Avalanche Forecast
Issued: Jan 4th, 2020 4:30PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Incremental snowfall is out-pacing the snowpack's ability to adjust. Stay vigilant with simple terrain choices as the storm cycle continues.
Summary
Confidence
Weather Forecast
Saturday night: Cloudy, scattered flurries with 2-5 cm accumulation, moderate southwest wind, alpine temperature -7 C.
Sunday: Cloudy, 5-10 cm of snow, moderate southwest wind, alpine high temperature -8 C.
Monday: Cloudy, 10-15 cm of snow, moderate southwest wind, alpine high temperature -5 C.
Tuesday: Cloudy, 20-30 cm of snow, moderate south wind, alpine high temperature -3 C.
Avalanche Summary
Widespread, large (size 2-2.5) natural, human, and explosive-triggered storm slab avalanches were reported across the region on Friday and Saturday. Avalanches were 30-60 cm deep and were reported on all aspects and elevations. Some of these were remotely-triggered (i.e. from a distance).
Three notable persistent slab avalanches released naturally on east and northeast facing slopes above 2200 m in the southern part of the region on a crust/facet layer from late November buried 150 cm deep. These avalanches give clear evidence that the continual loading on this fundamentally weak snowpack structure remains a serious concern.
Snowpack Summary
60-120 cm of new snow has fallen throughout the past week creating a touchy storm slab problem. At high elevations, this snow has been redistributed by strong southwest winds, loading lee features near ridges. The storm snow overlies a weak layer of feathery surface hoar and a hard melt-freeze crust on sun-exposed aspects, which has increased the reactivity of these slabs.
There are multiple weak layers buried around 80 to 200 cm deep, including two more surface hoar layers from December and weak faceted snow on a crust near the bottom of the snowpack from late November. It is possible that easier-to-trigger storm slab avalanches could step down to these deeper, persistent layers or that the weak layers could be human-triggered in areas where the snowpack is thin, rocky, or variable.
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Be alert to conditions that change with elevation and wind exposure.
- Storm slabs in motion may step down to deeply buried weak layers resulting in very large avalanches.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
Problems
Storm Slabs
Snowfall continues to accumulate and storm slabs remain reactive as slab depths increase and stiffen over a recently buried layer of surface hoar. Thicker slabs are found in wind-loaded terrain features, particularly near ridges. Conservative terrain selection is required to avoid this avalanche problem.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Recent very large avalanches released naturally on a persistent weak layer formed in late November. Additional loading from new snow and wind continues to test this layer. Shallower but more sensitive storm slabs carry the risk of triggering one of these deeper weak layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 5th, 2020 5:00PM
