Avalanche Forecast

Issued: Feb 14th, 2019 5:08PM

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.

There is uncertainty for snowfall amounts in the far south of the region (Cranbrook and south) Thursday night into Friday. If local amounts are 30 cm or more avalanche danger will be HIGH.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

THURSDAY Night: Cranbrook and south - Snow, accumulation 15-30 cm possible, light to moderate southeast wind, alpine temperature -9 C.Further north - Mainly cloudy with isolated flurries, light to moderate southeast wind, alpine temperature -9 C.FRIDAY: Flurries, accumulation 5-10 cm , light to moderate southwest wind, alpine temperature -8 CSATURDAY: Flurries, accumulation 5-10 cm, light west wind, alpine temperature -9 CSUNDAY: Mix of sun and cloud, light northeast wind, alpine temperature -13 C

Avalanche Summary

Reports on Tuesday and Wednesday include a few wind slab avalanches size 1-2 on north, south and east aspects in the alpine. There were also a few storm slab avalanches reported to size 1 at treeline. Additionally on Wednesday there was a cornice triggered size 3 deep persistent slab reported on a northeast aspect at 2800m.

Snowpack Summary

In much of the region 5-15 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 45 cm+ of new snow has accumulated in the past 3 days. Lingering windslabs at tree line and in the alpine may still be reactive in areas further north.

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

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.

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

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Deep Persistent Slabs

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

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 3.5

Valid until: Feb 15th, 2019 2:00PM