Avalanche Forecast

Issued: Feb 12th, 2019 4:20PM

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

mbender, Avalanche Canada

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.

Summary

Confidence

High -

Weather Forecast

TUESDAY Night: Mainly cloudy with flurries, light southwest wind, alpine temperature -14 CWEDNESDAY: Cloudy with sunny breaks, light southwest wind, alpine temperature -13 C.THURSDAY: Mix of sun and cloud, light southeast wind, alpine temperature -10 C.FRIDAY: Flurries, accumulation 5-10 cm , light southwest wind, alpine temperature -7 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

New wind slabs have likely formed with recent southerly winds. Wind slabs from the weekend developed with northerly winds. Wind slabs may therefore be touchy on all aspects and at all elevation bands.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

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. Skiers have recently triggered large avalanches on these layers.

Be aware of the potential for wide propagation.Avoid steep, open and/or sparsely treed slopes at and below treeline.Any steep opening in the trees should be treated as suspect right now.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

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.

Avoid making assumptions about this layer based on aggressive tracks on adjacent slopes.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 13th, 2019 2:00PM