Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Saturday night: Partly cloudy, scattered flurries with up to 5 cm of snow, light northwest wind, alpine temperature dropping to -16 C.

Sunday: Mix of sun and cloud, light northwest wind, alpine high temperature -17 C.

Monday: Mainly sunny, light west wind, alpine high temperature -22 C.

Tuesday: Mainly sunny, light northwest wind, alpine high temperature -25 C.

Three different flavors of avalanches can be expected on Sunday. Loose dry avalanches may be possible in areas where the recent snow has not formed a slab. Although typically small (size 1-1.5), these avalanches pose a serious concern for ice climbers and for people traveling in extreme terrain where the possibility of getting knocked off of your feet has severe consequences. At upper elevations, newly formed wind slabs are expected to be reactive to human triggering. At treeline elevations and below, avalanches may be remotely triggered and break larger than expected on a reactive layer of surface hoar. 

Since Friday, there have been numerous reports of natural and skier-triggered avalanches breaking 10-30 cm deep in the recent storm snow. Several small dry loose avalanches have also been observed.

On Thursday, a large (size 2) skier-triggered persistent slab avalanche was reported near the Gorge area. This avalanche failed on the surface hoar buried 60 cm deep. There have been many recently reported avalanches on this widespread surface hoar layer throughout this region. Here is one excellent example from the Gorge area and another from Corbin Pass.

Another 10-15cm overnight with strong winds from the northwest have formed fresh wind slabs in lee features at upper elevations. With up to 25 cm of low density snow from the past couple days, cohesion-less snow in sheltered areas may be prone to dry loose avalanches.

The snow from the past week is settling over a reactive weak layer of surface hoar buried 60-100 cm deep. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. Recent avalanches on this layer have primarily been reported at treeline and below. This layer will be slow to gain strength and requires careful terrain selection.

A less reactive layer of surface hoar or facets buried in early January can be found down 80-130 cm.

The mid/lower snowpack is generally well settled and strong. 

• Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
• Stay off recently wind loaded slopes until they have had a chance to stabilize.
• Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.