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Avalanche Forecast

Archived

Nov 26th, 2019–Nov 27th, 2019

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

Regions

Northwest Coastal.

Strong wind will maintain dangerous conditions in alpine terrain on Wednesday. Stick to sheltered terrain and be aware that the recent snow may need more time to stabilize.

Confidence

Moderate - Uncertainty is due to the extreme variability of wind effect on the snowpack.

Weather Forecast

TUESDAY NIGHT: Clearing skies, 50-70 km/h outflow winds from the northeast, alpine temperatures drop to -12 C.

WEDNESDAY: Sunny, 50 km/h outflow winds from the northeast, alpine temperatures around -10 C.

THURSDAY: Sunny, light wind from the northeast, alpine temperatures around -8 C.

FRIDAY: Sunny, light wind from the northeast, alpine temperatures around -5 C.

Avalanche Summary

While the storms over the weekend likely caused a widespread cycle of natural avalanches, there are few observations at this time of year. Reports from northern parts of the region confirm there were some natural storm slab and wind slab avalanches over the weekend. Looking forward, clearing weather is likely to make travel in the mountains a more inviting prospect, however this is a time to be on high alert in any areas where new snow buried a smooth surface and where winds have formed new slabs. Concern is reduced in areas where the new snow hasn't yet overcome the depth of ground roughness.

Snowpack Summary

Strong wind from the northeast will form new wind slabs on west and south facing slopes at higher elevations. The succession of storms over the weekend delivered much more snow towards the coast than inland (150 mm of precipitation at Shames and only 36 mm at Rosswood). Recent observations from Shames suggest this resulted in about 30 cm of snow at 750 m, 100 cm of snow at 1200 m, and likely over a metre of snow in the high alpine (see this MIN report). Beyond the sheer quantity of new snow (easily tripling the previous snowpack depth), the bond between the new snow and the old crust will remain in question for a few days. Forecast cool temperatures are expected to contribute to a slow bonding process.

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.