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Avalanche Forecast

Archived

Feb 16th, 2020–Feb 17th, 2020

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

Northwest Inland.

Start small and aim for areas that haven't been exposed to recent winds. The possibility for large persistent slab avalanches from suspect terrain features should factor into your terrain decisions.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Sunday night: Cloudy with scattered flurries bringing up to 10 cm of new snow. Strong northwest winds. Alpine low -10 C. Freezing level valley bottom.

Monday: Mainly cloudy. Strong west winds, easing over the day. Alpine high temperatures around -8 C.

Tuesday: Mix of sun and cloud. Light southwest winds. Alpine high temperatures around -4 C.

Wednesday: Mix of sun and cloud. Moderate southwest winds, strong at ridgetop. Alpine high temperatures around -4 C.

Avalanche Summary

Reports from Saturday consisted of several human triggered storm slabs size 1-1.5 at treeline and below and a few natural (possibly cornice-triggered) slabs on north to east aspects in steep open bowls at treeline.

Reports from Friday included an observation of a large cornice-triggered wind slab in Morning Bowl - see the report here. 

During the first half of the month there were many very large and destructive avalanches failing on deeply buried weak layers near the bottom of the snowpack. The bulk of this activity occurred above treeline on north through east facing aspects, but any large alpine slopes that have not yet avalanched should be treated as suspect. A few examples of MIN reports of large events February 8-11 include Hudson Bay, Kathlyn Face, French Peak, Pine Creek Trail, and Babines.

Snowpack Summary

10-40 cm of new snow fell over the last week with greatest accumulations in the west of the region. In exposed areas, this snow is highly wind affected. At lower elevations, the recent snow overlies isolated patches of surface hoar in shady sheltered areas or crusts on south-facing slopes and below 1200 m.

A weak layer of faceted snow that formed during cold weather in mid January is buried approximately 60-120 cm below the surface. A few large avalanches were triggered on this layer in the first half of the month.

An older crust/facet layer from November, lurking at the base of the snowpack, produced many very large avalanches during the first half of the month. As a product of old, weak snow from the early season, this layer is most likely to be found at high elevations.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

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.

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.