Avalanche Forecast

Issued: Dec 13th, 2017 3:44PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Loose Wet, Storm Slabs and Deep Persistent Slabs.

swerner, Avalanche Canada

Northwest Coastal.

Upgrade the danger rating to CONSIDERABLE if you receive more than 20 mm of precipitation in your local riding area Thursday morning.

Summary

Confidence

Moderate - Track of incoming weather systems is uncertain on Thursday

Weather Forecast

Thursday: Cloudy with light precipitation starting late in the am. Alpine temperatures high plus 4 degrees and freezing levels 1400 m. Ridgetop wind light gusting strong from the southwest.Friday: Mainly cloudy. Up to 5 cm of new snow. Alpine temperatures -2 and freeing levels 1000 m. Ridgetop wind moderate from the southwest.Saturday: Heavy snow, 20-40 cm. Alpine temperatures -2 and freezing levels 1000 m. Cloudy with sunny periods. Ridgetop wind mostly light, with strong gusts from the southwest.Check out the Mountain Weather Forecast for more detail.

Avalanche Summary

No new avalanche observations reported on Wednesday. Avalanche activity will likely increase through the forecast period with new rain, snow and wind.I'd also remain suspect of the deep persistent layers on your radar as the region receives this new load. 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 deep persistent slab is something to keep on your radar, especially with more weather in the forecast.

Snowpack Summary

Recently, the region has received up to 20 mm of rain and some new snow at high alpine elevations. The alpine and treeline has seen significant wind effect on all aspects including wind slab and wind pressed snow. Snow surfaces are highly variable and consist of rain crusts, moist snow and new dry storm snow at elevations above 1700 m. Below the surface sits a well-settled snowpack overlying several layers of interest. Down 70-100 cm you'll likely find a 5-10 cm thick crust which was buried on November 23 and in some areas, a feathery surface hoar layer down 50-60 cm producing moderate snowpack test results. The widespread crust/facet interface that was buried at the end of October can now be found 100-200 cm deep and exists region wide.

Problems

Loose Wet

With continued warming and light precipitation, loose wet avalanches are possible until the freezing level drops on Friday, especially on steep slopes and terrain features.

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

Possible

Expected Size

1 - 2

Storm Slabs

Storm slabs may exist where the precipitation falls 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

Valid until: Dec 14th, 2017 2:00PM