PWL and Wind Slabs on Castle Peak

10 to 16 inches of new snow existed in the Castle Peak area today. Wind slabs formed by wind transporting this new snow existed on wind loaded N-NE-E aspects as well as some SE and NW aspects at all elevations. Some of these wind slabs were hard slabs and others were soft slabs. They all rested on top of loose snow from earlier this week and ski cuts and ski kicks triggered cracking up to 18 inches deep on NE-E facing test slopes at 7400 ft (39.345741, -120.348830), 7800 ft (39.355033, -120.340890), and at 8400 ft. At the test slopes at 7400 ft. and 7800 ft. the approach of a skier triggered a collapse at the interface between the new wind slabs and the snow that fell last week and resulted in whumfing noises. Natural wind slab avalanches also had occurred on the ENE facing ridge between Basin Peak and Castle Peak and possibly on the E-NE facing slopes near the summit of Andesite Ridge (limited information about these slides here). Wind scouring also existed on some of the upper elevation slopes on southerly and some northerly aspects due to winds shifting during and after the storm.

Photo 1: NE facing test slope at 8400 ft. where a ski kick triggered a cracking and a small release of an 18 in deep wind slab.

Snowpit data from a low angle representative slope on north side of Castle near the ridge revealed weak layers below last night's snow at the upper elevations. While some inconsistency existed in the snowpit tests results, Many tests indicated that fractures could travel along a weak layer at the base of last night's snow and along the 11/16 facet layer below last week's snow. Some tests indicated that this lower layer has become more difficult to trigger.