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Avalanche Forecast

Archived

Nov 22nd, 2012–Nov 23rd, 2012

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

Northwest Coastal.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecaster's blog for further details on interpreting early season bulletins.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

Friday: Moderate to heavy snowfall starting Thursday afternoon is expected to bring 30-50cm of new snow, with the highest amounts concentrated in immediate coastal areas, before tapering off by the evening. Freezing levels around 600-800m and mountaintop winds are expected to be extreme southwesterlies during the height of the storm, but ease throughout the day. Saturday: Continued moderate snowfall with 15-25cm possible, again heaviest for immediate coastal areas. Freezing levels remaining in the 600-800m range and strong southwesterly mountaintop winds. Sunday: A mix of sun and clouds with isolated flurries and cooling as winds shift to northwesterlies.

Avalanche Summary

Explosives control last weekend produced a couple of 30cm deep size 1.5-2 storm slab avalanches. Natural avalanche activity followed by human-triggered activity generally occurs with every intense weather period, such as what's forecast for Thursday night and Friday.

Snowpack Summary

Total snowpack depth is probably at least a metre in most treeline areas and deeper but more variable in the alpine, while below treeline areas are probably still below threshold depths for avalanches. A recent profile at 1200m in the Shames area showed a predominately "right-side-up" 120cm deep snowpack with a thin layer of facets sitting on a crust 35cm off the ground. An Extended Column Test produced easy (10 taps)  results on this persistent weak layer , but the resistant fracture didn't propagate across the entire column. Check out the Skeena/Babine discussion forum for more information from the area.

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.