Observation: Public

Observation Details

Observed Avalanches

Signs of Unstable Snow

Observations

We traveled between 5200' and 6700' south of White Pass ski area, skiing low-angle bowls and seeking moderate terrain to navigate the persistent weak layer du jour (facets over the March crust 50-60cm down on N-NE-E terrain), which presented all of the apparent red flags: cracking, collapsing, and recent avalanches.

The day started cool with sun breaks and cold surface snow at all aspects, but was overcome by westerly flow, rising humidity, and warming solar slopes by mid-afternoon (1530). We dropped into our tour adjacent to an intentional, cornice-triggered (or remotely-triggered) small hard slab near 6700' on east (Avalanche 1 - HS-AC-R1-D1.5). We experienced cracking within sensitive wind slabs and cornices as we skinned on the same ridgeline. During our first run, we dropped around a corner and saw a recently reported skier-triggered avalanche near 6000'/E-NE (Avalanche 2 - SS-ASu-R2-D2 - crown broke widely, propagating 200' across and running 400').

At 5700' on a NE slope, we found a weakness in the terrain where we investigated snowpack structure before gaining the bowl we intended to ski. Just prior to digging we got an audible collapse in flat trees at 5600'. We would also later collapse this slope where our skin track travelled on the third lap (15' radius) around 5800'. Our pit NE at 5700' showed that recent storms and wind had built a slab of 50-60cm over the March crust and facets. When tested this layer, as foreshadowed by the surrounding recent avalanches, had clear propagation potential: CT11 and CT13 with sudden planar shears @55 and 60cm, and PST 20 end, with the 55cm deep block cash registering out.

Minding the heads up conditions, we made pleasant low-angle NTL wiggles, noting another large D2 avalanche from Thursday or early Friday (Avalanche 3 - HS-U-R2-D2-O; 6400' E); it potentially started as a tree bomb or wet loose that broke to slab, but may have also been triggered remotely from the ridge above.

Unsurprisingly, the PWL was not reactive under foot travelling in wind and sun-affected NTL areas where the slab is harder and more connected than the soft slabs BTL. We didn't trust this false positive, and stayed off of steep, northerly terrain that we had closed prior to our tour.

Take away: the PWL in the west south isn't playing around, and although it's deep enough that it doesn't present itself under foot, it's real and causing frequent avalanches that are large enough to bury a skier.