Avalanche Forecast

Fair - Timing, track, or intensity of incoming weather system is uncertain

The sub-tropical storm system continues to produce similar weather conditions on Thursday. Freezing levels will be around 2000m, alpine winds should remain strong, and we can expect another 5-15mm of precipitation. Things start to change on Friday as freezing levels should drop below 1500m and alpine winds ease during the day. Lingering precipitation is expected on Friday with amounts around 2-4mm. A ridge of high pressure is expected to begin to build on Saturday resulting in a mix of sun and cloud. Freezing levels are expected to be back down near valley bottom and winds should be calm or light.

Widespread natural avalanche activity up to size 2.5 was reported on Tuesday. These are primarily storm slabs in wind loaded areas and it looks like the bed surface may be the Dec 5 surface hoar layer and/or the late-November rain crust. Slab depths are typically 30-60 cm but one report has a slab depth up to 150cm, likely in a heavily wind loaded area. Natural activity is expected to continue as the next waves of the storm hit the area.

Rain to high elevations is saturating the upper snowpack.  A wet snow surface is expected up to 2000m elevation and moist snow to around 2400m. Strong winds are loading leeward features in the alpine. Below the new storm snow may be a layer of surface hoar which was buried on Dec 5. Below around 1800m elevation and down around 40-50cm is a rain crust. About 1m or so down, a weak layer of surface hoar and/or facets can be found in some locations. A thick rain crust with facets from early November is buried around 1.2 m down. Snowpack tests on these deep weak layers are showing slowly improving results, but in some locations these layers are still reactive and have the potential to release large slab avalanches. We may see these deep weak layers become a problem again as the storm continues to add new load.