Archived

Avalanche Forecast

Mar 11th, 2017–Mar 12th, 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

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

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: Lizard-Flathead.

Conditions are tricky with a complex mix of avalanche problems and weather factors. Err on the side of caution when dealing with such uncertainty.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

SATURDAY NIGHT: Passing frontal system brings 10-20 cm of new snow overnight with strong southwest winds.SUNDAY: Light flurries easing off throughout the day, moderate southwest winds, alpine temperatures around -4 C.MONDAY: Cloudy with isolated flurries, moderate to strong southwest winds, freezing level rising to around 1700 m.TUESDAY: Cloudy, moderate southwest winds, freezing level around 1900 m.

Avalanche Summary

A storm cycle occurred on Friday, producing numerous natural size 2-3 avalanches (including some triggered by cornice falls) and several size 1-2 skier-triggered avalanches. Activity tapered off on Saturday, but explosive control produced numerous size 2-2.5 avalanches. Earlier in the week, a size 3.5 avalanche on Mt. Hosmer was a sign the deep persistent slab problem may persist.New snow will form fresh storm slabs on Sunday, while warming and loading may stress cornices and deeper weaknesses.

Snowpack Summary

Warm temperatures from an alpine inversion have rapidly settled the most recent 40 cm of storm snow. Southwest winds over the past few weeks formed large cornices on alpine ridges. March has delivered regular storms with roughly 80-120 cm of snow sitting above crust and facet interfaces from February. Little is known about the reactivity of these interfaces, although no recent avalanches have been reported on these layers. Isolated basal facets still exist in shallow snowpack areas and can produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls, rapid warming, or strong solar radiation.

Avalanche Problems

Storm Slabs

Another round of snow on Saturday night will form fresh storm slabs that will be thickest and most reactive in wind-exposed terrain.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be cautious as you transition into wind affected terrain.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Cornices

Cornices are huge and are ripe for triggering. To avoid a nasty ride, give these monsters a wide berth when traveling along ridge crests.

Even small cornice falls may trigger larger avalanches.Minimize exposure to overhead hazard from cornices.Extra caution needed around cornices with current conditions.

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

Elevations: Alpine.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Deep Persistent Slabs

Storm loading and warming may increase the likelihood of triggering large deep persistent slab avalanches.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for large, deep avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 4