Caution advised in glacier areas: this year’s alpine snowpack is thinner than normal and our glaciers are more likely to have thin snow bridges over crevasses.
Above 2,500ft Considerable
1,500 to 2,500ft Moderate
Below 1,500ft Low
Degrees of Avalanche Danger ?
Underneath last night’s new snow (see snow totals in weather section below), we have 2 – 3 different mid-pack ice crusts, with various faceted layers in between, and depth hoar at the ground in thin areas.
Problem #1: Wind Slab
Location: Possible on all aspects, and especially cross-loaded terrain features/gullies, above 1,500ft. Last night’s new snow fell during a period of southerly winds, loading up North-ish aspects with fresh wind slab 15-45cm thick, sitting on weak surface facets and a hard bed surface. Today, north winds will be increasing in the alpine, which will reverse this wind loading pattern. Small natural avalanches will be possible in steep terrain, and human triggered slides will be likely on slopes 28 degrees and steeper, especially in wind loaded areas.
Test slopes, hand shears, and quick pits will be useful tools to evaluate this danger. Stick to areas where the top layer of snow is protected from the winds and not forming a cohesive slab. Always practice good travel techniques, utilizing safe zones and escape routes, only exposing one person at a time to slopes over 30 degrees.
Problem #2: Persistent Slab
Trend: danger slowly increasing. Location: all aspects above 1500ft. Likelihood of triggering: possible. Confidence: low. Below the upper rain crust, recent cold weather has been faceting (weakening) the layers in the midpack and at the ground in thin, windswept areas. We’re getting occasional reports of whumping within the facet layer below the upper ice crust, which shows that this upper ice crust is decomposing and getting weaker as a bridge. Be aware that you may be able to trigger pockets of deeper slab, and surface avalanches may step down to these facet layers. Use extra caution in thin areas, and carefully evaluate the presence of this potential danger on steep slopes, and especially on unsupported slopes.
Recent Avalanche Activity
In the last two weeks there has been small natural wind slab activity on wind loaded slopes, with crowns up to 25-50cm thick. This is occurring regularly in sync with wind events. Cross-loaded slopes have shown the most activity since the winds have shifted direction several times.
On Friday, north winds will help to clear out the clouds and move some snow around. Another storm is on tap for Saturday; it looks to be very similar to the storm we had Thursday night, with 2-6″ possible and winds southerly switching to northerly after the storm.
|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
|42″||2″ / 0.20||3″ / 0.30||0||mod, N||0″/ 0.00 *|
Flower Mountain @ treeline
|36″||5″ / 0.20||5″ / 0.50||0||mod, NW||0″/ 0.00 *|
Chilkat Pass @ 3,500ft
|23″*||4″ / 0.40 *||4″ / 0.40 *||0||mod, NW||0″/ 0.00 *|
( *star means meteorological estimate )
Additional Info & Media
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