Archived

Avalanche Forecast

Dec 11th, 2017–Dec 12th, 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

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

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

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Northwest Coastal.

Continued warming and precipitation is adding stress to the snowpack and driving the danger rating.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Tuesday: Mainly cloudy with light snow in the alpine and rain showers below. Ridgetop winds moderate from the southwest. Alpine temperatures near 1 degree and freezing levels 1700 m.Wednesday: Mainly cloudy with isolated showers. Ridgetop winds light to moderate from the south. Alpine temperatures plus 5 degrees and freezing levels rising to 2200 m.Thursday: Snow amounts 10-20 cm in the alpine and rain below. Freezing levels near 1700 m. Ridgteop winds light with strong gusts from the south.

Avalanche Summary

On Sunday, rain and warmer temperatures initiated numerous natural loose wet and storm slab avalanches up to size 1 throughout the region. On December 7th and 8th a few deep persistent slabs to size 3 out of steep south facing alpine terrain in the Skeena corridor west of Terrace were reported. Basal facets were thought to be the culprit in these events. The Bear Pass area also saw a size 2.5 wet slab avalanche on Saturday. The deep persistent slab is something to keep on your radar, especially with more weather in the forecast.

Snowpack Summary

The past couple of days brought up to 15 mm total precipitation in the Skeena corridor. Given the mild temperatures, I suspect most of that precipitation fell as rain. At alpine elevations snow likely fell and moderate to strong winds are expected to have formed wind slabs in lee terrain. In the Bear Pass area where temperatures were cooler, around 30cm of new snow fell. These accumulations overlie melt freeze crusts and possibly surface hoar.About 70-100cm below the surface you'll likely find a 5-10 cm thick crust which was buried on November 23. Another layer of surface hoar (November 11) continues to be observed down approximately 140 cm in the Bear Pass area, showing some signs of improved bonding. The widespread crust/facet interface that was buried at the end of October can now be found 90-160 cm deep.

Avalanche Problems

Loose Wet

With continued warming and light precipitation, I would expect loose wet avalanches to occur, especially on steep slopes and terrain features well into the alpine.

Use extra caution on slopes if the snow is moist or wet.Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Storm Slabs

Storm slabs may exist where the recent precipitation fell as snow. Watch for triggering in higher elevation, wind-exposed terrain.

Be alert to conditions that change with elevation.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 2

Deep Persistent Slabs

Weak layers buried near the base of the snowpack can't be dismissed while new snow or rain load the surface. I'd limit my exposure to large overhead slopes, especially when the sun makes an appearance on Monday.

Avoid areas with overhead hazard.Take extra caution around areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3