Avalanche Forecast

High - The number, quality, or consistency of field observations is good, and supports our confidence.

THURSDAY NIGHT: Scattered flurries with 5-10 cm of new snow, moderate wind from the southwest, alpine temperatures around -5 C.

FRIDAY: Another 5-10 cm of snow in the morning then mix of sun and cloud in the afternoon, moderate to strong wind from the southwest, freezing level rises to 1500 m with alpine high temperatures around -3 C. 

SATURDAY: 5-15 cm of new snow then clearing in the afternoon, moderate wind from the southwest, freezing level drops to valley bottom with alpine high temperatures around -5 C.

SUNDAY: Mostly cloudy with some isolated flurries, light to moderate wind from the southwest, alpine high temperatures around -8 C.

A widespread natural avalanche cycle occurred Wednesday. Numerous large (size 2-2.5) natural and human-triggered avalanches were observed. Storm slabs appeared to be extra reactive above a recently buried layer of surface hoar and crusts down 40 cm (as seen in recent MIN reports here, here, and here). 

Last weekend, several persistent slab avalanches (size 1.5-3) were reported on deeper weak layers. These human and explosive triggered avalanches released on both the December surface hoar and November crust layers across a variety aspects. For example, this recent persistent slab avalanche was observed Sunday and scrubbed into the lower snowpack and was noted for being triggered on a shallow rocky convex slope. The possibility for large human-triggered persistent slab avalanches remains a serious concern, especially as sensitive storm slabs create the potential for avalanches to step-down to these layers.

Another 10-20 cm of new snow will add to the 30-50 cm of snow from the New Year's storm to create a widespread and touchy storm slab problem. The storm snow sits above a layer of surface hoar and a sun crust on steep sun-exposed aspects, which has contributed to the reactivity of the storm slabs. At higher elevations, ongoing wind transport will exacerbate the reactivity of storm slabs. There are multiple weak layers buried deeper in the snowpack, including two surface hoar layers (down 80 to 150 cm), melt-freeze crusts on steep south aspects (down 100 cm), and weak faceted snow near the bottom of of the snowpack. This fundamentally unstable snowpack structure remains a serious concern as the recent loading from new snow and wind has added significant stress to these weak layers.

• Make conservative terrain choices and avoid overhead hazard.
• Avoid freshly wind loaded terrain features.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.