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Avalanche Forecast

Archived

Feb 25th, 2017–Feb 26th, 2017

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

South Coast Inland.

Recent snowfall has resupplied wind slabs in the south of the region. Recent persistent slab activity should rein in terrain selection in the north.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Saturday night: Cloudy with scattered flurries bringing up to 5 cm of new snow. Winds moderate from the west. Sunday: A mix of sun and cloud. Winds light to moderate from the northeast. Freezing level to 400 metres with alpine temperatures of -10. Closer to 800 metres and -5 in the south of the region. Monday: A mix of sun and cloud. Winds light to moderate from the west. Freezing level to 200 metres with alpine temperatures of -11. Closer to 500 metres and -6 in the south. Tuesday: Mainly cloudy with isolated flurries bringing a trace to 5 cm of new snow, beginning in the evening. Winds light to moderate from the west. Freezing level to around 400 metres with alpine temperatures around -8.

Avalanche Summary

No new avalanches were reported on Friday. A social media report from Thursday showed an impressive persistent slab release to approximately Size 3 in the Hurley area. The slab was triggered with a cornice cut on an apparently northeast aspect, though it should be noted that the cornice was not large. See the video here. The above report has combined with the Size 3 persistent slab avalanche observed up the Hurley on Friday to suggest the possibility of an emerging pattern of persistent slab activity in that part of the region. The failure planes of each slide remain uncertain, but the early February surface hoar layer was suspected in Friday's occurrence.Two MIN reports from Thursday describe three skier-triggered Size 2 wind slab avalanches near Mt. Matier, serving as a reminder that our wind slab problem hasn't disappeared yet. While wind slabs remain a concern throughout the region, a low-probability/high consequence avalanche problem should be driving a more cautious approach to backcountry travel in the north of the region.

Snowpack Summary

Convective flurries have delivered a spotty 5-20 cm of new snow to the region over the past couple of days, with the greatest accumulations occurring in the south. Below the new snow, the previous snow surface consisted of surface facets and surface hoar to 6 mm, as well as sun crust on steep solar aspects. Beneath the new snow interface, 10-30 cm of recent storm snow overlies the widespread mid-February crust layer at higher elevations. Reports suggest this snow is well bonded to the crust but has been undergoing faceting as a result of recent cold temperatures. In the north of the region, a facet/surface hoar layer from early February, down 60-100 cm, remains reactive in snowpack tests and is suspected as the failure plane in at least one of two recent large persistent slab avalanches in the Hurley area. In the south of the region, the mid and lower snowpack are well settled and strong.

Problems

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.

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.