Regions
Northwest Inland.
The Avalanche Danger may change quickly in the spring. Even brief periods of sun or rain can trigger pushy loose wet avalanches or promote destructive cornice falls.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
On Wednesday expect 5-10cm of new snow with strong southwest ridgetop winds while continued light snowfall (5-8cm) and decreased winds are forecast for Thursday. Clearing skies are forecast for Friday as a dry ridge of high pressure develops over the province. Freezing levels should hover between 1100 and 1200m for the forecast period.
Avalanche Summary
In recent days a natural cornice fall triggered a size 3 slab avalanche in the southwest corner of the region. The avalanche occurred on an east aspect in high alpine terrain and stepped down to a few persistent weak layers from January and December. This avalanche demonstrates how a cornice fall can trigger layers that may otherwise be difficult to trigger. On Monday loose wet avalanches to size 2 were reported to have occurred in steep terrain on a variety of aspects. They failed in response to periods of solar warming or rain. New wind slab activity is expected in response to new snow and strong winds on Wednesday.
Snowpack Summary
In some areas, a dusting of new snow overlies wind slabs in exposed high elevation terrain and settled dry (and faceting) powder on shaded and sheltered slopes. Spring conditions have continued to develop. With that, lower elevation and sun-exposed slopes will likely appear moist or refrozen. A layer of surface hoar from early March can be found down 50-70cm but only seems to be a problem for the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February which can be found down about 1m or more. These layers have been dormant for a couple weeks but could wake up with substantial warming or a heavy trigger (like a cornice fall). Basal facets exist in most areas and have recently become reactive in the north of the region
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.
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.