Convective flurries and moderate southwest winds may form fresh wind slabs on lee features at Treeline and above.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
TUESDAY: Cloudy with flurries, 5-10 mm rain/snow. Moderate southwesterly ridgetop winds. Freezing level around 1900m.WEDNESDAY: Mostly cloudy. Moderate to strong southwesterly ridgetop winds. Freezing level around 2000 m.THURSDAY: Mix of sun and cloud. Light southeasterly ridgetop winds. Freezing level around 2000m.NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.
Avalanche Summary
Several loose wet avalanches to size 2 were reported on a variety of aspects in this region on Sunday. Falling cornices triggering large avalanches is currently our primary concern.
Snowpack Summary
Triggering large avalanches on facets near the bottom of the snowpack is currently our primary concern. On high north facing terrain, which is currently where the best skiing can be found, the problem is the possibility that if a large cornice falls on a steep slope, it will trigger this layer. On solar aspects, the problem is small loose wet or wind slab avalanches stepping down to this layer or skier triggering the layer by hitting a shallow spot in a large, steep, and rocky alpine face. Additionally, convective flurries and moderate winds may form fresh wind slabs on lee features at Treeline and above on Tuesday. Fresh snow combined with warm temperatures will increase the likelihood of small loose wet avalanches on all aspects at Treeline and below.
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.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.