Avalanche Forecast

Archived

Feb 18th, 2012–Feb 19th, 2012

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 Columbia.

Confidence

Good

Weather Forecast

We're entering a more active pattern which should persist through the middle of next week.Sun: A ridge of high pressure rebuilds during the day allowing temperatures to cool slightly while winds ease and switch from the SW to NW. A bit of instability from Saturday's storm will produce the odd flurry, but skies should clear in the afternoon. Look for 1500m temps to climb to -2 during the day.Mon/Tue: A few weak systems pass over the region favoring west slopes. Nothing in the flow is particularly well organized, it's the kind of setup that has the potential to bring 5-10 cm a day. Precip totals will be quite variable throughout the region. 1500 m temps: High -3, Low -7

Avalanche Summary

Activity continues to be limited to thin windslabs in wind exposed locations and sluffing in wind sheltered locales.

Snowpack Summary

Five centimeters fell overnight Friday which makes for 10 of light density snow above the February 16th Surface Hoar. 20 cm of light density snow lies between the February 16th surface hoar and the February 8th weakness. Within that 20cm some places have at least one other layer of surface hoar that formed between snowfalls. Feb. 8th is used to describe a combination of weak layers: In most locations it marks a widespread surface hoar layer. On steep south & west facing aspects a crust that formed during the drought was also buried on Feb. 8th. This crust likely has a bit of faceting below it too, meaning that most terrain in the region has a weak layer 20 - 25 cm under the snow surface. Down below this problematic interface a well settled mid pack is in place. The exception is the eastern and southern parts of the region where deeper weaknesses and basal facets may still be a factor. In these areas, a low-probability/high-consequence condition exists. It should be noted that large cornices remain widespread throughout the region.

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 Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.