Avalanche Forecast

Issued: May 6th, 2017 5:31PM

The alpine rating is below threshold, the treeline rating is below threshold, and the below treeline rating is below threshold. Known problems include Wet Slabs, Deep Persistent Slabs and Cornices.

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Widespread Natural Avalanches continued through Saturday. Cooling Sunday should slow this activity but the snowpack will not completely recover by the time the sun returns on Monday. AVOID ALL AVALANCHE TERRAIN even if you are just hiking down low.

Summary

Weather Forecast

Rain and with high freezing levels continued to add heat to the snowpack Saturday. Cooler temps Sunday morning should lead a light freeze TL and above with 5 to 10 cm accumulating. Rain will likely keep travel poor BTL. The first freeze to valley bottom in quite a while is forecast for Monday however solar inputs may quickly weaken new crusts.

Snowpack Summary

Moist surface snow to mountain top for all but the highest peaks. Un-supportive, isothermal conditions exist to around 2500m. The basal weakness persists in the alpine and at treeline and is reactive to large triggers and has been failing with the warm temperatures, solar inputs and rain over the last 4 days. Travel is poor.

Avalanche Summary

Avalanches are running far initiating as wet slabs at TL or the alpine as wet slabs and running well below treeline into hiking terrain. Thursday explosive brought down size 3-4 wet slab avalanches from the alpine over bare ground BTL. It's a good time to AVOID AVALANCHE TERRAIN completely.

Confidence

Problems

Wet Slabs

Both loose wet and wet slab avalanches are occurring on all aspects and elevations and many have run over bare ground BTL. These will likely continue with rain BTL Sunday but will become more widespread again when the sun returns Monday.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

We expect natural activity to taper off with cooling however the deep facets will remain sensitive to human triggering until the snowpack can fully refreeze.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 4

Cornices

Cornices have taken quite a hit with the recent heat, many are cracked and peeling off of ridges. These should all be considered as suspect as they WILL fall of in the coming weeks.

Cornices become weak with daytime heating, so travel early on exposed slopes.Pay attention to overhead hazards like cornices which could trigger the deep persistent slab.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Likely

Expected Size

2 - 3

Valid until: May 7th, 2017 4:00PM