Archived

Avalanche Forecast

Mar 20th, 2017–Mar 21st, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Lizard-Flathead.

A capping crust may hold deep persistent slab problems at bay on Tuesday. Expect a different set of hazards at alpine elevations and be aware of the potential consequences of releasing a heavy trigger.

Confidence

Moderate -

Weather Forecast

Tuesday: Cloudy with scattered flurries bringing up to 5 cm of new snow, with light rain climbing to about 1600 metres. Light south winds. Freezing level rising to 2000 metres with alpine temperatures around 0. Wednesday: Cloudy with isolated flurries and a trace of new snow, light rain below about 1600 metres. Strong southwest winds. Freezing level to 2000 metres with alpine temperatures around 0. Thursday: A mix of sun and cloud. Moderate to strong southwest winds. Freezing level to 1700 metres with alpine temperatures around -2.

Avalanche Summary

No new avalanches were reported on Sunday. but reports from Saturday included observations of one naturally triggered Size 3 deep persistent slab as well as numerous natural storm slab releases occurring on northeast to northwest aspects just west of Fernie. Reports from Friday showed explosives triggered persistent slabs (and one storm slab) running from Size 2.5-3. Crown fractures generally ranged from 100-200 cm. On Thursday, storm slabs were observed releasing naturally to Size 2, with explosives control yielding deep persistent slabs to Size 3. Most crown fractures measured about one metre but one impressive storm slab featured a three metre fracture depth. North to northeast aspects were the main performers over both days.Looking forward, recently formed storm slabs at alpine elevations may remain reactive to natural and human triggering on Tuesday, especially as temperatures rise. While recent strong crust recovery has been tempering the likelihood of persistent slab activity, the rise in freezing levels and forecast rain may prompt renewed persistent slab activity.

Snowpack Summary

Stormy weather on Saturday formed fresh storm slabs at high alpine elevations while rain once again saturated the snowpack at lower alpine elevations and below. Lower temperatures have since formed a roughly 5-10 cm thick crust at the rain soaked surface, which tends to break down with daytime warming at lower elevations and on solar aspects. Isolated basal facets still exist in shallow snowpack areas and still carry the potential to produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls and storm slab avalanches, which may trigger naturally with daytime warming.

Avalanche Problems

Storm Slabs

Recent rain that soaked lower elevations fell as snow above about 2200 metres. Expect reactive storm slabs that thicken with elevation in the alpine and be aware that they are an overhead hazard to lower elevations, especially if they see rain.

Be alert to conditions that change with elevation.If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

Be careful not to overestimate the stabilizing effect of recent cool temperatures. Forecast warming will gradually increase potential for deep persistent slabs to release naturally or with a sufficient trigger on Tuesday

Recognize and avoid avalanche runout zones.Storm slabs or cornices may trigger deep layers and result in large avalanches.Avoid exposure to overhead hazards during periods of rain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 4

Cornices

Recent warm, stormy weather has seen cornices become huge and they are ripe for releasing as temperatures rise and if rain falls on Tuesday. Cornice falls are an excellent trigger for large persistent slab avalanches.

Avoid exposure to overhead hazard from cornices.Even small cornice falls may trigger larger avalanches.

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

Elevations: Alpine.

Likelihood: Likely

Expected Size: 1 - 3