Weather Forecast
Synopsis: A weak weather system will bring more cloud and light precipitation to the South Coast for Tuesday and Wednesday. A ridge of high pressure should build in for Thursday and Friday bringing mainly sunny skies. Tuesday: Increasing cloud with light precipitation (2-4 cm). The freezing level will rise to around 1100 m during the day. Winds are light from the southeast. Wednesday: Cloudy with light precipitation (4-8 cm). The freezing level is around 1200 m and winds are light from the southeast. Thursday: A mix of sun and cloud. The freezing level is steady around 1200 m.
Avalanche Summary
A widespread natural avalanche cycle (with avalanches from size 2-4) occurred on Friday/Saturday in response to intense storm-loading. Numerous large, deep fracture lines can be seen from the Sea-to-Sky corridor. Many of these failed low in the start zone, leaving hangfire (unreleased areas of the slope). Natural avalanche activity slowed down on Sunday but explosive control continued to produce results up to size 3 and there were a couple reports of skier triggered avalanches up to size 2, primarily from north through east aspects in the alpine.
Snowpack Summary
Strong NW winds redistributed storm snow onto south and east aspects on Saturday. This reverse loading may have left wind slabs in unexpected locations.The recent storm delivered well over 100 mm of precipitation, which fell with warming temperatures, dropping rain below about 1500-1900 m, depending on location. Strong southerly winds during the storm created wind slabs on lee terrain. Numerous weaknesses developed within the storm snow. A weakness of surface hoar and/or a crust exists within the upper snowpack (now 1-2 m deep), which has been reactive over the last week, creating very large avalanches. Direct sunshine may trigger some further shedding of storm snow on Monday. The lower snowpack is well settled.
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.