The snowpack is complex with numerous concerning avalanche problems. This uncertainty warrants conservative terrain choices.
Strong to extreme wind from the west has left unstable wind slabs at upper elevations. Wind slab avalanches in motion could step down to buried weak layers and release very large persistent or deep persistent slab avalanches.
30 to 50 cm of settled snow rests on a widespread layer of buried surface hoar. While this weak layer is thought to be present at all elevations, these slabs have been most sensitive to triggering at treeline which is a setup that can catch us off guard. Watch for deeper slabs at ridgecrest too.
Recent loading from new snow and wind has aggravated the deep persistent slab problem. Some very large and destructive avalanches have been sporadically failing on deeply buried weak layers, predominantly on north through east aspects in the alpine. Cornice falls are a likely trigger for these slabs.
TUESDAY NIGHT: As the storm tracks south another 5-15 cm of snow accumulates, strong northwest wind, alpine temperature drops to -12 C.
WEDNESDAY: Cloudy with some isolated flurries and up to 5 cm of snow, moderate west wind, alpine high temperatures around -8 C.
THURSDAY: Scattered flurries with 3-8 cm of new snow, strong south wind, alpine high temperatures around -6 C.
FRIDAY: Mix of sun and cloud, light southwest wind, alpine high temperatures around -8 C.
Poor visibility since the arrival of stormy weather on Sunday has limited observations, however natural wind slab avalanches are likely occurring in alpine terrain. Over the past few days there have been reports of wind slab, persistent slab (failing on the February 19 surface hoar layer), and deep persistent slab (failing on basal facets) avalanches. This pattern highlights how the current stormy weather is aggravating multiple weak layers in the snowpack.
Almost every day since last Thursday there have been size 1 human triggered persistent slab avalanches on the Feb 19 surface hoar layer. These have typically been 30 cm thick and occurred on a range of aspects. There have also been several reports of natural size 2 wind slab avalanches on all aspects in alpine terrain (including these great photos from a MIN report at Ashman). Many have been triggered by cornice failures on north and east facing slopes. Last Friday, a natural cornice failure produced a size 3.5 deep persistent slab on a northeast facing feature at 1800.
Extreme wind from the southwest, west, and northwest has hammered open terrain, scouring some slopes and forming wind slabs on other slopes.
Loading from new snow and wind has made several persistent weak layers problematic over the past week. A combination of surface hoar and sun crust layers were buried on February 19 and currently sit 30-50 cm below the surface. The surface hoar may be most sensitive to human triggering at treeline which is a bit different setup than we're used to. A couple of weak layers that formed in January are buried in close proximity to one another 80-140 cm below the surface. Below that, an early season crust/facet layer lurks at the base of the snowpack.
