Conditions 1/18
Sorry this is a couple days late. First time posting on the new website and trying to pick up the habit again.
We had a good L1 avalanche course over the MLK weekend. On Sunday around 9000' on a NE aspect in the June Mountain sidecountry, we found about 25-30cm of new snow on top of a thin, but strong, rain crust. The crust has facets above and below it. This facet/crust combo caused avalanches at the same elevation that we observed from JM avalanche control operations. There the layer was buried up to 4 feet by windload. We observed that the layer remained reactive on top of the crust with consistent CTH (21) results in Shovel Compression Tests with sudden planar fractures and we saw an Rutschblock RB 6, partial block failure.
On Monday during a strong storm pulse we went to 9200' in the backcountry near June Lake on a similar aspect. We found the same facet/crust combo with an overlying 40cm slab. With added load the weak layer seemed more reactive with consistent CTM, sudden planar failures. We also got an RB 4 with a sudden planar fracture. ECT results did not reveal potential for much fracture propagation at that time, but this is because the snow was very fresh.
By the end of the day on Monday there was 7-10 inches of new snow with little wind effects below 9000' in the trees we saw easily triggered sluffs and some minor cracking, but the new snow was too unconsolidated to propagate fractures. Now it is different, with additional load and time to settle the slab I suspect the storm snow will be primed for skier triggering on the facet/crust layer. This is concerning because the low elevation treed zones are probably exactly where most skiers will target during the storm.
Sue's advisory is right on. Big, unstable windslabs are the main concern as the storm progresses. While those concerns loom above, don't let your guard down in steep, low elevation, sheltered terrain either. The facet/crust layer may cause instability for a while longer than most people are accustomed to in our snowpack.
Enjoy and be careful! - H
