Avalanche Forecast

Issued: Dec 9th, 2017 3:39PM

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

jlammers, Avalanche Canada

Northwest Coastal.

Forecast freezing levels and precipitation amounts are highly uncertain for Sunday. Pay close attention to how much rain or snow falls in your area and be prepared to back off to simple terrain.

Summary

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

Saturday night: 5-20cm of new snow with rain at lower elevations / Strong to extreme southerly winds / Freezing level at 1800mSunday: 5-30mm of precipitation / Strong to extreme southerly winds / Freezing level at 2400mMonday: Clear skies / Strong to extreme southerly winds / Freezing level at 2400mTuesday: Trace amounts of new snow / Light variable winds / Freezing level at 1200m

Avalanche Summary

On Friday, warm temperatures and sunshine initiated numerous loose wet avalanches to Size 1.5 on steep solar aspects in the alpine around the Terrace area. Warming also triggered a few deep persistent slabs to size 3 out of steep south facing alpine terrain. Basal facets were though to be the culprit in these events. Looking forward, forecast snow and wind will likely promoted a round of storm slab activity in higher elevation terrain. In areas where rain falls, loose wet avalanches may continue to run in steep terrain .Avalanche and snowpack data is extremely sparse at this time. Please submit your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Up to 5mm of rain fell in the Skeena corridor on Friday night. At higher elevations I suspect snow fell and was shifted by strong winds into wind slabs in lee terrain. In the Bear Pass area where temperatures were cooler, around 15cm of new snow fell down to near valley bottom. These accumulations overlie melt freeze crusts and possibly surface hoar.Another layer of large surface hoar that was recently observed in the Shames area is now buried about 15 cm below the surface. Information on the distribution and reactivity of this layer is limited. Below it, storm snow received last week is gradually settling above a 5-10 cm thick crust (November 23) down roughly 70-100cm. 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. The base of the snowpack is reported to be a mix of facets and melt-freeze crusts..

Problems

Storm Slabs

Fresh storm slabs will begin to build as a storm pulse brings snowfall with strong winds. Poor bonding may occur at the surface, so slabs may be touchy. Expect thicker, more dangerous slabs in coastal areas and on lee aspects.

Use extra caution in lee areas in the alpine and treeline. Storm snow will form touchy slabs.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Loose Wet

Rain on Sunday may cause small loose wet avalanches to occur, mainly in steep terrain and where rain or moist new snow accumulates.

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: Alpine, Treeline.

Likelihood

Possible - Likely

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. Releasing a thick storm slab or wind slab in the right location may provide enough of a trigger to step down a deep early season weakness.

Take extra caution around areas with a thin or variable snowpack.If triggered, storm slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 10th, 2017 2:00PM