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Avalanche Forecast

Archived

Feb 11th, 2019–Feb 12th, 2019

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

Regions

Purcells.

Wind slabs may be touchy on all aspects in exposed terrain. There has also been recent large human-triggered avalanches and other signs of instability on buried surface hoar layers. See our Forecaster Blog for more info here.

Confidence

High -

Weather Forecast

MONDAY NIGHT: Cloudy with intermittent snowfall, accumulation 1 to 3 cm, moderate southwest wind.TUESDAY: Cloudy with light snowfall, accumulation trace to 10 cm with the most in the south of the region, moderate to strong southwest wind, alpine temperature -15 C.WEDNESDAY: Cloudy with light snowfall and afternoon clearing, accumulation 1 to 3 cm, light northwest wind, alpine temperature -14 C.THURSDAY: Increasing clouds over the day, light east wind, alpine temperature -10 C.

Avalanche Summary

A few large wind slab avalanches were observed in the region on Sunday, generally in alpine terrain and up to 60 cm deep. Otherwise, cornices were reactive to explosive control.The January persistent weak layers described in the Snowpack Summary continue to be reactive to human triggers. The most recent activity was on Friday, as skiers triggered large avalanches on east and southeast slopes between 1900 and 2300 m. Check out the MIN reports here, here and here for examples of these weaknesses.

Snowpack Summary

Recent strong winds from all directions have affected the snow surface at all elevation bands. Expect to find wind slabs in terrain depressions, such as adjacent to ridges, and otherwise wind affected snow on all aspects.Beneath this lies two weak layers of surface hoar that were buried at the end of January and mid-January. These layers are around 30 to 60 cm deep. The mid-January layer may be associated with a melt-freeze crust on southerly aspects. These layers are most prominent at treeline and below treeline elevations.The base of the snowpack is composed of weak and sugary faceted grains that overly a melt-freeze crust. This weak layer has produced large and destructive avalanches that are sporadic in nature and very difficult to predict. It is most likely to be triggered from areas where the snowpack is shallow and weak. Rocky alpine bowls, ridge crests, and rocky outcroppings are some examples of terrain features to be wary of. See the Forecaster Blog here for more info on this problem.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.