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Avalanche Forecast

Archived

Dec 21st, 2018–Dec 22nd, 2018

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

Regions

South Coast Inland.

Recent slabs formed at high elevations may still be reactive to human traffic, especially in lee terrain features. For the north of the region, be diligent around treeline where a buried weak layer may still linger.

Confidence

Moderate.

Weather Forecast

FRIDAY NIGHT: Mostly cloudy, freezing level below valley bottom. SATURDAY: Cloudy with light snowfall, accumulation 5cm, moderate southwest winds, alpine temperature -7°c, freezing level below valley bottom. SUNDAY: Cloudy with snowfall, accumulation 5 to 10cm, moderate southwest winds, alpine temperature -5°c, freezing level 600m. MONDAY: Clearing over the day, light south winds, alpine temperature -8°c, freezing level 800m.

Avalanche Summary

A natural storm slab avalanche cycles occurred on Thursday in the north of the region, with large avalanches up to size 3. This is similar to cycles that occurred during previous storms within the past week (see description and photos here). Few avalanches were observed in the south of the region on Thursday.

Snowpack Summary

Around 30 to 40 cm of snow fell in the region on Thursday at high elevations. Below about 1800 m expect to find a melt-freeze crust due to rain. At high elevations, expect to find deeper slabs in the lees of terrain features due to strong variable winds. In the north portion of the region and possibly the far south, a weak layer of facets and surface hoar lies below all this storm snow, around 120 cm deep. The weak layer appears most prominent around treeline, up to 2000 m. While the layer is likely gaining strength, field observations show that slab avalanches remain possible on this layer where it exists. Near the base of the snowpack, a crust exists with weak and sugary facets beneath it. This could potentially still be of concern in high north-facing aspects where the snowpack rests on very smooth ground cover.

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.