Above 2,500ft Moderate
1,500 to 2,500ft Moderate
Below 1,500ft Low
Degrees of Avalanche Danger ?
Problem #1: Wind Slab
16-32″ of snow fell last week above 2,000ft (highest amounts in the Lutak zone, less at the Pass). This new snowfall fell upside-down: cold and weak underneath with a heavy cohesive slab on top. It sits atop a variable surface of crusts, hard slab, and patches of surface hoar. It has since been whipped around by both south and north winds, so expect to find multiple layers of wind slab on any aspect. Beneath and between the slabs, there remain softer weak layers that will be prone to failure, especially on steep, convex, or unsupported slopes. If you dig a pit to evaluate a slope, make sure it is representative of what you plan to ride down. Keep in mind the high variability that exists from slope to slope and at different point within a run. If you choose to ride in avalanche terrain, have a plan for what to do if you trigger a wind slab, with escape routes and safe zones. Human-triggers are still possible within these upper wind slabs, despite multiple days of bonding since Saturday. Finally, we have had multiple reports of clean shears around 80cm deep in snowpits. It will be hard to trigger this layer in the field, but smaller slides could step down this deep. Keep in mind this elevated risk for deeper slides.
Problem #2: Deep Slab
We still have 2-4mm depth hoar at the ground, beneath a hard midpack. In late December several slides ran on this layer as a heavy load of new precipitation placed strain on it. Triggering this deep layer will be difficult, but still possible. This is especially true in thin/rocky areas which will act as trigger points, and may cause remote triggering and wide propagation. The best way to manage this danger is to stick to areas with a deeper snowpack, make sure your safe areas are well-outside the danger zone, and include a wide safety margin. Careful group management is crucial right now, as any slides that break this deep could be large, and break wider than expected.
Recent Avalanche Activity
Recent reports are mainly of settling/whumphing within the new storm snow from the weekend. There was one small skier triggered slide that was a remote trigger (Propagated a distance out from where the skier was riding and triggered an avalanche at a distance). These reports are from Friday-Sunday.
We can expect one more nice day (Thursday) before the next storm cycle begins on Friday. 6-12″ of new snow is likely Friday-Friday night, with a heavier, warmer storm on tap Saturday night.
|Snow Depth [in]||Last 24-hr Snow/SWE [in]||Last 3-days Snow/SWE [in]||Today’s Freezing Level [ft]||Today’s Winds||Next 24-hr Snow/SWE|
Mount Ripinsky @ treeline
|37″*||0″ / 0.00*||0″ / 0.00||0||mod, N||0″/ 0.00 *|
Flower Mountain @ treeline
|32″||0″ / 0.00||0″ / 0.00||0||mod, NW||0″ / 0.00 *|
Chilkat Pass @ 3,500ft
|20″||0″ / 0.00 *||0″ / 0.00 *||0||mod, NW||0″ / 0.00 *|
( *star means meteorological estimate )
Additional Info & Media
A few notes:
- We had an extremely dry, cold early-season. Total precipitation October 1st – November 28th was around 30% of normal. Snow depths are between 45-130cm in most areas. Variability is high due to persistent dry, windy conditions.
- Temperatures hovered around 0 – 15°F for almost all of November. This has caused faceting of the thin snowpack and built up 3-5mm depth hoar at the ground in all zones.
If you get out on the snow, send in your observations!
We will be providing an AIARE Avalanche Level 1 Class this winter in Haines, February 23-25, 2018