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Avalanche Forecast

Dec 21st, 2018–Dec 22nd, 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 Columbia.

Avalanches are most likely on steep and convex terrain features, especially those that have been loaded by the wind.

Confidence

High.

Weather Forecast

FRIDAY NIGHT: Mostly clear skies, moderate wind from the northwest, alpine temperatures drop to -14°c. SATURDAY: Clear in the morning then increasing cloud throughout the day, light wind from the south, alpine high temperatures around -6°c. SUNDAY: Scattered flurries with 5-10 cm of snow, moderate wind from the southwest, alpine high temperatures around -6°c. MONDAY: Mostly cloudy with isolated flurries, light wind from the southwest, alpine high temperatures around -6°c.

Avalanche Summary

Isolated natural avalanche activity was reported on north aspect in the alpine during the windy storm on Thursday. Skiers were able to trigger small slabs on all aspects in the 10-30 cm of most recent snow. None of the avalanches reported on Thursday or Friday involved persistent slab problems, but earlier in the week there were a few large persistent slab avalanches (size 2-2.5) that were triggered remotely from adjacent slopes (most recently on Wednesday in the Valhallas). We can't rule out the possibility of deeper layers still being reactive to human triggers, as these layers are still adjusting to the weight of the new snow.

Snowpack Summary

Strong wind from the southwest has formed fresh wind slabs in the alpine and around treeline. A week of stormy weather has deposited 70-100 cm of snow above a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects) that formed during the dry spell in early December. This layer has been responsible for large persistent slab avalanches over the past week, particularly on north and east facing slopes above 1900 m. The potential exists for smaller avalanches to step down and trigger this deeper layer, resulting in very large avalanches. Another weak layer from mid-November is now buried up to 120 cm, but has been less active recently. It could potentially remain a concern on steep south-facing slopes where the surface hoar sits on a sun crust. At the base of the snowpack is a crust that formed in late October. The probability of triggering this layer is low, but the most suspect areas would be steep rocky alpine features with a shallow snowpack.

Avalanche Problems

Wind Slabs

Recent snowfall accompanied with strong wind from the southwest has left open and lee terrain covered with touchy wind slabs.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.The new snow will require several days to settle and stabilize.Use ridges or ribs to avoid pockets of wind loaded snow.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Persistent Slabs

A widespread weak layer buried 50-100 cm deep has the potential to produced large avalanches, especially on sheltered north and east facing slopes.
Remote triggering is a concern, watch out for adjacent slopes.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Use caution on open slopes and convex rolls

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3