Avalanche Forecast

Issued: Feb 15th, 2019 5:09PM

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

jfloyer, Avalanche Canada

Purcells.

It is possible the south of the region could see more snow than forecast. If amounts exceed 15 cm, consider this region considerable.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

FRIDAY NIGHT: 5-10 cm of low density snow expected, with more likely in southern areas. Mostly light winds.SATURDAY: Around 5 cm new snow. Treeline temperatures around -8C. Light northeasterly winds.SUNDAY: Dry and cloudy. Treeline temperatures around -11C. Light northeasterly winds.MONDAY: Dry, with some clear spells. Treeline temperatures around -12C. Moderate northwesterly winds.

Avalanche Summary

Reports on Tuesday, Wednesday and Thursday 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

10-20 cm recent low density snow has been blown around by strong northeasterly winds, creating touchy wind slabs in exposed areas. This new snow sits above wind-affected snow and/or sugary facets. In the far south of the region (south of Cranbrook) recent storm amounts are more like 30-40 cm of new snow. 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 deeper (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

Recent strong winds from the northeast have set up wind slabs on unusual southerly and westerly aspects. Previous old wind slabs on other aspects are likely reactive too.

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: Alpine, Treeline.

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

Valid until: Feb 16th, 2019 2:00PM