Avalanche Forecast

Issued: Mar 23rd, 2016 8:26AM

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

Alberta Parks matt.mueller, Alberta Parks

Terrain selection and route finding is key out there. Good situational awareness and discipline are crucial for this week or until the snowpack gets into spring mode. The snowpack is highly complex so do not fool yourself into believing otherwise.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

The Jet stream is to the north of the Rockies at moment.  Tonight the winds are forecast to be strong out of the west through the evening.  Winds will taper in the am and the freezing levels are set for 1600 meters with trace precipitation in the next 24 hrs.

Avalanche Summary

Yesterday Banff Visitor Safety Forecasting team did avalanche control on the Bourgeau 4 path and got a size 2.5 slab avalanche result.  Temperatures were cool this morning but freeze levels have been in the 1800-2000 meter range so activity coincides with the sun and warming air in the afternoon.  Pay attention to the daytime heating and any new storm loads over the next while.

Snowpack Summary

We continue to see evidence that our snowpack is not yet a spring snowpack and still very much a winter snowpack.  The upper snowpack is complex with 4-5 melt form crusts that vary in depth from just below the surface and up to 80cm deep.  These melt form crusts, particularly the Feb11th crust are highly suspicious as we saw many large size 2.5-3.0 avalanches out of steep hanging alpine walls. some initiated by cornice failures and others failing with heat (solar or ambient air temperatures approaching zero degrees).  The second and biggest concern for us at the moment is the Jan 6th interface (facets) buried anywhere from 60-110cm in the snowpack - a legitimate deep Persistent Weak Layer.  This is the layer that is associated with the very long drought we had that started shortly after Dec 20th and extended into the 2nd week of January before another storm buried these facets.  This layer is showing highly variable results in snowpack tests and high degree of variability in its distribution.  Essentially we have a very low degree of confidence as forecasters in the snowpack.

Problems

Persistent Slabs

An icon showing Persistent Slabs
There are multiple melt form crusts in the upper to midpack and are producing variable results in snowpack tests. In spite of bonding interfaces, watch the warming inputs such as solar and increasing freezing levels on wind slabs over these crusts
Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Shallow snowpack areas need to be monitored  and avoided as you travel through treeline and alpine terrain.  Really good idea to stay well away from large scale alpine features, especially in the presence of  looming cornices
Be aware of the potential for wide propagations due to the presence of hard windslabs.>Be wary of slopes that did not previously avalanche - even on low angle terrain.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 6

Cornices

An icon showing Cornices
They are much bigger than you, they will trigger monster avalanches based on what we have seen this past 2 weeks - give them LOTS of space and as little of your exposure time as is possible.
Stay well back from cornices.>Avoid steep slopes below cornices.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

3 - 6

Valid until: Mar 24th, 2016 2:00PM

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