Avalanche Forecast

Issued: Apr 20th, 2018 4:09PM

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

jlammers, Avalanche Canada

Sea To Sky.

Forecast snowfall amounts are extremely variable throughout the region. Pay close attention to how much snow falls in your riding area and be prepared to back-off to simple terrain.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

Friday night and Saturday: 15-30cm of new snow / Strong to extreme southwest winds / Freezing level at 1300mSunday: Clear skies / Light and variable winds / Freezing level at 1900mMonday: Clear skies / Light and variable winds / Freezing level at 2400m

Avalanche Summary

On Wednesday explosives 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. Older natural size 3-3.5 avalanches were also observed at 1800-2100 m in the McBride range. I would expect intermittent persistent slab activity with warming and solar radiation forecast for Sunday and Monday. In the short term, new snow and wind will promote new wind slab activity on Saturday.

Snowpack Summary

New snow and wind on Saturday are expected to form fresh wind slabs in upper elevation lee terrain. The new snow is expected to overlie settled storm snow on shaded aspects above 2000m and a melt-freeze crust in most other areas.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 below the surface. 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 steep, unsupported terrain. Read Conditions report here.The mid and lower snowpack are well-settled and strong.

Problems

Wind Slabs

New snow and wind will promote new wind slab development in upper elevation lee terrain. Watch for triggering behind ridge crests and in gullies.

Be cautious as you transition into wind affected terrain.Stay off recent wind loaded areas until the slope has had a chance to stabilize.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

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.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Apr 21st, 2018 2:00PM