Fresh storm slabs that formed Monday may be reactive to rider triggers especially on slopes that have seen more wind loading.
Confidence
Moderate - Wind effect is extremely variable on Wednesday
Weather Forecast
The arctic air mass dominates the region bringing the coldest temperatures of the season. Wednesday will be sunny with alpine temperatures near -18 and ridgetop winds light from the East. Thursday will be slightly unstable with a mix of sun and cloud and flurries. The next low will move into the Interior Friday with periods of snow and alpine temperatures near -12. Ridgetop winds will increase with strong gusts.
Avalanche Summary
On Tuesday, explosive control triggered numerous slab avaalnches up to size 2.5. These failed on NE-N aspects above 1750 m on, 50-100 cm deep, 50-100 m wide and running up to 500 m in length. These avalanches are failing on a previous graupel (ball bearings) interface and not digging deeper to the November crust layer. On Monday, numerous loose dry avalanches up to size 1 were reported after the storm as well as a natural size 2.5 storm slab from a northeast aspect above 1800 m. The crown was 20-100 cm thick, 150-200 m wide and running 500 m in length.
Snowpack Summary
New storm slabs and wind slabs have formed on open leeward slopes and behind terrain features while the mid pack is reportedly well settled. The threshold for avalanches has been exceeded at treeline and in the alpine as reports suggest that the snow depth at treeline is typically 110-150 cm but a report from the east side of region shows only 90 cm at treeline. The snowpack is just reaching threshold below treeline. Limited reports suggest the crust from the middle of November is down 50-80 cm and the crust from early November is down 80-110 cm.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.