Avalanche Forecast Purcells

Sunday 10th February 2019

Avalanche Danger Ratings Sun 10th Feb 4:44PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Moderate Danger Ratings Below Treeline: Moderate Wind Slabs Wind Slabs Persistent Slabs Persistent Slabs Deep Persistent Slabs Deep Persistent Slabs

Avalanche Canada Forecaster: dsaly

Date Issued:

Valid Until:

Watch for wind slabs in unusual locations. Large avalanches may remain sensitive to human triggering due to the presence of buried surface hoar. See our Forecasters' Blog for a more detailed description of current conditions here.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

SUNDAY NIGHT: Cloudy with clear periods. Alpine temperatures near -18C. Ridgetop winds light from the south.MONDAY: Mix of sun and cloud with isolated flurries, trace accumulation. Alpine temperatures near -14C. Ridgetop winds light from the south.TUESDAY: Cloudy with scattered flurries, 5-15 cm accumulation. Alpine temperatures near -10C. Ridgetop winds moderate from the south.WEDNESDAY: Cloudy with scattered flurries, 5-10 cm accumulation. Alpine temperatures near -8C. Ridgetop winds light to moderate from the southeast.

Avalanche Summary

On Saturday a skier remote triggered a size 1 wind slab on a south/southeast facing slope at 2500 m.On Friday a skier in the "Molars South" zone near Golden accidentally triggered a size 2 avalanche on a southeast facing slope at 2300 m with a crown 40 to 50 cm in depth, the mid January persistent weak layer was likely in play. Also on Friday, a natural size 1 persistent slab avalanche was reported from an east facing slope at 1900 m. Finally, a natural size 1 wind slab avalanche was reported from an east facing slope at 2300 m on Friday. The mid-January persistent weak layer continues to be sensitive to human triggering and is sensitive enough to trigger remotely (from a distance). Human triggered avalanches size 1.5 to 2 were reported almost everyday last week. This MIN report from February 3rd illustrates the potential for humans to remotely trigger the mid January layer.

Snowpack Summary

Approximately 30-60 cm of old storm snow sits on, surface hoar (feathery crystals), facets (sugary snow) and a crust on sun-exposed slopes. A very notable feature in the snowpack is a persistent weak layer that was buried in mid January, which is now 50-90 cm below the surface. This layer consists primarily of surface hoar, however there is also a crust associated with it on sun-exposed slopes. This layer has been most reactive at treeline and below.The base of the snowpack has a deep persistent weak layer near the ground. This layer consists of facets over a crust. This weak interface continues to produce large and destructive avalanches that are sporadic in nature, and very difficult to predict. This layer 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 the kind of terrain to be wary of.

Wind Slabs Wind Slabs

Likelihood

Possible - Unlikely

Expected Size

1 - 2

30-60 cm of old storm snow has been redistributed by recent north and east winds, wind slabs may be found in unusual locations.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered, wind slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine.

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Persistent Slabs Persistent Slabs

Likelihood

Possible

Expected Size

1 - 2.5

50-90 cm of snow now sits on a weak layer of surface hoar and crust that was buried in mid January. This layer has been most reactive at lower elevations.

Choose low angled terrain.Any steep opening in the trees should be treated as suspect right now.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

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Deep Persistent Slabs Deep Persistent Slabs

Likelihood

Possible - Unlikely

Expected Size

3 - 4

The base of the snowpack has a very weak layer that continues to produce very large avalanches from time to time. The probability of triggering this layer is somewhat low, but the consequences are 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.

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