Archived

Avalanche Forecast

Mar 8th, 2017–Mar 9th, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Purcells.

Storm slabs are primed for people triggering large avalanches, and have the potential to step down to deeper persistent weaknesses resulting in very large and dangerous avalanches.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

THURSDAY: A mix of sun and cloud with increasing cloud and wind late in the day as the next system moves into the region.FRIDAY: Cloudy with 10-20cm of fresh snow accompanied by light to moderate SW winds. Alpine temperatures reaching -5 C.SATURDAY: A mix of sun and cloud with flurries bringing another 2-5 cm. Light to moderate SW winds and alpine temperatures around -5 C.

Avalanche Summary

Reports from Tuesday include one natural Size 2.5 on a southeast facing alpine slope in response to intense cross-loading as well as numerous other natural dry loose and soft slab avalanches up to Size 1 on lee aspects. Explosives control produced wind slab and persistent slab avalanches up to Size 3. One of which was 100-300cm deep, failing on the deep persistent facet/crust weakness buried in November.

Snowpack Summary

A wide ranging 50-100 cm of fresh snow has fallen in the past week, which is bonding poorly to weak faceted snow and small surface hoar. Southerly winds have formed touchy slabs at all elevations with multiple weaknesses within and under this recent storm snow. The persistent weakness buried mid-February is now down 60-120 cm and composed of a thick rain crust as high as about 2000 m, sun crusts on steep southerly aspects, and spotty surface hoar on shaded aspects. This layer has produced easy results in recent snowpack tests and has proven especially reactive on steep southerly aspects. Several deeper persistent weaknesses also remain a concern, including surface hoar buried early-February (80-140 cm deep), and mid-January (over a metre deep primarily in the northern Purcells ). Basal facets may still be reactive in shallow, rocky start zones.

Avalanche Problems

Storm Slabs

Weaknesses within and under the 40-100 cm of recent storm snow are susceptible to human triggering. These storm slabs are particularly deep and touchy on slopes loaded by southerly winds.

Be increasingly cautious as you transition into wind affected terrain.Be alert to conditions that change with elevation.If triggered, storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 2 - 3

Persistent Slabs

Several persistent weak layers buried 75-140 cm deep remain a concern, especially while touchier storm slabs carry the risk of 'stepping down' to one of these deeper weak layers. The greatest risk exists in shallow snowpack areas.

Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Avoid steep convexities or areas with a thin or variable snowpack.Be aware of overhead hazards and avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 4