Avalanche Forecast
Issued: Jan 17th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
ahanna,
Avalanche Canada
Low elevation trees are your best chance at avoiding windslabs and finding soft snow and reasonable temperatures on Saturday.
Summary
Confidence
Weather Forecast
Friday night: Increasing cloud with flurries starting, trace accumulations. Wind building to strong south to southeast. Alpine temperatures around -25 C.
Saturday: Mostly cloudy with flurries bringing 5-10 cm of new snow. Strong southeast to southwest winds. Alpine high around -18 C.
Sunday: Mix of sun and cloud with isolated flurries bringing up to 5 cm of new snow. Moderate south to southwest winds, strong at ridgetop. Alpine high around -15 C.
Monday: Mix of sun and cloud with isolated flurries bringing up to 5 cm of new snow. Light to moderate southeast winds.. Alpine high around -10 C.
Avalanche Summary
On Wednesday and Thursday, we received reports of skier triggered windslab avalanches size 1.5-2.5 around treeline. Crown depths were up to 1 m, and they ran on a surface hoar layer buried by the previous storm on January 10th.
Reports from the Bulkley Valley Monday detail natural windslab and persistent slab avalanche activity, size 2.5-3 on aspects lee to previous strong outflow winds. The persistent slab avalanches are suspected to be isolated incidents of avalanches running on the deep November crust.
Snowpack Summary
Extensive wind affect at all elevations. Southerly winds are forming fresh windslabs from new snow in places that were previously scoured by northeasterly arctic outflows.
Around treeline, the old windslabs may overly a layer of surface hoar, up to 1 m deep. This means they may remain sensitive to human triggering and resulting avalanches could be surprisingly large. Deeper in the snowpack, another couple of surface hoar layers are currently buried about 80-120 cm below the surface in sheltered areas around treeline. There have been no reports of avalanche activity associated with them for a few weeks, during which several storm slab avalanche cycles have tested their potential for step-downs.
A deep crust from mid November lurks at the base of the snowpack. A couple of recent large avalanches are suspected to have run on this layer in isolated incidents on lee and cross-loaded features high in the alpine.
Terrain and Travel
- Recent new snow may be hiding windslabs that were easily visible before the snow fell.
- Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Wind slabs are most reactive during their formation.
- Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
Problems
Wind Slabs
A bit of new snow amid strong winds will form fresh wind loaded pockets at alpine and treeline in features lee to southerly flow. Where previous northeast outflows formed windslabs over surface hoar, these old windslabs may remain sensitive and may exceed 1 m in depth.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A deep crust from mid November lurks at the base of the snowpack. There is uncertainty around its prevalence as an active avalanche problem as opposed to isolated incidents of large naturals in lee or cross loaded extreme alpine terrain. Human or even vehicle triggering at this depth is difficult, but can occur from shallow, rocky areas and propagate out to where the snow is deeper. If triggered these are very large, high consequence avalanches.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Jan 18th, 2020 5:00PM
