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Avalanche Forecast

Archived

Jan 11th, 2022–Jan 12th, 2022

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
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.

Avoid avalanche terrain throughout this storm. Deeply buried weak layers are likely to produce large and destructive natural avalanches. 

Storm slabs will build at higher elevations, while rain and warm temperatures saturate the snowpack at lower elevations.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

The storm continues, a more intense front moves over the region bringing heavy rain and wind.

TUESDAY NIGHT: Rain begins overnight, delivering 20-45 mm below freezing levels at 2000 m, with mixed precipitation and snow above. Strong southwest winds continue.

WEDNESDAY: Freezing levels remain at 2000 m for the day, 20-50 cm expected over the day above the freezing level and heavy rain below. 

 

THURSDAY: The front exits leaving clearing skies and light precipitation expected. Freezing levels sit around 1500 m, with light easterly winds. 

FRIDAY: Partly cloudy with no precipitation expected. Winds return to strong southwest. Freezing levels at 1500 m. 

Avalanche Summary

A widespread natural avalanche cycle is expected to occur at all elevations with the heavy rain, snow and wind with rising temperatures over Tuesday and Wednesday. 

A natural slab avalanche cycle was observed near Squamish on Sunday. Avalanches were observed to size 3 on all aspects below treeline, and south facing aspects at treeline. 

A size 2.5 naturally triggered slab avalanche was reported near Whistler, thought to have failed on the early December crust/facet combination. Small storm avalanches may step down to deeply buried weak layers such as this. 

Snowpack Summary

30-60 cm of mixed precipitation has created a variety of surface snow conditions. Strong southwest winds have created deeper deposits at treeline and alpine elevations on north through east facing slopes. At lower elevations the precipitation fell as rain creating a saturated upper snowpack sitting over a melt freeze crust observed to 2000 m.

This recent precipitation adds to the 100+ cm of snow that has fallen since January 1, which may overly sugary faceted grains that formed during the cold spell in late December.

Around 150 to 250 cm deep, another weak layer of faceted grains may be found above a melt-freeze crust that formed in early December. The layer is most prominent between 1700 and 2100 m. Avalanches on this layer are large, but sporadic and isolated. The most likely place to trigger it would be in thin, rocky snowpack areas. The lower snowpack is well-settled and strong.

Terrain and Travel

  • Minimize exposure during periods of heavy loading from new snow, wind or rain.
  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.