Avalanche Forecast
Issued: Jan 5th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
MBender,
Avalanche Canada
Forecast snowfall combined with strong to extreme wind overnight Tuesday will push avalanche danger to HIGH at upper elevations on Wednesday.
Summary
Confidence
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
Overnight snowfall combined with wind has likely created widespread and reactive storm slabs. Forecast strong to extreme southwest wind has likely created deep deposits in exposed lee terrain.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A couple of problematic layers may be found around 100 to 200 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. These layers have shown a downtrend in activity since early last week but there remains potential for avalanches to step down to these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 6th, 2021 4:00PM
