March 25, 2023 - March 25, 2023
March 25, 2023
Clancy Nelson | ESAC Forecaster
Zone or Region:
Bishop Area - Tricky Persistent Slabs
We went looking for the persistent slab problem at the southern end of the forecast area and found it a little tricky to predict.
- We triggered long shooting cracks on a northwest aspect at 8300 feet. We got easy propagating test results (ECTP1) on a north-northeast aspect at 9000 feet. We got a big collapse and shooting cracks at 9900 feet on an east-northeast aspect. All of these failed on a mixture of decomposing/fragmented grains and near-surface facets (0.5-2.0 mm) buried on March 19th. At the first two locations, the weak layer was under thin (10-15cm) hard (1F-P) wind deposits and above a melt-freeze crust. When we got our collapse at 9900 feet, the weak layer was under a foot of snow and sat atop a dense (1F) wind-packed layer.
- We found 2 natural avalanches that failed under, or because of failing cornices on northeast aspects near 10,000 feet. One of these was right next to our big collapse and we confirmed that it had failed on the 3/19 layer. I suspect these slid on 3/23 or 2/24 when the winds were elevated at the North Lake wind station and we also had several reports of natural wind slab avalanches in June and Mammoth.
- It was a calm day with no blowing snow and we saw no other signs of instability.
- Skiing was variable across sastrugi and grabby crusts on windward and solar slopes, punchy-to-soft-to-dense wind drifts on leeward slopes. There were a few stripes of soft snow here and there.