Avalanche Forecast

Archived

Feb 25th, 2021–Feb 26th, 2021

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Regions

Northwest Coastal.

Travel in avalanche terrain is not recommended even if natural avalanche activity tapers off, it is likely that new storm slabs will be very reactive and primed for skier and rider triggers. Fresh and reactive wind slabs will likely build throughout the day.

Confidence

High - Uncertainty is due to the extreme variability of wind effect on the snowpack. We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

Friday: A mix of sun and cloud with alpine temperatures near -5. Ridgetop wind strong from the northwest. Freezing level valley bottom.

Saturday: Snow 10-15 cm. Alpine temperatures near -8. Ridgetop wind strong from the southwest and freezing level 600 m.

Sunday: Snow 20-50 cm. Alpine temperatures near -3 and ridgetop wind strong to extreme from the southwest. Freezing level 900 m.

Avalanche Summary

By Thursday afternoon no new avalanches were reported. However, I suspect reports will come in Thursday night and a natural avalanche cycle likely occurred.

More evidence of the avalanche cycle up to size 3.5 from earlier this week was observed as the skies cleared. For example, check out this MIN near Shames. This MIN shows excellent photos of slab avalanches around treeline elevations, potentially releasing on the surface hoar described in the Snowpack Summary.

Looking towards Friday, natural avalanches may taper but skier and rider triggering are likely. Fresh wind slabs may also form throughout bthe day and be reactive.

Snowpack Summary

Near 50 cm of new snow accumulated by Thursday mid-day in most parts of the region. The region may see anywhere from 20 to 40 cm by Thursday afternoon above 800 m, with associated strong to extreme southwest to northwest wind. Storm slabs are expected to build rapidly in sheltered terrain and wind slabs in exposed terrain at high elevations. Below 800 m, rain will soak a snowpack that was recently wet.

This snow will add to the 100 cm of snow that fell on the weekend, which may not be bonding well to previous surfaces buried mid-February, including:

Hard wind-affected snow, particularly in exposed alpine and treeline terrain,
Weak and feathery surface hoar in sheltered areas, with the most suspect elevation bands being lower alpine, treeline, and within openings below treeline,
A 20 to 40 cm thick layer of sugary faceted grains that developed during cold periods, and/or
A hard melt-freeze crust below treeline.

The mid-pack has been reported as being well-settled. There are presently no deeper concerns.

Terrain and Travel

Keep in mind that human triggering potential persists as natural avalanching tapers off.
Travel in alpine terrain is not recommended.
Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
Avoid the runout zones of avalanche paths. Avalanches could run full path.
Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.