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Avalanche Forecast

Archived

Jan 15th, 2013–Jan 16th, 2013

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

Regions

Sea To Sky.

Confidence

Good

Weather Forecast

Wednesday: Mostly clear with valley cloud possible in the morning. A temperature inversion is expected to bring treeline and alpine temperatures above freezing, while lower elevations should stay cold. Winds should be light to moderate from the northwest. Thursday: Low cloud in the morning changing to a mix of sun and cloud throughout the day as the temperature inversion weakens and lower elevations start to warm up with freezing levels as high as 2500m. Light to moderate northwesterly winds shifting to westerlies in the afternoon. Friday: A mix of sun and cloud and dry throughout the day. Freezing levels remaining at around 2500m.

Avalanche Summary

There are no new reports or observations of natural or human triggered avalanches in the past 2 days, and I suspect there were a lot of people in the mountains on the weekend. There was a size 2 accidentally triggered slab avalanche in the Spearhead Range on Thursday. A thin wind slab was triggered near ridge top on a relatively low-angle slope, which then stepped down to a weak layer approximately 100 cm deep lower on the slope. This avalanche is suspected to have released on the early January surface hoar layer.

Snowpack Summary

The snow surface consists of thin new wind slabs, a sun crust, moist snow, dry faceted snow, or large surface hoar depending on aspect, elevation, and time of day. Below this 40-70 cm of  recent storm snow sits on a persistent weakness of surface hoar, facetted snow, and/or a crust buried at the beginning of January. Reports from last weekend include a Rutschblock Score of 3 down 52cm on a thin crust in the Whistler area, and hard compression test results on distinct surface hoar on a northeast facing open glade below treeline in the Chehalis (northwest of Hope). No significant weaknesses have been reported recently below this in the mid snowpack layers. Near the base of the snowpack, a crust/facet layer exists, which is now unlikely to be triggered, except perhaps by heavy triggers in steep, shallow, rocky terrain where more facetting has taken place.

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.