Avalanche Forecast

Issued: Apr 18th, 2018 4:21PM

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

jmcbride, Avalanche Canada

Sea To Sky.

Warming and sun are forecasted for Thursday. This combination recently produced large, destructive avalanches on a persistent weak layer. Don't be complacent, these are not typical spring snowpack conditions for this region.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Mostly clear. Ridge wind light, south. Alpine temperature near -4. Freezing level 1000 m.THURSDAY: Mostly sunny, increasing cloud in the afternoon. Ridge wind light, southwest. Alpine temperature near -3. Freezing level 1700 m.FRIDAY: Mostly cloudy, flurries beginning in the evening. Accumulation 5-10 cm. Ridge wind light to moderate, southwest. Alpine temperature near -4. Freezing level 1600 m. SATURADY: Decreasing cloud, flurries ending. Accumulation 2-5 cm. Ridge wind light, west. Alpine temperature near -5. Freezing level 1500 m.

Avalanche Summary

On Monday, small slabs and loose wet avalanches were triggered by skiers and the sun. The slabs were most often 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 during last weekends storm followed by sun and likely on the same weak layer.

Snowpack Summary

About 10-20 cm of new 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. Recent avalanches were triggered during sunny and warm weather, which may occur on Thursday.

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

Loose Wet

The sun packs quite a punch at this time of year. Be cautious when the sun comes out or if you feel warm air temperatures, as this will weaken the snow surface and increase the likelihood of loose wet avalanches.

Use caution above cliffs and terrain traps where small avalanches may have severe consequences.Avoid steep slopes when air temperatures are warm, it is raining, or the solar radiation is strong.Use extra caution on slopes if the snow is moist or wet.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Wind Slabs

Lingering wind slabs exist near ridges. Warming on Thursday may make these slabs easier to trigger. Watch your overhead exposure, as cornice falls could trigger slabs on slopes below.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 19th, 2018 2:00PM