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Avalanche Forecast

Archived

Dec 20th, 2013–Dec 21st, 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

South Rockies.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Very little precipitation in the forecast for this region. Saturday, Sunday, Monday: A chance of flurries each day, with light snow possibly starting to fall Monday afternoon. Treeline temperatures consistent around -10C. Ridgetop winds moderate from the NW, picking up a little on Monday afternoon.

Avalanche Summary

A few loose dry sluffs were observed on Friday. No Slab avalanches were reported.

Snowpack Summary

There appears to be a lot of snowpack variability across the region. Snowpack depths at treeline seem to vary from 50 - 110 cm with high variability in wind-exposed areas. There are several persistent weak layers which are still being discussed in the region. Nearest to the surface is the mid-December (~Dec 10) facet/surface hoar/crust interface which does not seem to have enough snow on it yet to create a widespread problem. Next is the late-November/early-December interface which is made up of surface hoar, a crust, and/or facets. This layer is typically down 30-70cm and is most likely to pose the biggest problem for the region at the moment. Check out this video of a recent snowpack test on this layer. Despite it's reactivity in snowpack tests, we have not yet seen widespread avalanche activity on this layer. I suspect it only needs a little more additional load to turn this into a more serious avalanche problem. A buried crust from mid-November can be found near the base of the snowpack below 1650 m and is breaking down into facets.

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.