Avalanche Forecast
Issued: Feb 3rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
swerner,
Avalanche Canada
Natural avalanche activity will likely taper but slabs remain primed for skier and rider triggering. Conservative terrain choices are a great way to handle a persistent slab avalanche problem.
Summary
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.
Weather Forecast
Thursday: Cloudy with some flurries 3-5 cm. Alpine temperatures near -7 and freezing levels at the valley bottom. Ridgetop winds are strong from the southwest.
Friday: Mix of sun and cloud. Alpine temperatures are low of -20 and high of -5 with strong ridgetop wind from the West.
Saturday: Mix of sun and cloud with snow up to 5 cm. Alpine temperatures low -22 and high -15. Ridgetop wind light from the West.
Avalanche Summary
On Wednesday, numerous natural storm slab avalanches were reported up to size 2, and several more slabs were triggered by explosives up to size 1.5. Loose dry avalanches were seen up to size 1. On Tuesday, a widespread natural avalanche cycle occurred up to size 2.5.Â
Last weekend numerous persistent slab avalanches were reported up to size 1.5 primarily on NE aspects above 1700 m. These avalanches were easily triggered by the weight of a human either directly or remotely (from a distance away). Check out these reports that show how reactive the slab is: MIN Report, MIN report, or this MIN report.Â
As natural avalanche activity tapers, wind and persistent slabs may still be primed for triggering on Thusday.
Snowpack Summary
Up to 60 cm of recent snow has formed a cohesive and reactive slab that sits above a weak interface of surface hoar and surface facets (weak sugar or feather-like snow crystals) and a crust. In the alpine, this slab of recent snow sits on top of a plethora of old snow surfaces comprising of hard wind slab, scoured areas, sastrugi, and isolated pockets of soft snow. Below 1800 m a hard melt-freeze crust underneath the new snow is found and a surface crust now exists up to 1700 m from the high freezing levels on Tuesday.
A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which are currently unreactive.Â
Terrain and Travel
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
- Avoid terrain traps where the consequence of any avalanche could be serious.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Persistent Slabs
A cohesive slab 30-60 cm thick now sits above a buried weak layer of surface hoar, surface facets and crust. These slabs have been very reactive to human triggers showing wide propagations in moderate to low angle terrain. They have been catching people by surprise, so pay attention to signs of instability and stay clear of terrain traps like creeks, cliffs, and depressions below you.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Moderate wind from the west-northwest has redistributed recent storm snow to leeward slopes and terrain features building fresh wind slabs.
Cornices are large and fragile and don't respond well to rapid change- like new load from snow, rapid warming or rapid cooling. They deserve respect and a wide berth from above and below.
Aspects: North, North East, East, South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 4th, 2021 4:00PM
