Avalanche Forecast

Issued: Apr 19th, 2018 4:30PM

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

jmcbride, Avalanche Canada

Sea To Sky.

A buried weak layer at treeline and above remains a concern, as well as pockets of wind slab in high, northerly terrain. Also be wary of sunny slopes and cornices should the sun make an appearance.

Summary

Confidence

Moderate -

Weather Forecast

TONIGHT: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, southwest. Alpine temperature near -5. Freezing level 1100 m.FRIDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind light to moderate, south. Alpine temperature near -5. Freezing level 1500 m. SATURADY: Mostly cloudy, flurries ending. Accumulation 10-15 cm (up to 20 cm near Squamish). Ridge wind moderate, west. Alpine temperature near -5. Freezing level 1500 m.SUNDAY: Sunny. Ridge wind light, north. Alpine temperature near -2. Freezing level 1800 m.

Avalanche Summary

Wednesday a skier accidentally triggered a storm slab avalanche (size 1.5) on a steep, east aspect at 2600 m that released on a crust 30 cm deep. Explosive control work in the ranges west of the Pemberton Icefield produced size 3 persistent slab avalanches that are suspected to have failed on the late March weak layer. Observations of older, natural size 3-3.5 avalanches in the area where also attributed to this persistent weak layer. And older natural size 3-3.5 avalanches were also observed at 1800-2100 m in the McBride range.On Monday, small slabs and loose wet avalanches were triggered by skiers and the sun. Slabs were reactive in lee terrain features near ridges.On Sunday, a large (size 3) persistent slab avalanche was remotely triggered by a snowmobile on a north aspect in alpine terrain with substantial air temperature and solar warming over the day. The avalanche likely released on the late March weak layer. Also on Sunday a large avalanche was observed close to Whistler, on a north aspect around 2000 m, with a depth of about 1 m. It was suspected to have released with sun following last weekends storm, and likely on the same weak layer.

Snowpack Summary

About 10-30 cm of recent snow has been redistributed by strong northwesterly winds. This overlies variable surfaces, including old wind slabs at high elevations, and crusts on most aspects. A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is most likely to be problematic on west, north, and east aspects between 1900 m and 2250 m. Professionals are treating this layer very cautiously and avoiding terrain because of it. Read Conditions report here.The mid and lower snowpack are well-settled and strong.

Problems

Persistent Slabs

Professionals are traveling cautiously due to a weak layer buried 60 to 140 cm. The layer is found in upper treeline and alpine terrain on shady aspects. Warming and cornice failures have been triggers for recent avalanches on this layer.

Avoid steep terrain or areas with a thin or variable snowpack.Be aware of the potential for wide propagation due to the presence of buried weak layers.Pay attention to overhead hazards like cornices, which could trigger persistent slabs.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Lingering wind slabs may still exist in alpine northerly terrain near ridge crests.

Caution in lee and cross-loaded terrain near ridge crests.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Loose Wet

The sun packs quite a punch at this time of year. Be cautious if the sun comes out or if you feel warm air temperatures. This can weaken the snow surface and increase the likelihood of loose wet avalanches especially on steep sunny aspects.

Use extra caution on slopes if the snow is moist or wet.Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Aspects: North, North East, East, South East, South.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Apr 20th, 2018 2:00PM