We will be providing an AIARE Avalanche Level 1 Class this winter in Haines, February 23-25, 2018
Above 2,500ft Considerable
1,500 to 2,500ft Considerable
Below 1,500ft None
Degrees of Avalanche Danger ?
Above treeline, human-triggered avalanches are possible on any slope steeper than 25 degrees, but most likely on wind loaded slopes, convexities, and steep gullies. Below treeline, human triggering is likely in open areas steeper than 30 degrees.
The main concern will be new storm snow and wind slabs from last week that sit at the top of the snowpack. These slabs (10-50cm thick) are cold, brittle, and tender, sitting on a layer of weak facets.
Our current alpine snowpack is characterized thus: 3-5mm depth hoar at the ground, with a pencil-hard rain crust above, and varying cold wind-packed layers above that. The upper slab has been tender and reactive, sliding on planar crystals and facets above the ice crust. Variability is high, so be sure to evaluate each slope, and leave a wide safety margin.
The takeaway: our snowpack is thin, highly variable from place to place, and generally weak with poor structure.
A few notes:
- Avalanche season is here. We’ve already had a significant skier-triggered avalanche reported (see below).
- We have an extreme lack of snow so far this season. Total precipitation since October 1st is at 38% of normal. Snow depths are around 10cm at 3,500ft, ranging up to 100cm in wind loaded areas above 5,000ft. Variability is high due to persistent dry, windy conditions.
- Temperatures above treeline have been around 0 – 5°F. This has caused faceting of the thin snowpack and built up 3-5mm depth hoar. This will be a weak base to hold up future heavy snows. Keep this in mind as November progresses and snow depths increase. This will likely turn into a deep-persistent slab problem.
Start the season with fresh batteries in your beacon, and practice with your beacon, shovel, and probe.
If you get out on the snow, send in your observations!
Recent Avalanche Activity
October 28th: First rider-triggered slide reported from the peak north of Nadahini (“Sunny Bunny”). D2 soft slab ran in storm snow from Oct 26-27. Nobody caught or injured. [ SS-AR-D2-R3-S ] South aspect @ 6,200ft.
Small – Moderate natural avalanche activity is occurring during/after storms. So far it has been mostly loose-snow slides, with a few slab avalanches as well.
Alpine temperatures have been (5 – 15°F) for the last 3+ weeks. Northwest winds have been moderate-strong with occasional blowing snow. Sunday should bring clearing, before the next storm on Monday brings moderate accumulations and a warming trend for the week ahead.
|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
|5″ / 0.30||18″ / 1.05||0||strong, NW||0″ / 0.00 *|
Flower Mountain @ treeline
|5″ / 0.30||11″ / 0.60||0||strong, NW||0″ / 0.00 *|
Chilkat Pass @ 3,500ft
|10″ *||3″ / 0.15 *||8″ / 0.40||0||strong, NW||0″ / 0.00 *|
( *star means meteorological estimate )