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Avalanche Forecast

Archived

Jan 5th, 2021–Jan 6th, 2021

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

Regions

Sea To Sky.

Forecast snowfall combined with strong to extreme wind overnight Tuesday will push avalanche danger to HIGH at upper elevations on Wednesday. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Snow, 15-25 cm, strong to extreme southwest wind, alpine high -4, freezing level 1000 m.

Wednesday: Mainly cloudy with flurries, 5 cm, southwest wind easing to light, alpine high -3, freezing level 1100m.

Thursday: Mainly cloudy, light southwest wind, alpine high -6, freezing level 800m.

Friday: Flurries, 5-10 cm, moderate southerly wind, freezing level 800 m.

Avalanche Summary

Expect an increase in storm and wind slab avalanches on Wednesady with new snow and strong to extreme wind Tuesday night. Reports on Monday and Tuesday show a few explosives controlled storm slab avalanches running size 1-2 as well as a few human triggered storm slab and loose dry avalanches size 1-1.5. 

A large, natural storm slab avalanche cycle size 3-4 occurred near Pemberton over the weekend. Natural and explosive triggered storm slabs size 1-2 were reported elsewhere. This MIN report from Friday illustrates the active avalanche conditions during the weekend storm.

Persistent slab avalanche activity has tapered significantly since the cycle early last week, but persistent slabs size 2-2.5 were still triggerable by explosives on the weekend.

Snowpack Summary

Over 100 cm of recent storm snow has seen extensive wind effect at upper elevations, with scoured windward aspects, wind slabs in lee features and growing cornices at ridgetop.

The snowpack is currently quite complex. The layer of greatest concern is a melt-freeze crust from early December, found around 100-200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. There have been several recent large natural and human triggered avalanches on this layer and new snow loads as well as large loads from storm slab avalanches have potential to trigger these layers.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be especially cautious as you transition into wind affected terrain.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.