm slab is around 60cm thick and sits on a previously variable snow surface that included wind affected surfaces (crust, hard and soft slabs), a freezing rain crust or sun crust, and surface hoar or sugary facets in sheltered terrain. The bond between the storm slab and the layer below is currently unknown but is expected to remain reactive on Wednesday. Cornices are expected to be weak with the current warming. In the middle and lower snowpack we might find the mid-December surface hoar or crust/facet weak layers. These are now buried 1m or more. The surface hoar layer may be found in sheltered shady areas at and below treeline, while the crust/facet layer is expected to be more widespread but also more variable. Prior to the storm, reports suggested that the layer could be between 0 and 120cm deep depending on exposure to wind. The new storm load means these deep layers may be more reactive than prior to the storm.

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.

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.

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.