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Avalanche Forecast

Archived

Feb 9th, 2013–Feb 10th, 2013

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

Regions

Purcells.

Intensity from the sun can make the snowpack weaken and the avalanche danger rise rapidly. Be aware of this and keep travel options open to adjust with this change.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

Sunday: As the ridge shifts to the East, the region will remain under a NW flow which will keep alpine temperatures cooler but under a high solar influence. However, some areas may still see high cloud cover through the day. Ridgetop winds will blow Light out of the North. Treeline temperatures near-1 and freezing levels rising to 1400 m.Monday: The flattening ridge will start to retreat to the South allowing a more zonal flow to set up off the coast. Ridgetop winds will switch and blow moderate from the West. Treeline temperatures will be near -2 and freezing levels near 1300 m.Tuesday: A cold front embedded in the zonal flow will move through the region bringing light precipitation amounts accompanied by strong winds from the SW. Treeline temperatures will fall to -6 and freezing levels will be near 1200 m.

Avalanche Summary

Over the past couple of days a few natural slab avalanches occurred on steep solar aspects up to size 2.5. On Friday a skier triggered size 1.5 slab avalanche occurred from a NE aspect at 2300 m and natural loose dry sluffing continues from steep unsupported terrain.

Snowpack Summary

Wind slabs exist in the alpine and at treeline on lee slopes and behind ridgelines. The recent storm slab continues to settle over old interfaces comprising of surface hoar, crusts and facets down 30-50 cm. However, areas that have buried surface hoar seem to be most touchy. Continued freezing temperatures overnight have helped to strengthen the snowpack at lower elevations. The mid-pack is generally well settled and the average snowpack depth at treeline elevations is near 130. Watch the duration and intensity of the sun in your local riding area; it may weaken the upper snowpack. Cornices have grown and may threaten slopes below.

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.

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.