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Avalanche Forecast

Archived

Feb 13th, 2019–Feb 14th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Purcells.

Avalanche danger south of Cranbrook and south is CONSIDERABLE. Up to 40 cm of new snow fell on Tuesday in the most southern part of the region.

Confidence

Moderate -

Weather Forecast

WEDNESDAY Night: Clear periods, light southeast wind, alpine temperature -15 C.THURSDAY: Mix of sun and cloud, light to moderate southeast wind, alpine temperature -8 C.FRIDAY: Flurries, accumulation 5-10 cm , light to moderate southwest wind, alpine temperature -7 CSATURDAY: Flurries, accumulation 10-15 cm, moderate west wind, alpine temperature -8 C

Avalanche Summary

Recent activity on Monday and Tuesday includes a few naturally triggered wind slab avalanches in the alpine to size 1.5. A few large wind slab avalanches were observed in the region on Sunday, generally in alpine terrain and up to 60 cm deep.

Snowpack Summary

In much of the region 5-10 cm of recent snow sits above wind-affected snow and/or sugary facets. In the far south of the region (south of Cranbrook) 30-40 cm of new snow that fell Tuesday also sits above wind-affected snow or sugary facets. 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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.