Avalanche Forecast
Issued: Dec 25th, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
cmortenson,
Avalanche Canada
Recent snow & winds are creating reactive wind slabs. There are also buried weak layers. Large and destructive avalanches may be triggered by a person in steep or convex terrain. Continue to make conservative terrain choices as you safely enjoy your holidays.
Summary
Confidence
Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to how quickly the snowpack will recover and gain strength.
Weather Forecast
A weak weather system will bring light snow, moderate west/southwes winds and cool temps for the weekend ahead of a building high pressure system.
Friday night: Mainly cloudy with scattered flurries trace-5cm new snow. Alpine low temperatures near -7 and freezing levels valley bottom. Ridgetop wind light to moderate from the west / southwest.
Saturday: Cloudy with scattered flurries trace-5cm new snow. Alpine high temperatures near -7 and freezing levels valley bottom. Ridgetop wind light to moderate from the west / northwest.
Sunday: Cloudy with sun breaks and isolated flurries. Alpine high temperatures near -7 and freezing levels valley bottom. Ridgetop wind light and variable gusting moderate.
Monday: Mix of sun and cloud. Alpine high temperatures near -9 and freezing levels valley bottom. Ridgetop wind light and variable west.
Avalanche Summary
No new reports on Friday at the time of publishing, however the snowpack is still recovering from the recent storm which triggered a widespread avalanche cycle mid-week up to size 3. Natural avalanche activity may taper off a bit but the snowpack remains primed for human triggering, especially in periods of active wind-transport.
On Thursday there were a few explosive triggered size 1 avalanches were reported and large explosive controlled avalanches from nearby regions.
On Wednesday numerous storm slabs up to size 1.5 were triggered with explosives. This MIN from Tunnel creek also reports numerous large avalanches on cross loaded features at treeline.
On Tuesday, a widespread natural avalanche cycle up to size 3 was reported from the lizard range with many avalanches reported from northerly aspects.Â
Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter!
Snowpack Summary
30-60 cm of recent snow blanketed the region by Tuesday morning and has been blown by moderate to strong winds in exposed treeline and above since then. Moderate to strong west and southwestern winds created significant ridgetop snow re-distribution onto lee slopes. Wind slabs will likely remain reactive to human triggers, and are the most reactive during periods of moderate to strong winds. Cornice development may be found along ridgecrests and deep windslabs on lee slopes.Â
Recent snow fell on a variety of old surfaces including a buried melt-freeze crust reported below 1700m and surface hoar reported around treeline. This MIN has some great photos and snow tests that show new snow (10-20cm) is not bonding well to this recent rain crust.Â
A persistent slab 70-130 cm thick now sits on the early December crust. This persistent weak layer, with facetted crystals and surface hoar crystals above and/or below it is reaching a tipping point. Deeper in the snowpack are two hard melt-freeze crusts that formed in November that may have some weak crystals around them. This potential avalanche problem is dormant at this time, however; it remains on our radar.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
- Don't let the desire for deep powder pull you into high consequence terrain.
- Minimize your exposure time below cornices.
Problems
Wind Slabs
Natural avalanche activity may taper off a bit with the end of the snowfall, but moderate to strong west/southwest winds are creating fresh windslabs on lee slopes making the snowpack primed for human triggering. These may be touchy during periods of active wind transport. Be on the look-out for cornice formation: these are a hazard underfoot as well as being an overhead hazard that is capable of triggering large avalanches should they fail.
Loose-dry sluffing from sheltered steep terrain is likely, especilly when the sun comes out.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
This layer reached a tipping point with recent new snow as evidenced by the recent natural avalanche cycle. Although naturally triggered avalanches have tapered, it remains possible to tigger this layer in thin to fat zones, with a step-down avalanche or on slopes that have received significant wind transport. Depending on elevation and aspect, 80-150 cm of snow currently sits above a buried crust from early December. Sugary, facets and surface hoar around the crust mean persistent slabs are likely reactive, especially to human triggers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 26th, 2020 5:00PM
