Avalanche Forecast

Archived

Mar 29th, 2021–Mar 30th, 2021

Alpine

Natural avalanches possible, human triggered probable.

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, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

Storm slabs at higher elevations may be reactive on Tuesday, especially in wind-loaded areas.

If the sun pokes through the clouds it can quickly initiate natural avalanches and weaken cornices.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

A ridge of high pressure will dominate for the next couple of days bringing cooler and dryer conditions.

Tuesday: Mainly cloudy. Ridgetop wind moderate from the northwest. Alpine temperatures near -2 and freezing levels 1000 m.

Wednesday/ Thursday: Mix of sun and cloud with some snow expected Thursday up to 5 cm. Ridgetop wind moderate from the southwest. Alpine temperatures near +1 and freezing levels 2000 m.

Avalanche Summary

On Sunday, natural storm slab avalanches up to size 2 were reported and numerous size 1.5 slabs were easily triggered by skiers and riders from steep slopes where the new snow sits above a crust.

The likelihood of triggering avalanches will decrease somewhat in the wake of Sunday's storm, however, human triggering remains likely, especially in wind loaded areas at upper elevations. With so much new snow, even short periods of direct sun can trigger natural avalanches. Cornices are large and should be given a wide berth, especially when the sun comes out.

Snowpack Summary

20-40 cm of new snow fell throughout the region since Saturday night. This sits above a widespread melt-freeze crust, with the exception of high north-facing terrain. It may also be sitting on small surface hoar crystals reported on north and east aspects in the alpine. This recent precipitation likely fell as rain in many areas below treeline. The snow surface has likely frozen into a crust at lower elevations.

Cornices along ridgelines are large, and the likelihood of them failing will increase when the sun comes out.

Terrain and Travel

Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Brief periods of sun could quickly initiate natural avalanche activity.
Be aware of highly variable recent wind loading patterns.
Cornices become weak with daytime heating or solar exposure.

Problems

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.