Avalanche Forecast

Issued: Feb 13th, 2019 4:36PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs, Persistent Slabs and Deep Persistent Slabs.

mbender, Avalanche Canada

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.

Summary

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

A storm slab problem is isolated to areas south of Cranbrook where up to 40 cm of new snow fell on Tuesday. Lingering windslabs at tree line and in the alpine may still be reactive in areas further north.

Storm slabs may step down to deeper layers and result in large avalanches.Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Two weak layers of surface hoar crystals are buried between 30 and 60 cm in the snowpack. The layers are most prominent around treeline and below treeline elevations.

Avoid steep, open and/or sparsely treed slopes at and below treeline.Be aware of the potential for wide propagation.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Deep Persistent Slabs

Particularly in thin snowpack areas, the base of the snowpack is composed of weak faceted grains and a crust. This layer has produced sporadic but very large avalanches. The probability of triggering this layer is low, but the consequences very high.

Minimize overhead exposure; avalanches triggered by cornice fall may be large and destructive.Use caution on alpine slopes, especially around thin areas that may propagate to deep instabilities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 3.5

Valid until: Feb 14th, 2019 2:00PM