Avalanche Forecast

Saturday night: Clearing overnight, scattered flurries with up to 5 cm of snow, light southwest wind, alpine temperature -10 C.

Sunday: Mostly cloudy, convective flurries with up to 5 cm of snow, light southwest winds, alpine high temperature -5 C.

Monday: Mostly clear, light southwest wind, alpine high temperature -5 C, freezing level 1200 m. 

Tuesday: Increasing cloud, isolated flurries with trace accumulations, alpine high temperature -4 C, freezing level 1400 m.

Consistent reports of avalanches releasing on the February 22 surface hoar have been submitted over the past week. Human-triggered and remotely-triggered avalanches have been reported, even as professionals tiptoe around and avoid suspect terrain features. The problem is touchy but tricky. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group trigger the slab. These avalanches have propagated widely across terrain features, warranting conservative terrain margins (see this MIN for a helpful example). Avalanche size has increased over the past several days, with more of the activity releasing size 2+. Observations extend to all aspects and elevations, but north to east aspects near treeline have been a hot-spot for reactivity. Avalanches are also occurring at unusually high elevations for surface hoar.  

Several small to large (size 1-2) natural and human-triggered avalanches have been observed breaking in the recent storm snow. A few large (size 2) cornices were also observed failing naturally. If triggered, wind slabs and cornice falls could step down to the buried surface hoar layer, forming large avalanches. Use added caution on sun-exposed slopes when the sun is shining, as it could rapidly deteriorate the storm snow and cornices and cause loose or slab avalanches.

On Thursday, professionals reported large (size 2.5) explosive triggered avalanches releasing on weak layers near the ground. These avalanches occurred on north and east facing slopes above 2300 m, and they confirm that this problem remains a concern. 

Snowfall amounts varied across the region on Saturday, with the highest totals falling in the southern part of the region. Slab formation and human triggering will likely be specific to where the wind has transported the snow into deeper drifts.

A weak layer of surface hoar from February 22 may be found 35-70 cm deep. It may sit over a crust on solar aspects. With successive storms, more areas have reached critical loading and developed a slab over this layer. Riders will be capable of triggering this layer for some time until there is a substantial change in the snowpack. Read more about surface hoar on our forecaster blog.

Deep basal facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.

• It's critical to stay disciplined and choose only well supported, low consequence lines.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Stay off recently wind loaded slopes until they have had a chance to stabilize.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.