Avalanche Forecast

Issued: Apr 24th, 2017 4:00PM

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

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Mainly cloudy skies should keep heating to a minimum at upper elevations but watch for daily heating to break down crusts below treeline where recent heating has weakened the snowpack.

Summary

Weather Forecast

Strong solar heating on Sunday added heat to the snowpack. A decent refreeze was found Monday morning and while heating was progressing rapidly at first, snow squalls moving though some areas turned this around. Expect another 5 to 10 cm by the end of Tuesday and mainly cloudy skies through Thursday which will hopefully keep heating in check

Snowpack Summary

Up to 10 cm overnight and today brought by local squalls. At treeline and above, melt freeze crusts exist to ridge top on solar aspects, while on north aspects, dry surface snow still exists above ~2300m. Below 2000m the snowpack becomes wet during the day and is becoming isothermal. The weak basal facets remain a concern mainly in alpine areas.

Avalanche Summary

Sunday, Forecasters received a report of a party of 2 being involved with a size 2 avalanche that was cornice triggered in a N facing couloir by Boom Lake. Both party members were caught by snow that the cornice entrained, and partially buried. One skier was carried further than the other and sustained minor injuries and a lost ski pole.

Confidence

Problems

Loose Wet

Heating Sunday created moist snow below 2000m and isothermal snow on solar aspects BTL with crusts forming overnight. Although forecasts are calling for cloud, expect even brief solar inputs or rain to start breaking these crusts down.

Pay attention to sluffing off cliffs and steep solar terrain, signs of a warming snowpack.If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Cornices

Cornices continue to fail. Minimize your time underneath these and remember that a cornice failure could also trigger the deep persistent slab on the basal facets.

Give cornices a wide berth when travelling on or below ridges.Cornices become weak with daytime heating, so travel early on exposed slopes.

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

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Deep Persistent Slabs

The snowpack is gaining strength, but the weak basal facets continue to produce sudden collapse results and can produce large avalanches with large triggers or heat. Stick to planar, supported slopes with a deeper snowpack when entering steep terrain

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Valid until: Apr 25th, 2017 4:00PM