Archived

Avalanche Forecast

Dec 25th, 2018–Dec 26th, 2018

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

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

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

Regions: South Rockies.

Persistent slabs are tricky to manage and generally require patience and conservative terrain choices. Check out the new Forecaster Blog for a great explanation on how to best manage a persistent slab problem. Click here to read the blog.

Confidence

Moderate -

Weather Forecast

TUESDAY NIGHT: Clear. Light west-southwest wind. Alpine low of -12C.WEDNESDAY: Cloudy with isolated flurries, trace accumulation. Light southwest wind. Alpine high of -9C.THURSDAY: Mix of sun and cloud, isolated flurries, trace accumulation. Light northwest wind. Alpine high of -11C.FRIDAY: Mix of sun and cloud. Light increasing to moderate west wind. Alpine high of -10C.

Avalanche Summary

On Sunday, explosives and skier traffic triggered wind slab avalanches to size 2. On Saturday, explosives triggered avalanches on the persistent weak layer to size 2.5. One natural size 2 avalanche that was triggered by a cornice was reported in the region on Friday.

Snowpack Summary

Strong to extreme winds have redistributed new snow in the alpine and treeline, stripping areas exposed to the wind and creating hard wind slabs in wind-loaded terrain. In total, 60-90 cm of recent snow has formed a slab that sits on a persistent weak layer of facets (sugary snow) that formed during the dry weather in early December. Though avalanche activity on this layer has slowed down in recent days, it may still be easy for humans to trigger avalanches on this layer in certain terrain features. Steep features where the underlying ground cover is smooth, places where the snowpack depths are variable, and large convex features are some of the more likely places to trigger this layer.The lower snowpack has a weak structure composed primarily of facets. It is likely that an avalanche triggered on the persistent slab would step down to the lower facets, resulting in a full depth avalanche.

Avalanche Problems

Persistent Slabs

60-90 cm of snow sits on a weak layer of facets (sugary snow). The snow below this layer consists primarily of facets all the way to the ground. Avalanches triggered on this layer will likely step down to the ground, resulting in large avalanches.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 2 - 3

Wind Slabs

Watch for wind slabs in lee and open terrain. Strong to extreme winds have redistributed snow.

Pay attention to overhead hazards like cornices which could trigger persistent slabs.Travel on ridgetops to avoid wind slabs on slopes below.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1.5