Avalanche Forecast

Issued: Apr 18th, 2018 4:24PM

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

jmcbride, Avalanche Canada

South Coast Inland.

Warming and sun on Thursday will increase the likelihood of avalanches. Be very wary of the persistent weak layer in the snowpack in the north of the 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. Ridge wind light to moderate, southwest. Alpine temperature near -3. Freezing level 1800 m.FRIDAY: Mostly cloudy, flurries beginning overnight. Accumulation 2-5 cm. Ridge wind light to moderate southwest. Alpine temperature near -3. Freezing level 1700 m. SATURDAY: Mix of sun and cloud, light flurries. Accumulation 2-5 cm. Ridge wind strong, southwest. Alpine temperature near -4. Freezing level 1600 m.

Avalanche Summary

Explosive control work in the Duffey Lake area on Wednesday produced a size 3 persistent slab avalanche that propagated over 200 m wide, failing on the late March weak layer. This result was on a west to southwest aspect between 2100-2200 m.Tuesday there was a report skier's remotely (from a distance) triggering a a size 2 wind slab on a steep east aspect in the Duffey Lake area. Read more details here.On Monday, a large slab avalanche was noted in Duffey Lake Road region in alpine terrain. It was likely triggered by a cornice fall during sunny and warm conditions. The slab likely failed on the late March weak layer. Whumphing and cracking (10-20 cm deep) were also noted at ridgetop. Large (size 3) persistent slab avalanches were observed in the far north of the region over the weekend. They were about 60 to 80 cm deep, on northwest to east aspects, between 1800 and 2200 m, and failed naturally on the weak late March surface hoar layer. These propagated widely across the slopes. Many slides in the recent storm snow were also observed, often triggered by cornice failures.

Snowpack Summary

20 to 40 cm of new snow (highest amounts near Coquihalla Highway) has been redistributed into lee terrain features from northeast switching to southwest winds. This overlies variable surfaces, including wind slabs at high elevations, and crusts on all aspects up to at least 2000 m, and possibly higher on south aspects.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 50 to 100 cm. This layer is spotty in its distribution and has recently produced large and destructive avalanches. It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.The mid and lower snowpack are well-settled and strong.

Problems

Storm Slabs

Recent snow may not bond well to an underlying crust. Slabs have been most reactive adjacent to ridges in wind-loaded terrain. Watch your overhead exposure, as cornices could trigger slabs on slopes below.

Avoid steep slopes when air temperatures are warm or solar radiation is strong.Use caution in lee areas. Wind loading and warming has created reactive slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

Professionals are traveling cautiously due to a weak layer buried 50 to 100 cm. The layer is found in upper treeline and alpine terrain on shady aspects. Recent large avalanches have been reported in the north of the region 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 convexities or areas with a thin or variable snowpack.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

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 triggering avalanches.

Avoid steep slopes when air temperatures are warm, or solar radiation is strong.Use extra caution on slopes if the snow is moist or wet.If triggered the loose wet sluffs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

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