Regions
Kootenay Boundary.
Rising temperatures and solar input may push the danger higher than forecast. Conservative terrain choices are essential with this complex snowpack. Give cornices a wide and respectful berth.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Thursday
Weather Forecast
The high pressure ridge currently over the Province will be with us for a few more days. The next Pacific system is forecast to arrive on the coast late Friday afternoon and cross into the interior early Saturday morning. Freezing levels are forecast to rise quite high on Thursday afternoon and into Friday. Some models are showing freezing levels to 300 metres. Winds are forecast to be generally light and from the south.
Avalanche Summary
One report of a wind slab avalanche from yesterday, size 1.5 S-SW aspect at 1800 metres. Loose wet avalanches are being reported, starting in steep terrain on solar aspects.
Snowpack Summary
A considerable amount of snow fell during the previous week, with the eastern part of the region receiving the largest amount of snow.. Moderate to strong south west winds redistributed the surface snow into wind slabs. For the most part, these wind slabs should be bonding with the storm snow on all but high elevation terrain. The storm slab is now sitting on the melt-freeze crust that formed during the 2nd week of February and has been reported at various levels from 50 to 100cm throughout the region. This crust is widespread and may co-exist with surface hoar or weak facets. This reactive interface is a critical layer to watch in the region, and has been the active layer for some very large avalanches recently. Buried surface hoar from January is still being reported throughout the region and noted as a serious layer below 1800m. Surface hoar growing up to 8mm has been reported in the past few days. Sun crust may exist on solar aspects at the surface and has also been reported in the region 20cm below the surface. Daytime heating will help settle the snowpack but could also make for touchy conditions on south facing slopes in the afternoon.
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.
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.