Avalanche Forecast

Issued: Mar 25th, 2017 4:00PM

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

william lawson, Parks Canada

Banff Yoho Kootenay.

The sun will pack a punch at all elevations, be weary that solar inputs can affect deep instabilities at higher elevations and deteriorate the snowpack structure below treeline.

Summary

Weather Forecast

A diurnal weather pattern is forecasted for Sunday, Monday with daytime highs at valley bottom approaching 10 degrees and lows below freezing. Expect short convective pulses bringing in snow and rain, with mostly clear skies Sunday.

Snowpack Summary

Dense, rounded snow comprises the upper half of the snowpack and sits on a very weak base of depth hoar. This unstable structure produces consistent, sudden collapse test results in the lower snowpack. Wind slab continues to developer at tree line and above. Below treeline a melt freeze cycle is developing, with the snowpack weakening in PM.

Avalanche Summary

The natural activity has decreased over the last few days however daily reports of activity continue to come in, Na size 3 observed on 93S in the Numa falls area suspect cornice trigger today. It appears to take only very small inputs of sun, wind or precip to trigger natural events and artificial / human triggering should be considered likely.

Confidence

Problems

Deep Persistent Slabs

Natural activity has decreased, but the snowpack is considered very suspect right now. Large avalanches initiating TL and above have recently run to valley bottom with crowns up to 2m + deep. Suspect increase reactive with solar inputs.

Be wary of slopes that did not previously avalanche.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Wind Slabs

Wind transport continues to load lees features. Expect the fresh slabs that have formed at higher elevations to be easy to trigger. Expect the new growth on cornices to be fragile.

If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Loose Wet

Strong solar inputs and increased daytime highs will deteriorate the snowpack structures below tree line. Take note of overnight refreezes, and strength of the sun effect on steep solar aspects.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 26th, 2017 4:00PM