Archived

Avalanche Forecast

Apr 18th, 2015–Apr 19th, 2015

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

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

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

Below Threshold

The avalanche danger rating in the alpine will be below threshold

Treeline

Below Threshold

The avalanche danger rating at treeline will be below threshold

Below Treeline

Below Threshold

The avalanche danger rating below treeline will be below threshold

Regions: South Coast.

Strong solar radiation, high freezing levels, and very warm temperatures may increase the avalanche danger rapidly. If there is no overnight re-freeze in your area, you should avoid avalanche terrain.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Mostly clear with light northwest winds overnight, and freezing levels dropping down to about 2000 metres. Sunny and warm on Sunday with a chance of some thin high cloud. Freezing level rising up to 2800 metres with temperatures around +10 expected in the alpine. Sunny and warm on Monday with freezing levels around 2800 metres. The ridge of high pressure is forecast to break down late Monday or early Tuesday allowing a weak westerly flow to move onshore bringing cloud and light precipitation.

Avalanche Summary

No new observations reported on Thursday or Friday. On Wednesday, natural cornice fall was reported, pulling thin slabs up to size 1 from the slopes below. Strong solar radiation and warming expected through the forecast period will likely initiate a natural avalanche cycle. Watch overhead hazards like cornice failures and solar induced loose wet, and slab avalanches.

Snowpack Summary

Anywhere from 20 to 40 cm of recent storm snow sits on a persistent weak layer comprising of crusts, surface hoar and facets which were buried April 10th. Moderate to strong south west winds are redistributing the storm snow into wind slabs on leeward slopes and terrain features. The mid-March persistent weak layer of facets on a crust is now approximately 50-100 cm down and continues to sit dormant. There is a low probability of triggering this layer, however; if it is triggered the consequence would be high. Large looming cornices may become weak with solar radiation and daytime warming. If a cornice fails it could trigger a large avalanche from the slope below.

Avalanche Problems

Persistent Slabs

Two persistent weak layers sit in the upper snowpack. One is down 20-50 cm and has been recently reactive naturally and to human triggers. The second one sits 50-150 cm down and may re-awaken with warming, cornice fall and step down avalanches.

Smaller surface avalanches and cornice fall could act as a trigger, initiating avalanches on the deeper buried weak layer.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 2 - 5

Cornices

Recent cornice growth has been observed and large cornices are expected to become weak with solar radiation and daytime warming. Cornices could trigger large slab avalanches.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood: Possible - Likely

Expected Size: 3 - 5

Loose Wet

Solar radiation and rising freezing levels will deteriorate the snowpack. Travel on sunny slopes early, and watch for obvious signs of instabilities like avalanches, moist surface snow and snowballing.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 3