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Avalanche Forecast

Archived

Dec 14th, 2011–Dec 15th, 2011

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

South Rockies.

Confidence

Fair - Due to variable snopack conditions

Weather Forecast

Thursday: Flurries with a couple cm's of snow during the day. The winds will be moderate blowing from the west. Freezing levels will remain at valley bottom. Friday/Saturday: Sunny skies. Treeline temperatures near -10. Moderate westerly ridgetop winds.

Avalanche Summary

Numerous rider triggered size 1 slab avalanches reported. These avalanches initiated from firm of pockets of wind slabs. They occurred on north-northwest aspects around 2100m.

Snowpack Summary

Up to 15cm of new snow fell earlier in the week. Beneath this new snow sits surface hoar up to 10mm in size. The surface hoar can only be found in sheltered areas. The strong wind that has been ripping through the region has kept the SH in check at upper elevations and exposed areas at treeline. This is a minor issue for the short term, but could be a significant player in the long term; this will be a layer to watch. It may not be reactive with 15cm, or will it? With drips and drabs in the forecast it makes it difficult to predict if, and/or when this layer may fail and initiate an avalanche cycle. The snowpack depth is still variable through the region. In upper elevations there are reports of up to a meter. The surfaces consist of firm wind slabs, surface hoar, and facetted (sugary) snow. Below the surface the mid pack seems to be holding strong. We are still concerned with the weak basal layers (rain crusts, facets) that exist at the bottom of the pack. The snowpack overall is still pretty thin. With numerous avalanches failing on this layer in the Rockies proves that there is still a chance for full depth avalanches to occur. When riding a slope try to avoid thin spots like small trees, shrubs or rock outcrops. These may react as trigger points, and initiate a deeper instability.There is a new Forecaster Blog Post today. It discusses "Dribs and Drabs" how incremental loading patterns will effect our snowpack. Please click the tab at page left.

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.