Avalanche Forecast

Issued: Apr 21st, 2017 8:00AM

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

danyelle magnan, Parks Canada

Glacier.

It's been days since we've had an overnight crust recovery. If the sun comes out full force today as forecast, it will rapidly destabilize the snowpack and will increase the likelihood of cornice failures.

Summary

Weather Forecast

Today we will get increasing sun and freezing levels to 2100m. Winds will be light and won't help to cool temps. Freezing levels should drop overnight providing an overnight recovery. Sat we will see increasing cloud with light precip, and freezing levels to 2200m. Sun will be a cloudy with sunny breaks, some flurries, and freezing levels at 1900

Snowpack Summary

Below treeline there hasn't been an overnight recovery several days, with wet snow overlying and bonding poorly to a crust. Yesterday moist, mashed-potato like snow was reported to 2400m on even N aspects. It rained to at least 1900m, with ~4mm of rain changing to snow overnight. At ridgetop moderate S'ly winds will have loaded lee slopes.

Avalanche Summary

Several naturally triggered avalanches to size 2.5 were observed along the highway corridor. They were all loose, wet avalanches. A few avalanches gouged to ground once they reached the weak, isothermal snow at low elevations. Skiers have reported the top 20cm is easily triggered below treeline, with wet snow running on the crust below.

Confidence

Timing or intensity of solar radiation is uncertain

Problems

Wind Slabs

At high elevations, moderate S-SW winds will have formed windslabs in the immediate lee of ridges and cross-loaded features. In many areas, these windslabs overlie crusts and may be easily triggered.

Use caution in lee areas. Recent wind loading have created wind slabs.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Loose Wet

At treeline and below temps have been remaining warm, preventing crust formation overnight. The result is very weak and wet surface snow, which sits and slides easily on the crusts below. Sunshine today will weaken the snowpack further.

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

Possible - Likely

Expected Size

1 - 3

Cornices

Huge cornices loom over many slopes. Strong solar today is expected to weaken these monsters and may cause them to fail. Cornices are the most likely trigger for deep persistent slabs, resulting in very large avalanches.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Apr 22nd, 2017 8:00AM