Avalanche Forecast

Issued: Jan 26th, 2019 5:00PM

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

ghelgeson, Avalanche Canada

Purcells.

Avoid large terrain features such as alpine bowls and steep lines down from ridges where there is a chance of being caught in a very large avalanche. Updated Purcell Forecaster Blog here.

Summary

Confidence

Moderate -

Weather Forecast

Sunday marks the start of a pronounced ridge of high pressure that is expected to be with us through at least Tuesday. This period is marked by mostly clear skies, cooler temperatures and a lack of precipitation.SATURDAY NIGHT: Freezing level at valley bottom, light west/southwest wind at most elevations, extreme northwest wind at ridgetop, no precipitation expected.SUNDAY: A few clouds, freezing level beginning at valley bottom rising to around 1000 m during the day, moderate to strong northwest wind, no significant precipitation expected.MONDAY: Mostly clear skies, freezing level at valley bottom, light northwest wind, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light variable wind, no precipitation expected.

Avalanche Summary

On Friday wind slab avalanches up to size 2 were reported from east and northeast aspects between 2000 and 2400 m.One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here. Dealing with the deep persistent basal facet/crust problem requires avoiding terrain where this kind of avalanche is possible.

Snowpack Summary

Up to 20 cm of recent snow has buried large surface hoar crystals which, on southern aspects, may rest on a sun crust. In most places, there is still insufficient snow over this layer to create a widespread problem. However, locally, in deeper snowpack areas, or where the wind has blown snow above this layer, avalanches large enough to be of concern could be triggered. The snowpack also has a deeply buried weak layer near the ground composed of weak faceted grains and a crust that is present in most of the region. There have been sporadic reports of people triggering this layer in areas where the snowpack is shallow. The most likely trigger points include ridgelines, large open slopes and bowls in the alpine, particularly those that have rocky or variable (thin to thick) features. If you trigger a deep persistent slab it will go big and be a highly destructive avalanche.

Problems

Deep Persistent Slabs

Large destructive avalanches have consistently been triggered on deeply buried weak layers. This problem will exist for a while to come and is tricky to manage. Likely trigger points are shallow snowpack areas, such as near ridges and rocky terrain.

Choose supported, conservative terrain that is not connected to large overhead slopes.Avoid steep slopes and areas with a thin, variable snowpack.Watch for signs of instability such as whumpfing, cracking, or recent avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Wind slabs should be treated with caution in exposed areas, particularly as triggering something on the surface could step down to the deep persistent layer below.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be careful around freshly wind loaded features, especially near ridge crests and roll-overs.

Aspects: North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 27th, 2019 2:00PM