Regions
Northwest Inland.
The hazard may go higher than expected if precipitation and winds are higher forecast. Use great caution around cornice features.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
The Northwest Inland will see light precipitation through the weekend, with clearing skies late Sunday in advance of a ridge of high pressure that will dominate the weather pattern for most of next week. TODAY: Freezing level to around 1200 m, trace of snow, light to moderate southeast winds. SUNDAY: Freezing level dropping to 700 m overnight, then rising to 1300 m during the day. Possible 5 cm of snow, light winds from the southwest. MONDAY: Freezing level dropping to 700 m overnight, then beginning to rise to 1500 m by midday. No precipitation in the forecast. TUESDAY: Freezing level starts at 700 m early Tuesday morning, then begins to rise reaching 2700 m by early Tuesday evening. Light to moderate winds mostly from the west, no precipitation in the forecast.
Avalanche Summary
Loose wet avalanches on solar aspects below treeline are in the news from yesterday. It is spring, after all ! Some sluffing in steep terrain and of course, cornice failures are on everybody's minds. Natural cornice failures have been recently reported triggering avalanches up to size 2.
Snowpack Summary
At treeline and above small wind slabs overlie a variety of surfaces include crust on solar aspects above 1300 m, moist or refrozen snow on all aspects below 1300 m, and settled wind slabs in exposed high elevation terrain. There is a surface hoar layer formed in early March that may still be found down 50 to 70 cm. It is still being mentioned by operators in the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February that are now down about 1 meter or more. These layers are generally dormant but might wake up with increased warming or a heavy trigger (like a cornice fall). Basal facets exist in most areas and have been shown to be 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.