Carefully assess your line for wind slabs before committing. Steep, convex slopes below ridges are the most likely places to trigger these slabs.
Recent southwest winds and fresh snow formed wind slabs in lee terrain features. Now in a west-northwesterly flow, winds may "reverse load" slopes, building fresh wind slabs on more south and easterly aspects. Carefully assess your line for wind slabs before committing. Steep, convex slopes below ridges are the most likely places to trigger these slabs.
New cornice development with touchy characteristics were observed on Sunday. Where cornices exist they pose a threat both from the potential for them to collapse under your feet (or machine) and from the potential to send large chunks of snow far down a slope. They are most likely to fail during periods of solar radiation or loading from snow/wind.
MONDAY NIGHT: Patchy clouds. Moderate northwest wind, alpine low -12C, and freezing level valley bottom.
TUESDAY: Patchy clouds, sunny breaks, and isolated flurries. Light to moderate west wind, alpine high -1C, and rising to 1500 m.
WEDNESDAY: Snow, 5-15 cm. Moderate southwest wind, alpine high 0C, and rising above 1500 m.
THURSDAY: Flurries, 5 cm. Light west wind, alpine high -1C, and freezing level beginning about 1600 m.
On Monday, explosives triggered several size 1-1.5 avalanches on NW-N-NE aspects above 1800 m. At upper elevations, skies triggered small dry-loose avalanches in steep terrain. Below tree line, loose-wet and wet-slab avalanches gained reactivity to skiers in the afternoon. And several natural storm slab avalanches size 2-2.5 were reported in Glacier NP, occurring on north-northwesterly aspects above 1950m.
On Sunday, explosives and skier traffic triggered numerous size 1 avalanches, new and touchy cornices were observed. A few small dry loose avalanches and sluffing in steep terrain was also reported.
On Saturday, explosives triggered small (size 1-1.5) storm slabs from north-northeast aspects above 2000 m. A skier also triggered a small (size 1) wind slab on a steep convex roll on an easterly aspect at treeline. Sluffing was reported in steep terrain. In Glacier NP, a handful of storm slabs size 1.5-2.5 released naturally from steep north-northwest aspects above 2000m.
On Friday, several glide slab avalanches (size 2-3) were observed on south and east aspects around the TCH highway corridor. Loose wet avalanches up to size 2.5 were reported around the region; a natural loose-wet cycle was reported around Rogers Pass initiating with evening rainfall.
Southwesterly winds have developed slabs in lee features. 20-35 cm storm snow (up to 60 cm in areas) covers a handful of surfaces: dry settled snow and surface hoar (up to 10 mm) on northerly aspects above 1800m, and crusts on solar aspects and lower elevations. Sun and warm temperatures have encouraged settlement. Large cornices loom over alpine ridgetops. Below 1500 m, the snowpack turns moist.
Persistent weak layers of surface hoar, crusts, and/or facets 80-120 cm down have recently been unreactive and no recent avalanches have been reported on these layers.
