Avalanche Forecast

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Saturday

Friday offers another day of rather benign weather before the storm track takes over Friday night into Saturday. The clouds begin to fade away Sunday giving way to what looks to be a pretty robust ridge of high pressure that we will ride into the New Year.THURSDAY NIGHT: Freezing level at valley bottom, light southwest wind with moderate northwest gusts near ridgetop, trace of snow possible. FRIDAY: Scattered cloud cover at dawn building to overcast by sundown, freezing level at valley bottom, light southerly wind at valley bottom with moderate west/northwest wind in the alpine, 1 to 5 cm of snow possible during the day with 10 to 25 cm expected Friday night.SATURDAY: Storm day, Overcast, freezing level beginning at valley bottom, rising to around 1500 m by sunset. Strong to extreme southwest wind, 10 to 20 cm of snow.SUNDAY: Broken cloud cover, freezing level at valley bottom, moderate north/northwest wind, trace of snow possible

No new avalanche activity to report from Tuesday or Wednesday. On Monday a natural size 3 glide avalanche was reported from a steep south facing aspect at 1500 m. The avalanche likely failed on the ground running on what looked to be a grass slope from far away.A few large (size 2-3) natural persistent slab avalanches were reported on Sunday. These avalanches were reported on south aspects in the alpine. Last week numerous persistent slab avalanches (up to size 3) were reported on all aspects (a few that even destroyed mature trees). The persistent slabs were 50-150 cm thick and likely failed on the early December weak layer. The same layer was responsible for several large human triggered avalanches earlier this month (see this MIN report for an example).

Low density snow from the past few days sits above wind affected snow in the alpine and around treeline.A weak layer that formed during the dry spell in early December is now 90-160 cm deep. The layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. VARDA has posted a video that provides a great visual on our snowpack. This layer was previously responsible for large persistent slab avalanches, but activity has greatly diminished over the last week. Saturday's storm may breathe some life into it, the places of greatest concern will be north and east facing slopes between 1900-2300 m and steep south-facing slopes in the alpine.A weak layer from mid-November and a crust that formed in late October are found near the bottom of the snowpack. The probability of triggering these deeper layers is low, but the most suspect areas would be shallow spots in steep rocky terrain.