Avalanche Forecast

Issued: Dec 19th, 2017 3:23PM

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

jfloyer, Avalanche Canada

Northwest Inland.

While conditions are generally good, extra caution is warranted in windy areas and around convoluted rocky areas with a shallow snowpack.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

Wednesday: Dry with some clear spells until late in the day. Strong northwesterly winds. Models indicate a weak inversion may set up for Wednesday afternoon with valley temps around -12C and alpine temps more like -5C. Thursday: Light snow, 2-4 cm expected, clearing thorough the day. Winds remaining strong northwesterly. Treeline temps around -12C. Friday: Cold and dry. Light easterly winds. Treeline temps around -20C.

Avalanche Summary

Some natural and skier-triggered avalanche activity was noted from the weekend - it appears as though it can be characterized as small wind slab activity. If you're out in the mountains and see recent avalanches please snap a photo and submit your information to the Mountain Information Network.

Snowpack Summary

The inland region picked up 5 to 15cm of new snow over the weekend accompanied by wind that was initially out of the west, but has since switched to being out of the southeast. This new snow rests on a wide variety of old surfaces including small facets, crusts on solar aspects and stubborn old wind slabs near ridge crest. In protected areas below 1500m the new snow may be sitting on previously formed feathery surface hoar.Two crusts formed near the end of November are found approximately 30 to 50cm below the surface. These crusts are widespread and extend into the alpine. Previous snowpack tests produced hard results on these crusts, but we have not seen any recent information about their sensitivity to triggering. Below these crusts, a well settled mid-pack overlies the late October crust which is down near the ground. The October crust is widespread and has not been reactive to human triggering since the end of November. Average snowpack depths in the region are between 80 and 140cm at treeline, with up to 160cm in the alpine.

Problems

Wind Slabs

Wind slabs are most likely to be found immediately lee of ridge crest and around mid-slope terrain features like rock outcroppings. While relatively small, they could be problematic in complex terrain.

Avoid steep convexities or areas with a thin or variable snowpack.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack and while it should be gaining strength a heavy trigger in a thin rocky terrain feature may still be able to initiate a failure and subsequent large avalanche.

Be aware of the possibility for full depth avalanches due to deeply buried weak layers.Be especially cautious in shallow snowpack areas, it may be possible to trigger large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 20th, 2017 2:00PM