Two human triggered avalanches occurred on 12/3 on SW aspects on Marmot. One was human triggered from the ridge at approx. 4000′ and failed on persistent grains and was large enough to bury, injure of kill a person. The other was a D1.5 and was remotely triggered at approx. 3200′ from 30′ away and also failed on persistent grains.
A D2 slab avalanche was observed in Rae Wallace and believed to have occurred during the wind event 12/2-12/3. If you have information about this avalanche, please contact us. Most of the avalanches in this photo (below) are old. The one to the left is new.
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Persistent slabs will continue to be a problem this weekend on all aspects, at the mid to upper elevations. They will be possible to human trigger, small to large in size, up to 3 feet deep, on slopes 35 ° and steeper. Remotely triggered avalanches will be possible from the flats below a steeper slope, from adjacent terrain, or from a distance. Hard slabs will allow you to get out onto a slope before failing above you, making escape very difficult to impossible, and ski cuts ineffective.
Persistent slabs will be unlikely to human trigger at low elevation, but may be possible in very isolated locations. Most of the snowpack at low elevation is comprised of sugary, faceted snow and lacking a slab component.
This problem is very difficult to predict and carries a high level of uncertainty. Due to a generally shallow snowpack, being caught and carried in any avalanche also carries the added risk of rock hazards.
There are two different persistent slabs that currently exist in the snowpack.
One problem is shallow in the snowpack, up to a 1 foot deep sitting on an old layer of near surface facets. This slab formed from the early December wind event, and is generally located on West to North aspects.
The deeper problem, up to 3 feet deep, is a persistent slab sitting on an old, weak layer of facets near the ground which were formed in October. This problem can be found on all aspects and elevations.
Considering the lingering, unreliable and uncertain nature of this problem, we recommend conservative terrain choices, lacking any terrain traps. Recent avalanches, whumphing, collapsing and shooting cracks are all red flags for this problem. If you encounter stiff snow, expect that it us sitting on weaker layers below and therefore suspect. We recommend testing the snow with pole tests, hand shears, and instability tests. Spot your partners, ski/ride one at a time, and use appropriate safe zones out of the way of any potential avalanche.
NWS Rec Forecast here.
NWS point forecast here.
State Parks Snow Report and Motorized Access information here.
Hatcher Pass received 3-4″of new snow on 12/1. Moderate winds earlier in the week tapered off Wednesday afternoon.
Marmot Weather Station 4500′
Marmot Winds- 12/3-12/5
Independence Mine 3550′
Temperature last 7 days