Impressive storm snow amounts of 60-100 cm have been received in recent days, resulting in a very large natural avalanche cycle on Tuesday. Give the snow time to settle and stick to conservative terrain with minimal overhead hazard.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
THURSDAY: Mostly cloudy. Ridge wind light to moderate, west. Alpine temperature near -8. Freezing level 700 m. Snow beginning overnight.FRIDAY: Flurries. Accumulation 10-15 cm. Ridge wind light to moderate northwest. Alpine temperature near -7. Freezing level 500 m.SATURDAY: Mix of sun and cloud. Ridge wind light, west. Alpine temperature near -8. Freezing level 800 m.
Avalanche Summary
A widespread natural avalanche cycle up to size 3.5 was reported on Tuesday following the storm. Storm slabs from 50 to 100 cm deep were reported on most aspects between 1400-2300 m. Southerly aspects were the most reactive with numerous large and very large (size 2.5 - 3.5) avalanches running on the most recently buried crust.
Snowpack Summary
Approximately 60 to 100 cm of recent storm snow has fallen with moderate to strong winds from the south / west. The storm snow sits on a variety of old snow surfaces: sun crusts at lower elevations and on south aspects, and older storm snow or wind slabs up high. Surface hoar layers have been reported on shaded aspects at higher elevations. Persistent weak layers from early January and mid-December are still being reported by local operators but are generally considered dormant. Large triggers such as a surface avalanche stepping down or a large cornice fall, or a human trigger in a shallow or variable-depth snowpack area could still be potential triggers. These layers consist of sun crust, surface hoar and/or facets.
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.