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Avalanche Forecast

Archived

Dec 17th, 2019–Dec 18th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Snow in the forecast for the end of the week! Until then, triggering an avalanche is most likely in wind affected terrain and steep, rocky slopes.

Confidence

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

Weather Forecast

Tuesday Night: Cloudy with clear breaks. Alpine temperature -8 C. Southwest-west wind 20-35 km/hr.

Wednesday: Mix of sun and cloud. Alpine temperature -6 C. Southwest wind 25-35 km/hr.

Thursday: Cloudy with isolated flurries, trace to 10 cm. Alpine temperature -8. Southwest wind 25-45 km/hr.

Friday: Snow, 15-30 cm. Alpine temperature -2C. Southwest wind 20-40 gusting to 65 km/hr.

Avalanche Summary

Explosives testing was able to trigger a handful of small (size 1) slab avalanches on Tuesday from steep alpine terrain. 

Last 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.

Snowpack Summary

Wind has redistributed loose snow, and formed wind slabs in alpine 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 around 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.