Avalanche Forecast

Issued: Dec 7th, 2017 3:37PM

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

cgarritty, Avalanche Canada

Northwest Inland.

Cooling temperatures should help to stabilize the snowpack, but our lingering persistent slab problem can't be dismissed.

Summary

Confidence

Moderate -

Weather Forecast

Friday: A mix of sun and cloud with thicker valley cloud due to lingering temperature inversion. Moderate to strong southwest winds. Freezing level dropping from 2500 to 2000 metres over the day.Saturday: Cloudy with scattered wet flurries bringing approximately 5 cm of new snow to higher elevations. Light rain below about 1500 metres. Strong southwest winds easing over the day. Freezing level to 2000 metres with alpine temperatures around 0.Sunday: Continuing wet flurries bringing a trace to 5 cm of new snow to high elevations. Light rain below about 1500 metres. Moderate south winds. Freezing level to 2000 metres with alpine temperatures around 0.

Avalanche Summary

No new avalanches have been reported, however it is expected that warm alpine temperatures and sunshine initiated natural activity on steep solar aspects at higher elevations on Thursday. Looking forward, we should see diminishing potential for natural activity until the next storm pulse brings new snow on Saturday.

Snowpack Summary

Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine. (Depths of up to 210 cm have been reported from the Howsons.) Solar and temperature crusts are expected to have formed on the wind-affected surface at higher elevations on Thursday. Below the surface, Approximately 30-50 cm of storm snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although snowpack tests have previously shown hard results at these crust interfaces, more recent observations have been limited. Below these crusts, a well settled midpack overlies the late October crust near the base of the snowpack. This "crust/facet combo" is widespread and has been reactive to rider and remote triggers and has produced recent sudden snowpack test results.

Problems

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 should be on a strengthening trend on Friday, but a heavy trigger in a thin snowpack area may still be enough to cause it to react.

Be especially cautious in shallow snowpack areas where triggering a deeper layer may be easier.Be aware of the possibility for full depth avalanches due to deeply buried weak layers.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Wind Slabs

Older wind slabs exist on a wide range of aspects. Although they are expected to have become quite stubborn, they may still react to heavy triggers in unsupported terrain.

Avoid steep convexities or areas with a thin or variable snowpack.If triggered, wind slabs may step down to deeper layers and result in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 8th, 2017 2:00PM