Avalanche Forecast

Issued: Mar 18th, 2017 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Avoid exposure to avalanche terrain: the new storm has resulted in another avalanche cycle today. Explosive Avalanche Control is planned for Mt Bourgeau, Mt Stephen and Mt Dennis. Please no climbing or skiing in these areas Sunday.

Summary

Weather Forecast

A significant storm is underway Saturday with moderate to strong SW winds, moderate precip and freezing levels in excess of 2200m. The storm will taper off Sunday morning and freezing levels are expected to drop back to valley bottom as winds shift back to westerly. A cooling trend will continue with light precip until skies start to clear Monday.

Snowpack Summary

10 to 20cm of new snow, combined with 40 to 80cm from the last 14 days has created a significant load over a fundamentally weak snowpack. Rain to 2200m, warmer overall temperatures, and snow in the alpine combined with strong SW winds are building superficial wind and storm slabs and overloading the deep basal facet layers. Poor travel below 2000m.

Avalanche Summary

Control work yesterday on the 93 S produced surprisingly large results reaching historical runnouts to sz 3.5. Extensive Natural activity has been seen on flights throughout the forecasting region to size 4 with fracture lines longer than 1km in many locations. Reports today indicate new activity to the same scale as the latest storm hits.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

Problems

Deep Persistent Slabs

The entire snowpack is built upon a structurally weak base, which has been overloaded by new snow and previous rain. Large avalanches are reaching historical run outs and crossing cross country ski trails.

Be aware of thin areas that may propogate to deeper instabilites.Be wary of slopes that did not previously avalanche.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

3 - 4

Wind Slabs

Wind slabs over 1m deep exist at higher elevations, and in wind effected areas near treeline. This slab reacts easily to tests and continues to produce avalanches. Correspondingly cornices have grown significantly and are fragile.

Be aware of the potential for wide propagations.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

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

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

2 - 3

Loose Wet

With freezing levels in excess of 2200m Saturday, the surface snow at lower elevations has been failing naturally. Deeper avalanches could be triggered by these events as the entire snowpack has lost strength and will take some time to refreeze.

Use extra caution on slopes if the snow is moist or wet.If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Mar 19th, 2017 4:00PM