Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Regions
South Coast Inland.
The calm before the storm!Watch for wind slabs in the immediate lee side of ridgelines. They may be reactive to human triggers.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Thursday: Cloudy with some sunny periods. New snow up to 5 cm and strong southwest winds at ridgetop. Freezing level 1300m.Friday: Stormy. New snow 15-25 cm through the day. Ridgetop winds strong from the South. Freezing levels 1400 m. Saturday: The storm continues, bringing another 15-20 cm. Ridgetop winds strong from the southwest. Freezing levels 1500 m. Less snow amounts expected in the Northern areas of the forecast region.
Avalanche Summary
On Monday, a MIN report from the Duffy Lake area showed a skier accidental size 2 storm slab from a north aspect at 2700 m. Please check out the report here. No new observations on Tuesday or Wednesday, however, alpine observations seemed limited due to the weather. 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.