Avalanche Forecast

Issued: Dec 19th, 2017 3:30PM

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

jfloyer, Avalanche Canada

Northwest Coastal.

Cool and stable weather should mean a gradually strengthening snowpack.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Wednesday: Dry with some clear spells until late in the day. Strong northwesterly winds. Models indicate an inversion will set up for Wednesday afternoon with valley temps around -10C and above-zero between 1400m and 2000m. Thursday: Light snow, 2-5 cm expected, clearing thorough the day. Winds initially strong northwesterly but diminishing through the day. Treeline temps around -8C. Friday: Cold and dry. Moderate and locally strong easterly winds. Treeline temps around -12C.

Avalanche Summary

The north part of the region reported up to size three natural avalanches over the weekend. Poor visibility limited observations in the south but no new avalanches were reported.

Snowpack Summary

The region picked up 20 to 60cm of storm snow over the weekend accompanied by winds out of the southwest, west, northwest, and most recently the east. This will have set up storm slabs in more sheltered areas and wind slabs on a wide variety of aspects in more exposed areas. These new storm and wind slabs may rest on a melt freeze crust (reported to be 3 to 15cm thick), and there are reports there also may be surface hoar resting above this crust in sheltered locations. Below this crust the mid-pack is reported to be generally strong. You can expect to find a second prominent crust, which was buried at the end of October, 100 to 200cm below the surface. This lower layer may have associated facets, particularly in more shallow locations.

Problems

Wind Slabs

20 to 60cm of snow fell during the weekend with wind from the SW, W, NW and SE. As a result, wind slabs on a wide variety of aspects should be expected.

Watch for signs of instability such as whumpfing or cracking.Be alert to conditions that change with elevation, aspect and exposure to wind.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

As recently as this weekend, large avalanches ran on deep persistent weak layers near the base of the snowpack. While it appears to be more likely in the north of the region, the possibility of triggering something big should remain on your radar.

Be especially cautious in areas with a thin or variable snowpack.Storm slabs in motion could step down and trigger deep persistent slab avalanches.Minimize exposure to overhead avalanche terrain, carefully select genuinely safe spots to re-group.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

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