Avalanche Forecast Purcells

Friday 8th February 2019

Avalanche Danger Ratings Fri 8th Feb 4:41PM Danger Ratings Alpine: Moderate Danger Ratings Treeline: Considerable Danger Ratings Below Treeline: Considerable Persistent Slabs Persistent Slabs Wind Slabs Wind Slabs Deep Persistent Slabs Deep Persistent Slabs

Avalanche Canada Forecaster: ghelgeson

Date Issued:

Valid Until:

Large avalanches continue to be sensitive to human triggering due to the presence of buried surface hoar. Click here to see our Forecasters' Blog for a more detailed description of current conditions.

Confidence

Moderate -

Weather Forecast

Cold, dry, arctic air continues to dominate the weather pattern for the foreseeable future.FRIDAY NIGHT: Freezing level at valley bottom, around -25 C in the alpine, potentially strong valley bottom wind event, light to moderate southeast wind in the alpine, trace of snow possible.SATURDAY: Scattered cloud cover at dawn with clouds steadily clearing through the day, freezing level at valley bottom, around -25 C in the alpine, light winds at most elevations, strong east wind at ridgetop, no significant snowfall expected.SUNDAY: Clear skies at dawn with cloud cover increasing throughout the day, freezing level at valley bottom, around -20 C in the alpine, potentially strong valley bottom wind event, light southwest wind in the alpine, no significant snowfall expectedMONDAY: Scattered cloud cover, freezing level at valley bottom, around -20 C in the alpine, light variable wind at all elevations, no significant snowfall expected.

Avalanche Summary

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.  This layer continues to be sensitive to human triggers. This layer is sensitive enough to trigger remotely (from a distance). Human triggered avalanches size 1.5 to 2 were also reported on Sunday, Monday and Thursday. This MIN report from Sunday illustrates the potential for humans to remotely trigger the mid January layer.

Snowpack Summary

Approximately 30-60 cm of recent new snow sits on wind slab, surface hoar (feathery crystals), facets (sugary snow) and a crust on sun-exposed slopes. A very notable feature in the snowpack at this time is a persistent weak layer that was buried in mid January, which is now buried 50-90 cm. 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.

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.

More
Wind Slabs Wind Slabs

Likelihood

Possible - Unlikely

Expected Size

1 - 2

30-60 cm of recent new snow has been redistributed by recent north and east winds.  Wind out of the east/southeast Friday night into Saturday may form wind slabs 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: North, South East, South, South West, West, North West.

Elevations: Alpine.

More
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.

More
Offline, Anywhere Members can email a forecast to themselves, meaning it's available offline Join