Regions
Northwest Inland.
Weather Forecast
Synopsis: A windy pacific storm is heading your way Saturday, clearing out Sunday.Saturday: 5 to 10 mm additional precipitation bringing storm totals in the range of 10 to 25 mm of water (somewhere around 15 to 30 cm of snow); Strong SW winds easing and veering W late in the day; freezing level below 500 m with alpine temperatures around -5Sunday & Monday: drier with less than 5 cm of snow; cooler temperatures with freezing level at the valley bottom and around -8 in the alpine; light SW wind Saturday becoming light E wind on Monday.
Avalanche Summary
On Wednesday, a snowmobile triggered a hard wind slab at Sinclair. It failed on the November crust/facet layer 30 cm above the ground. Evidence of a recent natural cycle was also reported. This deep crust/facet layer has been the failure plane for a number of large avalanches further to the west and was suspected to have failed at the Hankin-Evelyn area last weekend. Unfortunately, this weakness is unlikely to heal very quickly, so further deep avalanches are possible, especially as snow and wind-loading continue to stress the snowpack over the next few days.
Snowpack Summary
Short-lived storm snow instabilities are likely to develop on steeper terrain as new snow continues to accumulate. But more importantly, forecast wind is sure to concentrate it and build deeper touchy windslabs; they may form lower down on slopes than typically expected. Older hidden windslabs from previous winds may still linger; remember that those winds blew from many directions so just about any exposed slope could harbour one. Spotty surface hoar is also buried in the upper snowpack, particularly in sheltered treeline areas. Of key concern is a November facet/crust layer which can be found near the base of the snowpack. This layer, which is widespread, can be triggered from thin-spot trigger points, or with a heavy load, such as storm slabs stepping down, cornice fall or a snowmobile. It has the potential for very large, destructive avalanches and demands respect. A rain crust is buried in the upper snowpack at low elevations. In general the snowpack is highly variable in depth due to windy conditions this season.
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.
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.