Avalanche Forecast

Issued: Dec 10th, 2017 3:56PM

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

jlammers, Avalanche Canada

Northwest Coastal.

Forecast freezing levels are highly uncertain for Sunday night and Monday; however, warming is expected to drive the avalanche danger. Use extra caution on sun-exposed slopes and limit your exposure to large overhead terrain.

Summary

Confidence

Low - Freezing levels are uncertain on Monday

Weather Forecast

Sunday night: 5-25mm of precipitation / Moderate southerly winds / Freezing level at about 2000mMonday: Mainly clear / Moderate to strong southerly winds / Freezing level at about 2000mTuesday: 2-5cm of new snow / Moderate southerly winds / Freezing level at 1700mWednesday: Mix of sun and cloud / Light and variable winds / Freezing level at 2300m

Avalanche Summary

Recent rain, warm temperatures and sunshine initiated numerous loose wet avalanches to Size 1.5 throughout the region. Recent warming and solar radiation also triggered a few deep persistent slabs to size 3 out of steep south facing alpine terrain in the Skeena corridor west of Terrace. Basal facets were thought to be the culprit in these events. Finally, warming was also responsible for a size 2.5 wet slab avalanche that was reported to have failed in the Bear Pass area on Saturday. With precipitation forecast for Sunday night and continued warming on Monday, more loose wet avalanche activity is expected, especially in steep, sun-exposed terrain where cold snow is exposed to solar radiation for the first time. With the forecast warm weather, I'd also consider the possibility of deeper, more destructive slab avalanches.Avalanche and snowpack data is extremely sparse at this time. Please submit your observations to the Mountain Information Network. (MIN)

Snowpack Summary

On Friday and Saturday night about 10mm total precipitation fell 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.

Problems

Loose Wet

With precipitation forecast for Sunday night (and then sun on Monday), I would expect loose wet avalanches to occur, especially in steep, sun-exposed terrain where dry snow is exposed to solar radiation for the first time

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Storm Slabs

At elevations where Sunday night's precipitation falls as snow, dense storm slabs can be expected. Watch for triggering in higher elevation, wind-exposed terrain.

Use ridges or ribs to avoid pockets of wind loaded snow.Use extra caution in lee areas in the alpine and treeline. Storm snow will form touchy slabs.Be alert to conditions that change with elevation.

Aspects: All aspects.

Elevations: Alpine.

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. I'd limit my exposure to large overhead slopes, especially when the sun makes an appearance on Monday.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 11th, 2017 2:00PM