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Avalanche Forecast

Archived

Apr 20th, 2018–Apr 21st, 2018

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

Regions

Sea To Sky.

Forecast snowfall amounts are extremely variable throughout the region. Pay close attention to how much snow falls in your riding area and be prepared to back-off to simple terrain.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

Friday night and Saturday: 15-30cm of new snow / Strong to extreme southwest winds / Freezing level at 1300mSunday: Clear skies / Light and variable winds / Freezing level at 1900mMonday: Clear skies / Light and variable winds / Freezing level at 2400m

Avalanche Summary

On Wednesday explosives control work in the ranges west of the Pemberton Icefield produced size 3 persistent slab avalanches that are suspected to have failed on the late March weak layer. Observations of older, natural size 3-3.5 avalanches in the area where also attributed to this persistent weak layer. Older natural size 3-3.5 avalanches were also observed at 1800-2100 m in the McBride range. I would expect intermittent persistent slab activity with warming and solar radiation forecast for Sunday and Monday. In the short term, new snow and wind will promote new wind slab activity on Saturday.

Snowpack Summary

New snow and wind on Saturday are expected to form fresh wind slabs in upper elevation lee terrain. The new snow is expected to overlie settled storm snow on shaded aspects above 2000m and a melt-freeze crust in most other areas.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm below the surface. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is most likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. Professionals are treating this layer very cautiously and avoiding steep, unsupported terrain. Read Conditions report here.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.