Avalanche Forecast

Issued: Nov 28th, 2017 4:30PM

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

jmcbride, Avalanche Canada

Northwest Inland.

As snow and wind continue to build wind slabs, beware this is also loading a weak layer deep in snowpack. Skiers reported remotely triggering a large avalanche from 200 m away on Tuesday. Be sure to read and post your observations to the MIN.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

WEDNESDAY: Flurries, accumulation 5-10 cm. Strong southwest wind. Alpine temperature -5. Freezing level 1100m.THURSDAY: Flurries, accumulation 5-10 cm. Moderate to strong southwest wind. Alpine temperature -7. Freezing level 700 m.FRIDAY: Flurries, accumulation 5 cm. Moderate gusting to strong southwest wind. Freezing level 700 m.

Avalanche Summary

Skiers in the Seaton area on Tuesday reported remotely triggering a large (Size 2.5) avalanche from 200 m away as they approached a north-facing, treeline bowl at 1650 m elevation. The avalanche was triggered from a shallow snowpack area on the ridgeline and failed on a weak layer of sugary, snow crystals just above the late October crust near the base of the snowpack. Last week several estimated Size 2.5-3 avalanches were observed on the Kathlyn face of Hudson Bay Mountain and are also suspected to have failed on the late October crust. With a layer of sugary crystals above it, this "crust/facet combo" layer is capable of producing very large avalanche and is expected to remain a layer of concern for some time. Please post your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Snowpack depths over the south of the region are above average for late November, with total depths of about 100-120 cm present at treeline elevations and above. Approximately 30-40 cm of recent snow now overlies the supportive November 23 crust that formed as a result of the warm, wet weather and is suspected to extended well into alpine elevations. Below this crust is moist settled snow and the widespread late October crust, which is present near the base of the snowpack at all elevations and features a layer of weak, sugary grains above it. This "crust/facet combo" layer remains an ongoing concern for step-down potential from large triggers such as a storm slab release or, the potential of triggering from shallow snowpack areas. The late October crust is less of a concern below treeline where it is broken up by vegetation near the ground.

Problems

Wind Slabs

New snow and wind continue to build wind slabs in lee areas. Expect these slabs to be more pronounced at higher elevations. Watch for signs of wind affected snow, whumpfing and cracking.

Avoid steep convexities and areas with variable snow distribution.Watch for signs of instability such as whumpfing, hollow drum-like sounds or shooting cracks.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer may react to a heavy trigger like a storm slab release and can also be triggered from shallow snowpack areas.

Be aware of the potential for large avalanches due to weak layers at the base of the snowpack.Be cautious in shallow snowpack areas where triggering a deeper layer may be possible.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Nov 29th, 2017 2:00PM