Confidence
Fair - Freezing levels are uncertain for the entire period
Weather Forecast
On Wednesday the region sees the last drips and drabs of precipitation for a while. A strong ridge building from the western part of the province will bring dryer conditions for the forecast period. On Thursday ridgetop winds will be light from the NW; freezing levels may rise to 1200m and alpine temperatures steady near -5. Friday and Saturday the ridge of high pressure holds true with freezing levels potentially reaching 1800m.
Avalanche Summary
On Tuesday very little natural slab avalanche activity occurred. One report of a natural size 2 slab avalanche occurred on a cutbank @ 800m, on a 35 degree North aspect. Reports indicated natural sluffing from steep rocky features, and skier triggered sluffing within the recent storm snow, up to size 1.5. What did catch my eye was two separate reports of size 3 slab avalanches. The reports came in from Southern parts of the region. The actual avalanches were unobserved, but details revealed crown sizes 150cms deep, which could possibly be the mid-January SH/FC layer. One slide initiated from a steep gully feature and triggered the slope below at 1700m. The other slide reportedly took out mature timber. These both occurred on NE-E aspects. Cornice fall may increase later in the week due to warming temperatures, which may provide large enough triggers on slopes below.
Snowpack Summary
Storm slabs up to 60cms thick developed over the weekend at all elevations. Wind slabs have formed on North through East slopes in the alpine and at treeline. Buried below the storm snow seems to be a fairly settled mid-pack, with a couple lingering layers.We continue to monitor the January 13th surface hoar/facet layer, and the January 25thlayer. Recent snowpack field tests have shown generally moderate results, including resistant planar shears. I suspect the snowpack is settling out, and generally bonding above these. With warming temperatures forecast we may start to see these mid-January layers become reactive, producing large avalanches. Recently there have been two reports of large avalanches (size 3) that have crown depths of 150cms. I suspect these may have occurred on this layer but have no solid evidence to back it. The average snowpack depth at 1700m is 2-3 m.
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.