Regions
Northwest Inland.
Avalanche Danger is expected to quickly drop with cooling over the weekend but there may still be lingering problems. Give the snowpack time to cool down before venturing into complex terrain.
Weather Forecast
Increased cloud will develop throughout Sunday with 5-15cm of new snow expected between Sunday night and Monday morning. Generally overcast skies and light flurries are expected on Monday although an intense frontal system will bring moderate to locally heavy snowfall (~ 30cm) to the region on Tuesday. Ridgetop winds will be moderate from the southwest on Sunday night, and then spike to extreme with Tuesday's storm. Freezing levels should sit at about 1400m for the forecast period.
Avalanche Summary
In recent days, loose wet avalanches up to size 2.5 were reported throughout the region. Numerous slabs up to size 2.5 were reported on solar aspects in the far north of the region. Some of these releases were over 2m deep releasing on old weak layers. In the south, a natural icefall triggered a size 2.5 slab avalanche, while a full depth slab avalanche was reported on Hudson Bay Mtn. Conditions are expected to improve quickly when the temperatures drop on Saturday but there has been so much heat added to the snowpack over the last few days that some of the deep persistent weak layers may remain reactive for a few days. Once the snow surface develops a widespread supportive crust layer, it will become unlikely to trigger any deep weaknesses. Lingering cornices may remain reactive to human-triggering until there has been substantial cooling.
Snowpack Summary
Over the last couple days, the snow surface has been developing a weak crust overnight which has been quickly breaking down in the morning due to the warm temperatures. With the freezing levels dropping substantially Friday overnight, a more substantial crust has likely formed and is not expected to fully break down on Saturday at higher elevations. If the crust remains supportive, it is expected to cap any deeper weaknesses. The warm temperatures and sun over the last week have woken up deeply buried weak layers within the snowpack. This includes a weak crust/surface hoar layer which was buried down 20-30cm in the north of the region, a widespread crust/facet layer buried in early February down up to 1m, a lingering surface hoar layer from January down around a meter, and weak basal facets at the bottom of the snowpack. These old weak layers may still have isolated potential to produce large avalanches over the weekend, especially with a large trigger such as a cornice fall. Once the snowpack has seen substantial cooling, these layers are expected become inactive.
Problems
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.
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.