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Avalanche Forecast

Archived

Feb 17th, 2015–Feb 18th, 2015

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

Regions

South Columbia.

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Confidence

Good

Weather Forecast

The dominant ridge of high pressure should maintain a mix of sun and cloud on Wednesday, but looks like it will briefly flatten late in the day allowing more cloud and light precipitation to cross the province on Thursday. The freezing level on Wednesday is between 1500-2000 m, but an above freezing layer may develop higher in the alpine. On Thursday the freezing level dips to around 1500 m. On Friday we should bounce back to a mix of sun and cloud with slightly cooler temperatures. Winds are forecast to be light or moderate from the W-NW throughout the week.

Avalanche Summary

Explosive control work on Monday produced a few size 2-3 slab avalanches. Most of these were from steep alpine slopes and the majority were on southerly aspects. There were also a couple reports of natural and explosive triggered cornice falls, some of which triggered slabs up to size 2 (one stepped down to the November crust). This recent activity suggests that conditions have improved, but large loads (like a cornice fall) could still trigger deeper persistent weaknesses, primarily in alpine terrain.

Snowpack Summary

The snow surface is a mix of surface hoar, crusts, low density snow, or wind affected snow depending on aspect and elevation. The "Valentine's Day" crust is just below the surface and is now strong and thick in most places. At alpine elevations, new wind slabs may have formed from NW winds, and cornices are large and weak. The late-Jan crust/surface hoar layer (up to 100 cm deep) and the mid-January surface hoar (80-120 cm deep) continue to give variable results in snowpack tests. Chances of triggering these weaknesses have decreased, but triggering may be possible from thin or rocky snowpack areas; or perhaps with a cornice fall, or an avalanche stepping down, especially on sun drenched slopes.

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.

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.