The Bottom Line: We are finally getting heavy precipitation and warmth, which will likely cause a natural avalanche cycle today. 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. If you venture out, stick to forested areas and be careful to avoid any steep openings or gullies/terrain traps.

Below 2000ft on all aspects, we have had plenty of rain to saturate the upper snowpack layers and cause natural wet slabs and large point releases. Wet slides continue to be likely today in these middle-elevation areas. Stay away from terrain traps and slopes 30-degrees and steeper.

Any avalanches coming down from the Alpine may entrain large amounts of wet snow and continue full-path down to lower runout zones.

Above 2000ft: The Lutak zone has received 15″ of new snow already, with up to 18″ more coming today through Saturday. Needless to say, this is plenty to move around in steep terrain. Wind affected areas will be slabby and tender with natural and human-triggered avalanches likely. The new/old snow interface about 2ft deep consists of crust/facet combo layers that 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.

Smaller avalanches in the upper snowpack or cornice failures could step down, leading 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.