Regions
South Coast Inland.
Ridgetop winds are strong from the southwest, building reactive wind slabs at upper elevations. Rising freezing levels will weaken the snow surface and increase the likelihood of triggering avalanches.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Wednesday: Mostly cloudy with scattered flurries. New snow 5-10 cm. Ridgetop wind strong from the southwest and freezing levels rising to 1800 m. Thursday: Mix of sun and cloud. New snow up to 5 cm. Ridgetop wind strong from the southwest and freezing levels 1200 m. Friday: Yet another blast of winter up high! Heavy snow. Up to 20 cm in the North and up to 40 cm in the South. Ridgetop winds strong-extreme from the southwest with freezing levels near 1500 m.
Avalanche Summary
On Monday, a small natural avalanche cycle was observed from southeast aspects around 2300m. Widespread whumphing was observed in a drainage in the north of the region, which was suspected to have been on the late-March weak layer described in the Snowpack Summary. Expect the avalanche hazard to rise through the forecast period with new snow and wind.
Snowpack Summary
Up to 10 cm of new snow overlies moist snow surfaces. At higher elevations, this overlies slabs formed from last weekends snow that fell with strong southwesterly winds. On ridges, cornices are reported to be large and fragile. At low elevations below treeline, recent rain has created moist or wet snow conditions.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.The mid and lower snowpack are well-settled and strong.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.