Avalanche Forecast

Archived

Mar 12th, 2022–Mar 13th, 2022

Alpine

Natural avalanches unlikely, human triggered possible.

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 possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Sea To Sky.

Watch for pockets of wind slab at upper elevations. Don't forget about a buried weak layer that remains triggerable.

Confidence

Moderate -

Weather Forecast

Saturday night: Cloudy with snowfall, accumulation around 5-10 cm, 20-30 km/h south wind, alpine temperature -6 C. Freezing level 1000 m.

Sunday: Cloudy with scattered flurries, 10-20 km/h southwest wind, alpine temperature -5 C. Freezing level 1500 m.

Monday: Cloudy with snowfall, accumulation 15-30 cm, 40-60 km/h southwest wind, alpine temperature -5 C. Freezing level 1500 m.

Tuesday: Cloudy with snowfall, accumulation 20-40 cm, 30-50 km/h southwest wind, alpine temperature -5 C. Freezing level 1400 m.

Avalanche Summary

On Saturday, a few skier controlled size 1 loose dry and soft wind slab avalanches were reported.

Persistent slab activity has dwindled since last week. The most recent activity was on Tuesday when two avalanches were triggered by riders on northeast aspects at treeline and alpine elevations, similar to the trend of previous avalanches. It remains possible that humans could trigger this layer, where it exists.

Snowpack Summary

Small amounts of new snow and southwest wind have likely formed small wind slabs in lee terrain features. The snow accumulates over a thin layer of variably wind affected, faceted snow or surface hoar that overlies a hard melt-freeze crust found on all aspects below around 1500 m and on sun-exposed slopes into the alpine. The snow sits on previously wind-affected and faceted snow on shaded slopes above 1500 m.

Around 40 to 80 cm deep, a weak layer of sugary faceted grains may be found above a melt-freeze crust that formed in February. This layer has produced about one or two human-triggered avalanches per day over the past week. Activity has been most prevalent on north to northeast aspects between 1600 m and 2100 m. Check out this forecaster blog for more info.

There are no deeper concerns at this time.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Closely monitor how the new snow is bonding to the old surface.
Be aware of the potential for large avalanches due to the presence of a persistent slab.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.