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Avalanche Forecast

Archived

Jan 20th, 2022–Jan 21st, 2022

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

Major warming and sun are expected to destabilize the snowpack over the next few days. The recent storm snow is expected to be reactive on Friday, cornices will start to weaken, and deep weak layers may begin to wake up. Wet loose activity is expected on steep sun exposed slopes.

Confidence

Moderate - Uncertainty is due to rapidly fluctuating freezing levels. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A warm ridge of high pressure establishes itself over the region on Friday and is expected to bring sustained freezing levels around 3000 m with an inversion for the weekend. 

Thursday Night: Skies clearing overnight, light to moderate NW wind, freezing levels 1200-1400 m. 

Friday: Mainly sunny, light to moderate NW wind, freezing levels climbing to around 3000 m with an inversion. 

Saturday: A mix of sun and cloud, light NW wind, freezing levels around 3200 m with an inversion. 

Sunday: A mix of sun and cloud, light to moderate W wind, freezing levels around 3000 m dropping to around 2000 m by the end of the day. 

Avalanche Summary

On Tuesday, explosives triggered three large cornices, none of which triggered slabs on the slopes below. Just north of the region on Tuesday, two human-triggered size 1-1.5 wind slabs were reported on NW-NE aspects at 1950 m. On Monday, a natural size 2 storm slab was reported on a SW aspect around 1800 m. 

Snowpack Summary

At higher elevations, the recent storm snow has buried the widespread January 16 melt-freeze crust which extends to around 2100 m. There have also been some observations of surface hoar sitting on the crust north of Pemberton but this does not appear to be widespread. This surface hoar was observed on polar aspects at treeline and in the alpine. The most recent storm snow is expected to have formed reactive storm slabs in wind exposed high elevation terrain. Storm slabs may become more reactive and widespread on Friday as the recent storm snow settles rapidly with the warming. At lower elevations, the upper snowpack is moist or wet from the recent rain event. 

The depth of the early December crust/facet layer is highly variable through the region but appears to be typically down 100-200 cm. Some operators are showing the depth as low as 60 cm in shallow snowpack areas and as deep as 3 m in wind loaded terrain. The weak layer is most prominent between 1700 and 2100 m. The layer has been dormant recently but is a concern for the period of major warming and sun forecast for the weekend. The most likely place to trigger it would be in thin, rocky snowpack areas where it is shallowest. 

Terrain and Travel

  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Be alert to conditions that change with elevation and wind exposure.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.