Quick report
- Red Flags
- Recent Avalanches, Heavy Snowfall, Wind Loading, Poor Snowpack Structure
- Red Flags Comment
- <p>Wind loading on suspect facet/crust structure on southerly aspects are of concern. </p>
Photos:
1-skin tracks refilling at the mid-elevation northerlies
2-Looked like a size 2 natural on SE facing Cardiff below the cliff bands, likely at the facet/crust interface?
3-The return to LCC. We chose to stay high and regain the Eyebrow/Cardiff Peak ridgeline for our return to Cardiff Pass. Why? The upper north facing Cardiff bowl ran wall-to-wall into the old faceted snow with the Thankgiving storms and would naturally be thinner and rockier. Also...graupel slabs tend to pool beneath cliffbands - where the long traverse often goes.
4-The Thursday 420am large natural (size 4?) in Tanners.
Ski tracks noted in High Ivory, Cardiac Ridge and the Hallway today without incident.
Noted no step downs into old snow in our travels today.
For Saturday, I would continue to avoid recently wind drifted terrain (winds f/c to continue overnight/tomorrow).
Snowpack
- Instability Comment
- <p>Moderate to strong sustained northwest winds. Even mid-elevation north-facing skin tracks filled back in through early afternoon. Wind drifts should still be avoided on Saturday, particularly in areas with a south/southeast component up high and variable at the mid-elevations. An interesting and critical snow structure difference on northerly and southerly (southeast to west) aspects. This has been hit upon by Gagne and Englehard.</p> <p> </p> <ul> <li><strong>Northerly aspects</strong> have weak interfaces at the storm snow with slightly faceted low density stellar dendrites. <strong><em>It was quite active on Thursday during the heaviest loading events.</em></strong> Today we found mixed results and propagation at this interface. This interface should settle down soon.* Photo below.</li> <li><strong>Southerly aspects </strong>suffered sun damage and formed a thin crust prior to the storm, with faceting of the stellars occurring just below this crust. This facet/crust combination (why I clicked 'poor snow structure) - as evidenced in multiple snowpits today (video below) - likely played the significant role in the larger avalanches (impressive connectivity and propagation of size 2,3, perhaps 4 - in Tanners Gulch) on Thursday. This structure may settle out more slowly. </li> </ul> <p>Catherine Brown, a grad student at ASARC with Dr. Bruce Jamieson in the early/mid 2000s looked at the mechanical properties of new (non-persistent) weak layers. I spoke with her after her presentation in Telluride ISSW 2006. Stellars are interesting in that they can behave initially, with enough loading, as surface hoar (remote triggering)...and tend to hang on and be active longer than many of the other new snow types. They also facet readily. </p> <p><a href="https://arc.lib.montana.edu//snow-science/item.php?id=158">https://arc.lib.montana.edu//snow-science/item.php?id=158</a></p> <p><a href="https://arc.lib.montana.edu//snow-science/item.php?id=897">https://arc.lib.montana.edu//snow-science/item.php?id=897</a></p> <p>Ned Bair and others have looked at this recently as well. </p>
Some damage with today's sun and wind, but rode well in the high density snow and graupel.