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Avalanche Forecast

Archived

Apr 20th, 2014–Apr 21st, 2014

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

Avalanche danger can rise quickly with afternoon warming and solar radiation. Be aware of changing conditions and overhead hazards.For more insight into spring danger ratings, check out this Blog Post.

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Light precipitation is expected to continue for Monday and Tuesday. A weak ridge of high pressure should bring at least partially sunny conditions for Wednesday. There is some model uncertainty and a possibility that the ridge could build over the south coast on Tuesday.Monday: Precipitation 2-4mm, freezing level am: 1200m pm: 1700m, ridgetop wind: light S-SWMon. Night/Tuesday: Light precipitation 3-6mm, freezing level am: 1200m pm: 1500m, ridgetop wind: light SWWednesday: A mix of sun and cloud, convective flurries possible, freezing level am: 1000m pm: 1600m, ridgetop wind: light SW

Avalanche Summary

On Saturday, explosive control released a cornice which triggered a size 2.5 slab that released to ground. A natural size 1 cornice and isolated size 1 soft slabs from leeward features were also reported.On Friday, several storm slab avalanches up to size 2 were reported. These were triggered both by skiers and explosives and released down 10-50cm. Natural soft slab avalanches up to size 2.5 were also reported in the region releasing in the storm down 20-35cm with good slab propagation. Natural sluffing from steep features to size 1.5 was also reported.

Snowpack Summary

A highly variable spring snowpack exists across the region and conditions can change rapidly throughout the day. At lower elevations below-treeline, the snowpack is isothermal and melting rapidly. At mid elevations, between roughly 1500 and 2000m (and higher on sunny slopes), the snowpack is undergoing daily melt-freeze cycles. In the mornings, a refrozen surface generally means good stability. In the afternoon when the surface melts, the stability can deteriorate quickly, especially on sunny slopes. The recent storm has produced dry snow in the alpine resulting in the formation of storm slabs and wind slabs which sit on an old crust. The stability of these slabs has generally been improving but on the first really sunny day, stability is expected to deteriorate rapidly and natural avalanche activity is likely, especially on sunny slopes. Large cornices remain a concern and are expected to become reactive during periods of solar warming. The early-Feb facet/crust layer (down ~2m) and a weak basal layer are both dormant but remain a concern during periods of intense warming, especially in thinner snowpack areas, when large spring avalanches may step down to these layers.

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.

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.

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.