Avalanche Forecast

Issued: Apr 13th, 2017 3:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Storm Slabs, Cornices and Persistent Slabs.

triley, Avalanche Canada

South Columbia.

New storm slabs have developed at higher elevations. Forecast changing wind directions may result in reverse loading.

Summary

Confidence

Moderate - Wind speed and direction is uncertain on Friday

Weather Forecast

Overnight: 5-15 cm of new snow with moderate southwest winds and freezing down to 800 metres. Friday: Overcast with another 5-8 cm of snow combined with moderate west winds and daytime freezing up to 1600 metres. Saturday: Overcast with flurries and moderate west winds and daytime freezing up to 1500 metres. Sunday: Mostly sunny with light winds and daytime freezing up to 1900 metres.

Avalanche Summary

Thin storm and wind slab avalanches were reported up to size 1.5 early in the storm on Wednesday. One deep persistent slab avalanche size 3.0 was reported on Tuesday from the Selkirks, there was no information regarding aspect or elevation. Natural cornice falls were reported up to size 3.0 on Monday.

Snowpack Summary

The new storm slab is now 20-30 cm deep, and the snow arrived with east or southeast winds. The wind is forecast to change to the west, and this may result in reverse loading. This new now is sitting on the 30-50 cm of recent snow from the past week. The new and recent snow are covering a mix of old surfaces, including several crusts on all aspects at treeline and below, and on solar aspects in the alpine. Cornices continue to be reported to be large and fragile, and the have released naturally on a regular basis. The February weak layers are now down about 170-220 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers produced large avalanches with cornice falls and other heavy triggers in late March and early April. Yet another deep release was reported in the region on Saturday. This activity, although growing more sporadic, is keeping these layers an ongoing concern. They may be more likely to fail on southerly aspects during periods of strong solar radiation.

Problems

Storm Slabs

Changing wind directions may result in pockets of wind transported snow on several aspects in the alpine and at treeline. Continued rain at lower elevations may result in loose wet avalanches in steep terrain.

Use ridges or ribs to avoid pockets of wind loaded snow.Keep an eye out for reverse loading created by shifting winds.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Cornices

Cornices have grown large and may fall off naturally with solar effect or daytime warming. Cornice falls were responsible for triggering a number of large persistent slab avalanches last week and as recently as Saturday.

Avoid travel on slopes that are exposed to cornices overhead.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Persistent Slabs

A cornice fall or smaller slab avalanche has the potential to trigger large, destructive avalanches on deeply buried weak layers. This is more likely to occur in thin or variable snowpack areas when the sun is out and solar radiation is strong.

Recognize and avoid avalanche runout zones.Cornices or smaller slab avalanches could step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 4

Valid until: Apr 14th, 2017 2:00PM