Quick report
- Red Flags
- Recent Avalanches, Heavy Snowfall, Cracking, Collapsing, Poor Snowpack Structure
- Red Flags Comment
- <p>Well advertised signs of instability aross the range. Due to limited visibility and travel challenges, we could not observe the recent slide on Pink PIne. No new avalanches were visible up the drainage in White Pine or across HWY 210. Every small low-angle slope we walked on visually and audibly collapsed with shooting tensile cracks.</p>
While travel was limited, we got bullseye info about the prevalence of the PWL buried on NW-N-E facing aspects at low elevation. Overall coverage is an inhibiting factor for traveling and the more desirable low elevation runs are difficult to ride. As more snow stacks up, these elevations will become more appealing, but the widespread distribution of weak snowpack structure will remain.
Photos from Pink Pine Ridge shoulder at 8700 NE'
1. While inserting the shovel on top of this compression test we had the column suddenly collapse and couldn't help but laugh at the weakness of the snowpack.
2. Short cut length resulting in a propagating crack to the end of the column on a PST at the same site.
3. In an area on the slope with a bit more wind drifting and more cohesive slab, we had full propagation on harder taps during an ECT.
4. Coverage.
5. Best view up drainage we had around 1pm. Profile locations and tests are from this worksite. Other sites lower on the ridge produced similar results.
Snowpack
- Instability Comment
- <p>We were uncertain about the distribution and sensitivity of the Facets originally buried by the December 9th storms, and being subsequently loaded by the storms on 12/14 and 12/16. Numerous collapses indicated the underlying structure to be weak. Even though the surface conditions remained pristine out of the wind affected areas. Digging multiple test profiles starting at 8400' on up to 8700'on North through East facing slopes revealed the true story. Facets (3-4mm) and Depth Hoar (5-6mm) was located as the primary culprit in these locations. At certain sites, an indistinct and decomposing melt freeze crust topped these weak grains. Slopes covered with vegetation such as alder and willow allowed for more pore space between grains for water vapor to move through and the grains were larger than we had observed at mid and upper elevation sites on similar aspects. We forecasted the distribution to be widespread and reactive, and we were not disappointed. Nearly every single ECT and PST showed propagation likely, failing with easy to medium taps or cut lengths less than 25% of the column. The only thing inhibiting wider propagation at this elevation was the dense vegetation and very soft overlying slab. However, the recent Pink Pine avalanche illustrates that it doesn't take more than a few hundred feet of open slope to allow for a slab avalanche to release. Parties we encountered in the area that were able to access this avalanche noted it was surprisingly well connected through the forest of conifers and aspen. </p>
At low elevation, The new snow depth from overnight was 10-15cm, but the storm that started 12/16 AM has produced upwards of 30-40cm of snow. This is on top of the 40-50cm that fell starting 12/14 PM. These two storms represent the majority of the HS at low elevations on northerly aspects at locations traveled.