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Avalanche Forecast

Archived

Apr 19th, 2018–Apr 20th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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.

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

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.