Avalanche Forecast

Issued: Dec 19th, 2018 4:00PM

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

grant statham, Parks Canada

Banff Yoho Kootenay.

The second avalanche cycle within one week starts on Thursday with large amounts of new snow overlying significant weak layers. Avoid avalanche terrain until the weekend at least and expect road closures - highway avalanche control will be ongoing.

Summary

Weather Forecast

The last in a series of westerly storms will cross the region starting overnight on Wednesday and picking up steam through the day on Thursday. Expect 10-15 cm by the end of the day Thursday (25 on the Wapta), and 20-30 cm by Friday morning (up to 50 on the Wapta). Clearing on Friday evening and temperatures dropping to -18 by Saturday.

Snowpack Summary

10-15cm of low density storm snow has fallen in the last 48-hours with the 8-day total reaching 60-80 cm. Add another 20-40 cm by Thursday and we have a significant storm slab development - the snowpack has almost doubled in the last week. The Dec 10 persistent weak layer was found in Crowfoot Glades down 80 cm giving sudden planar test results.

Avalanche Summary

Numerous natural avalanches observed today in the Bow Summit area: size 2.5 natural cornice on Bow Peak; size 2.5 deep slab under the Crowfoot Glacier; size 2.5 natural off Jimmy Junior; size 1.5 skier remote in the Observation Peak trees. This pattern can be expected everywhere in the park right now. Lots of avalanches happening.

Confidence

Due to the number and quality of field observations

Problems

Storm Slabs

Another 30-50 cm of snow is forecast by Fri morning adding to the storm slab. Avoid avalanche terrain. Expect natural avalanches to run down into the treeline. Safe terrain can be found in low angled forest with no exposure to avalanches from above.

Avoid all avalanche terrain.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

The mid and lower portions of the snowpack are weak and are now overloaded with critical levels of snow. We expect avalanches to step down to these deeper layers of facets and depth hoar. Avoid avalanche terrain.

Good day to make conservative terrain choices.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1.5 - 3

Valid until: Dec 20th, 2018 4:00PM