Warm temperatures and sun could destabilize the upper snowpack and potentially cause slab avalanches, loose avalanches, or cornice failures. Watch your exposure to overhead hazards in the heat of the day.
Wind slabs could be problematic in wind exposed features in the alpine and near ridgetops. These slabs may become more sensitive to both natural and human triggering Friday as the warming temperatures and sun heat the upper snowpack.
A thick rain crust can be found 30 to 60 cm below the surface. As temperatures warm and slopes are subject to the sun, the overlying slab could start to wake up. Large cornices are a potential trigger for these slabs.
THURSDAY NIGHT: Cloudy, moderate southwest wind, freezing level drops to valley bottom overnight with alpine temperatures around -4 C.
FRIDAY: Mix of sun and cloud, freezing level climbing to 2000 m in the afternoon, moderate wind with strong gusts from the southwest. Increasing cloud and light snow starting in the evening.
SATURDAY: Cloudy with 5-10 cm of new snow, moderate wind from the southwest, freezing level drops from to 2000 to 1200 m.
SUNDAY: Mix of sun and cloud, light wind from the west, freezing level reaches 1200 m in the afternoon, alpine high temperatures around -2 C.
Wind slabs will likely remain reactive, as there was a report of a size 2 skier triggered slab on Thursday on northeast aspect near ridgetop in the Lizard Range. No new avalanches were reported on Wednesday.
A few size 1.5 skier triggered avalanches were reported on Tuesday that appeared to fail on persistent weak layers roughly 30-40 cm below the surface. One was triggered by a skier on a east-facing slope at 1900 m and ran on the early February crust/facet combo. This MIN observation from Harvey Pass shows a skier triggered avalanche on an north-facing slope that looks like it could have run on surface hoar. Sun and warming temperatures could weaken the snow above these persistent weak layers on Friday.
20 cm of settled snow rests on a variety of old surfaces including a firm crust on solar aspects, soft faceted snow, possibly a spotty surface hoar layer and old wind slabs near ridge crest. Recent snow has been blown into variable wind slabs in exposed terrain features, especially those near ridge crest.
A thick rain crust that has facets associated with it sits 30-60 cm below the surface and can be found up to ridgetop. The avalanche listed above is the first activity that we've seen on the crust since February 17.
The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.
