The Bottom Line: Human triggered avalanches on recently wind loaded SW-NE aspects are likely today. Smaller slides could trigger lower persistent layers and step down into very large, deep slides that could run full path to hit lower runout zones in the valley bottoms. 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.

Above 2,500′ significant snowfall of 1-2′ or greater combined with strong south winds have loaded SW-NE aspects. Avoid these aspects that are primed with fresh wind slab and where human triggered avalanches are very likely. Also, keep in mind the new/old snow interface about 2′ deep consists of crust/facet combo layers and were noticeably weak recently.

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 to avoid these slopes. 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.