New snow with strong winds will form touchy wind slabs at upper elevations. Use conservative terrain selection and avoid wind-loaded features.Check out the new video by the South Rockies Field Team in our blog section: www.avalanche.ca/blogs
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A storm system will bring light precipitation to the region on Saturday. Models are currently forecasting 3-6mm. Freezing levels will start at over 2000m but should fall to around 1500m by the end of the day meaning rain may switch to snow at many elevations. Alpine winds are expected to be strong from the SW. On Sunday, a weak ridge of high pressure should build over the interior resulting in a mix of sun and cloud. Freezing levels on Sunday are forecast to reach around 2000m and alpine winds should be light. Another storm system may reach the region on Monday bringing light precipitation.
Avalanche Summary
A widespread natural avalanche cycle to size 2.5 occurred on Monday during the storm. These were primarily storm slab avalanches but several stepped down to deeper persistent weak layers or to the ground in steep unskiable terrain. At lower elevations, loose wet avalanches up to size 2.5 were reported as well as isolated wet slabs. Natural avalanches quickly tapered off during the storm but touchy conditions existed through the week. Winds increased on Thursday and wind slab formation has been ongoing since. With strong winds and precipitation continuing on Saturday, wind slabs will continue to build and are expected to be touchy. Loose wet avalanches are a problem at lower elevations where it is raining.
Snowpack Summary
A moist or wet snow surface is expected on all aspects to around treeline and on sun-exposed slopes into the alpine. Dry snow can likely still be found on sheltered high elevation slopes. Ongoing strong SW winds are redistributing the surface snow in exposed high elevation terrain. New wind slabs are expected to be building in leeward features and will be enhanced with the upcoming snowfall. A weak rain crust from last weekend is down 30-50cm and has a good bond with snow above. There are a couple older persistent weak layers in the midpack that are still intact and have the potential to wake-up with substantial warming or heavy loading. Cornices may become fragile with afternoon warming.
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 Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.