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Avalanche Forecast

Archived

Dec 16th, 2019–Dec 17th, 2019

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

Lizard-Flathead.

A stable weather pattern is forecast for the next few days with flurries at the end of the week.

Confidence

Moderate - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

Monday Night: Cloudy with clear periods and isolated flurries, trace to 5 cm. Alpine temperature -10 C. Southwest wind 25-45 km/hr.

Tuesday: Partly cloudy, partly sunny. Alpine temperature -6 C. Southwest wind 30-45 km/hr.

Wednesday: Mix of sun and cloud. Alpine temperature -6 C. Southwest wind 25-40 km/hr.

Thursday: Flurries, up to 10 cm. Alpine temperature -5. Southwest wind 15-35 km/hr.

Avalanche Summary

On Saturday, 2 large (size 2) natural storm slab avalanches were reported initiating from steep north-north east aspects in the alpine. Around Fernie, the new snow was reactive to skier tracks.

Avalanche activity late last week was primarily limited to small wind slab avalanches (size 1) triggered with explosives. On Thursday there was a report of a size 2.5 storm slab avalanche on a northeast aspect in the alpine, which scoured down to a crust near the base of the snowpack.

Snowpack Summary

Wind has redistributed loose snow, and formed wind slabs in exposed terrain and around ridge features. In sheltered areas 30-40 cm of snow from last weekend is gradually settling. 

Crust layers from November and October can be found 40-100 cm below the surface. These layers produced large avalanches with explosive triggers last weekend (Dec 13-14), but since then have appeared to gain strength. Large avalanches on these layers may still be possible to trigger in steep rocky terrain. 

Snowpack depths range between 50-130 cm at higher elevations and taper rapidly below treeline. Check out this MIN reporting conditions on Sunday at Harvey Pass.

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.