Lots of uncertainty in the snowfall forecast for Tuesday and Wednesday. If it's dumping snow, consider the avalanche danger high.
Confidence
Low - Forecast snowfall amounts are uncertain
Weather Forecast
TUESDAY: Cloudy with snow. Snowfall amounts are hard to call. One senior meteorologist is predicting a 'Fernie effect', which could bring up to 40 cm of dry snow to parts of the South Rockies in short order late in the day. Light to moderate winds. Alpine temperature near -6.WEDNESDAY: Moderate westerly winds. Light snow. Alpine temperature near -15.THURSDAY: Moderate to strong winds. Light snow. Alpine temperature near -15.
Avalanche Summary
A timber sledder triggered and was caught in a small avalanche on a road cut on Sunday. It occurred a little below treeline, south of the Crowsnest. Avalanche conditions seem especially touchy in this type of terrain right now. Give extra thought to the presence of terrain traps like roads, gullies and trees. Even a small avalanche can have increased consequences in combination with a terrain trap.Reports over the last few days have been limited, but recent whumpfing and a bunch of persistent slabs last week are all evidence of this problem. With warming or increased load by snow and/or wind-loading, persistent slab activity is likely to increase again.
Snowpack Summary
The snowpack is variable across the region, but the two key concerns are touchy persistent slabs and wind slabs. Wind slabs may exist lower on the slope than normal, due to recent extreme south-west winds. In some parts of the region, windward alpine slopes are scoured; and variable wind slabs are found at treeline and alpine elevations. A touchy weak layer from mid-December (predominantly feathery surface hoar crystals and/or a sun crust) is found at treeline and below. Slabs are failing very easily on this layer with the weight of a person or machine.Deeper in the snowpack, an early season rain crust and sugary facets make up the picture. Overall snowpack depths are variable across the region. It's generally shallower in the east.
Problems
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.
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.