Regions
Northwest Inland.
Recently formed wind slabs are expected to remain reactive to human triggering on Wednesday. Use extra caution as you transition into wind affected terrain and watch for signs of recent wind loading in leeward terrain features.
Weather Forecast
A ridge of high pressure is expected to keep the region cold and dry for a couple more days before the next storm system hits the coast on Friday. Wednesday is expected to be sunny with light to moderate outflow winds and treeline temperatures around -15C. A temperature inversion is expected and temperatures will likely be colder at valley bottom than at higher elevations. A mix of sun and cloud is forecast for Thursday with light outflow wind and treeline temperatures around -15C. The storm system is currently forecast to arrive midday Friday but models are currently only showing 2-4 cm of snowfall by the end of the day.
Avalanche Summary
No new avalanches were reported on Monday. On Sunday, a skier remotely triggered a size 2 wind slab avalanche on a southwest aspect at 1200 m elevation. The slab was 60 cm thick and was triggered from 10 m away. On Saturday, a natural size 2 wind slab avalanche was reported on a north aspect at 1600 m elevation with a slab thickness of 30 cm. On Friday, a natural size 2.5 deep persistent slab was observed in the far north of the region on a southeast aspect at 1800 m elevation which released on the ground.On Wednesday, expect recently formed wind slabs to remain reactive to human triggering. Ongoing outflow winds may continue to add additional load to these wind slabs in places where there is still snow available to be redistributed. A basal weakness continues to create a low probability/high consequence problem for the region and very large avalanches remain possible, especially in shallow snowpack areas.
Snowpack Summary
Widespread wind affected surfaces are being reported in exposed terrain including scoured surfaces, sastrugi, and hard wind slabs. In areas sheltered from the wind, the surface snow is reported to be faceting and surface hoar is developing. Below around 1400 m elevation, a rain crust can be found near the surface of the snowpack. Deeper in the snowpack, several buried surface hoar layers can be found between 30-70 cm deep. Recent reports suggest these layers have generally stabilized but isolated weaknesses may still exist, especially where buried surface hoar is still intact. A generally stiff mid pack sits above weak sugary snow near the ground. This basal weakness woke up during the last storm and produced numerous large avalanches which released on the ground. The layer is dormant for the time being but is expected to wake up with warming or heavy loading, or a smaller avalanche could step down.
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.