The Bottom Line: Dangerous avalanche conditions exist due to heavy precipitation and strong south winds that have loaded persistent weak layers.  Some of these slides could be very large, step down to the ground, and run full path to hit lower runout zones in the valley bottoms. Avoid all avalanche terrain and runout zones today especially N-NW-W aspects. If you venture out, stick to forested areas and be careful to avoid any steep openings or gullies/terrain traps. Keep your slope angle below 30 degrees without any steeper slopes above or adjacent to you.

We have two buried surface hoar layers in wind protected areas, about 1-3ft deep. In addition, we have three lingering facet layers about 3-6ft deep, and at the ground (See Deep Slab problem below). Anywhere surface hoar is not present will likely have buried Near Surface Facets. There is still a lot of stress being stored in the snowpack and poor structure. Don’t be the trigger that unleashes this stored energy. Think about the connectedness of a hard slab, from where you are standing. If something is triggered on a steep slope or in a thin area nearby, does that slab connect to you, or above you? What about the rest of your group?

Never expose more than one person at a time to slopes 30-degrees and steeper, and don’t enter avalanche terrain without a plan for how to manage an avalanche that could break far wider and larger than you expect. Give yourself an extra margin of safety.

Surface Hoar Layers Beneath the New Snow:

• A new Surface Hoar layer from January 10th (pictured to the right) is now buried beneath this week’s new snow. We expect this new/old snow interface to be active during this storm cycle.
• The Dec 31 surface hoar layer is present in the Transitional and Pass zones, about 3ft deep. This layer has been active in pits, and caused some natural avalanches
• Buried SH layers are tricky — they’re hard to find, and may only exist in wind-protected areas. But anywhere they are present you should be highly suspicious of that slope.
• It would be best to avoid wind-protected pockets that may be harboring this dangerous weak layer. Make continual assessments on test slopes and with stability tests.

Photo of buried surface hoar 1/6 at Haines Pass near treeline at 2,500′ on S-aspect with ECTP 23 & 24 down 60cm that showed propagation potential. Above photo Surface Hoar at the Pass 1/10.

We should remain aware that very deep and wide destructive avalanches need to be considered and planned for accordingly. Pay attention to run-out paths and leave wide margins of safety for larger than expected slides. Terrain management is critical. An avalanche in the upper snowpack or cornice failures, within the new snow load could step down and lead to a massive avalanche.

Old Melt Layers and Crusts:

• A buried persistent weak layer about 6 feet deep (The “Big Warmup” Layer, Formed Nov 17th) is still a concern.
• It is a thick refrozen crust with weak faceted snow above. This is an unusual and unpredictable weak layer because it formed during a thaw event and then re-froze while cold temperatures faceted the stout crystals.
• A wide safety margin is necessary. This setup could produce avalanches that break wider than expected, and are most likely to be triggered from shallow trigger points like rocks or small trees. You could ride the same slope numerous times until that right spot produces a large destructive slide.

Photos of the “Big Warmup” facet layer in the Transitional Zone at 2500ft on 1/2 with test results ECTP18 that demonstrated propagation potential on this layer. And a photo from Old Faithful on 1/12 of a 5″ thick layer of facets down 170cm.

Observations in all zones throughout December and now into January have found moderate strength and quick propagation on failures within the “Big Warmup” crust/facet layer. We know it to exist at all elevations above 1000ft — even up to the highest summits. We expect this layer (and other midpack crust-facet layers) to be an ongoing issue going forward.

Depth Hoar at the Ground (Above 3,000′):

• October snow followed by long cold snaps created depth hoar at the ground in most areas. These angular snow grains are well developed into a weak layer that behaves like brittle glass.
• As the snow gets deeper, the load over this layer increases, and it could collapse. You are most likely to human-trigger this layer from shallow spots around rocks, or trees, or have a surface avalanche step down to the ground on this layer. Any slides that break to the ground are likely to be deadly.

Photos shows 6-9mm advanced depth hoar at the ground down 180cm with ECTP 25 down 80cm on facets below a crust in the Haines Pass Zone at 4,000ft on a NE-aspect.