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Avalanche Forecast

Archived

Mar 31st, 2018–Apr 1st, 2018

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

Regions

Sea To Sky.

Caution on shady aspects in the alpine and tree line elevation bands where a persistent weak layer may be reactive. See Friday's Forecaster Blog for more details: goo.gl/8Z83CvAvoid sunny slopes if the sun does come out in full force.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

We're looking at a series of weak weather systems for the next few days. Convective activity could result in locally higher accumulations. Temperatures are staying cool for this time of year. SUNDAY: A mix of sun and cloud with isolated flurries (3-10cm, more possible in the north) / Light to moderate west wind / Alpine temperature -7 / Freezing level decreasing to 1000m MONDAY: Mix of sun and cloud and occasional flurries / Light to moderate southwest wind / Alpine temperature -7 / Freezing level 1000m TUESDAY: Cloudy with flurries / Light to moderate west wind / Alpine temperature -5 / Freezing level 1400m

Avalanche Summary

On Friday a sled-triggered size 2 wind slab was reported near Grizzly Lake near Powder Mountain, on a north west aspect near 1750m. See the MIN post for more details. On Thursday several natural avalanches to size 2.5 were reported in the Tantalus Range. See the MCR for more details. On Wednesday there was a size 1 avalanche that sympathetically triggered a size 3 persistent slab avalanche resulting in a fatality. This was on a northeast aspect at 2000m, 50cm deep. Additionally there were reports of natural persistent slab avalanches size 2.5-3 on southeast through northeast aspects between 1800 and 2000m. These were reported to have happened in the previous 24-48 hours. See this MIN post for similar details.

Snowpack Summary

We've seen only trace amounts of new snow in the past three days. Winds, however, were moderate to strong from the south through to Friday, building fresh wind slabs and further growing cornices.Last week's storm snow was redistributed by moderate to strong southwest winds. This snow rests on the March 21st interface, a mix of moist grains at low elevations, crusts on solar aspects at all elevations and surface hoar/facets on north/east facing features at treeline and alpine elevations. Some west facing features may have surface hoar on top of a crust. The March 21st interface has been giving variably moderate to hard sudden planar results, typically down 50-60cm on 1-2mm facets.Deeper in the snowpack, 80 to 140 cm below the surface is a combination of facets, surface hoar, and/or crust known as the mid-February layer. This interface has not been active recently.The mid and lower snowpack are strong and well settled.

Problems

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.

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.

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.