Avalanche danger will be high to borderline extreme Friday. With three-day snow totals expected to reach 24″ at the Pass and 36″ near town, extreme danger is possible Saturday-Sunday.
Above 2,500ft High
1,500 to 2,500ft High
Below 1,500ft Considerable
Degrees of Avalanche Danger ?
6-12″ of new snow has now obscured the wind slabs built up from last week, making it quite difficult to avoid these dangerous areas of persistent slab.
Bottom line: A layer of weak facets buried underneath last week’s new snow (about 40-75cm deep) is still active and touchy. Widespread danger signs exist, including whumphing and skier-triggered slides over the last few days. Wind loaded slopes steeper than 30 degrees are still quite dangerous, even in the trees (see photos below).
Problem #1: Persistent Slab
Location: All aspects and cross-loaded gullies, above 1500ft. With the strong southwest winds last week, followed by northerly outflow winds, we have areas of thick recent slab deposits under the new snow on all aspects. These slabs are hard and hollow above treeline, and softer in the trees, with weak 3-4mm buried surface facets underneath. Due to the nature of the weak layers and the continued cold weather, bonding is poor, and collapsing is common. Remote triggering has been a common report. These slabs could be anywhere from 15-75cm thick, and will be sensitive to human triggering on slopes steeper than 30 degrees.
Resist the temptation to try out big terrain. We have not had a stabilizing event to reduce these surface instabilities, and we have not had enough time or warm weather to bond the weak layers.
We now have a “loaded gun” type of scenario where wind loaded slopes are stressed and waiting for a trigger.
Remote triggering and wide propagation will be possible, leading to large avalanches. Surface avalanches may step down to deeper facet layers 45-80+cm deep, below the upper ice crust.
Problem #2: Storm Snow
Location: All aspects and elevations, slopes 30 degrees and steeper. New snow totals from Wednesday are around 6″ in the Transitional zone, and 12″ in the Lutak zone. Mountain winds were light-moderate out of the South, so expect some wind affect and loading on northerly aspects and cross-loaded terrain features. On any slopes steeper than 30 degrees where the new snow is wind-affected and cohesive, you will be able to trigger soft slabs, as bonding is poor right now.
Recent Avalanche Activity
In the last week, lots of whumphing, shooting cracks, and slide activity has been reported (failing on facets above and below the upper ice crust).
Several slides have been occurring in the trees around 2500-3500ft, on any aspect where the recent snow has loaded up. Photo below is the result from a ski cut. [ SS-ARc-D2-R2-O, E aspect at 3500ft, 40 degree slope, crown 30-45cm deep ] ran on 3mm facets above the ice crust. Lutak Zone, 3/4/2018.
There has been sporadic natural wind slab activity to size 3 in the Lutak and Transitional zones, mostly on wind loaded south aspects over the last week (see photo 1 below). In a few heavily-cross loaded areas around 4000ft, natural slides broke below the ice crust on persistent facets (photo 2 below).
Thursday will bring a break between storms, with some clearing of the clouds. A strong storm will hit around midnight Thursday night with heavy snow and gusty south winds over ridge tops. 6-12″ of new accumulation is likely by Friday evening (lower amounts at the Pass). Continued snowfall is likely through Sunday.
|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
|55″||12″ / 0.80||12″ / 0.80||0||light, S||9″/ 0.80 *|
Flower Mountain @ treeline
|40″||6″ / 0.40||6″ / 0.40||0||light, S||6″/ 0.50 *|
Chilkat Pass @ 3,500ft
|20″*||3″ / 0.20 *||3″ / 0.20 *||0||light, SE||4″/ 0.30 *|
( *star means meteorological estimate )
Additional Info & Media
If you get out on the snow, send in your observations!