There is about 4-6" of new snow in this zone, and winds have been moderate and variable over the last 48 hours, blowing from the NW and the SE at times. Rain line reached up to about 3500ft Friday, before falling to the valley floors during a period of heavy snow Saturday morning.
Problem #1: Wind Slab:
Location: Specific slopes in the alpine above 2,000ft, where north/NW winds the last three weeks caused wind loading on lee aspects beneath ridgelines and terrain features. Reports this week found areas of wind slab (3-12" thick) that are poorly bonded and easy to trigger. These new wind slabs are sliding on a buried surface hoar layer and/ or buried facets 10-30cm deep. Be sure to dig around in high-alpine areas to assess for yourself how well-bonded the upper snowpack is. Variability will be high, so evaluate each slope carefully. Hand pits and slopes tests will be helpful in mapping out this potential danger. In large or steep terrain, slabs as thin as a few inches can sweep you into dangerous situations.
Problem #2: Deep Slab:
Location: Chilkat Pass Zone, all aspects above 3,500ft. Avalanche Size: Large. Likelihood of Triggering: Possible.
We've had mixed reports of lingering weakness in an old facet layer about 80-100cm deep (more like 45cm deep in shallower areas near Nadahini). These 2mm facets are sitting over a slick rain crust, and have produced isolated deep avalanches during storms over the last few weeks. In some areas (mainly lower elevations with deeper snowpack) this layer is not reactive, but we did get one report of easy triggering on this deep weak layer in snowpit tests from the north slopes of Mineral Mountain on January 3rd, and another from Nadahini area on Jan 20th. The most likely way to trigger this layer will be from areas of thin snowpack, near rocks and ridgelines. Heavy triggers such as snowmachines, cornices, or hard cliff drops increase the odds of collapsing this weak layer. Remote triggering will be possible, so careful group management and wide spacing is essential. The best way to manage this danger is to plan for the unpredictable, and know where your safe zones are. Consider the consequences of a slab this deep ripping out before you commit to avalanche terrain.
Above: Nadahini snow pit from 20-Jan-2019
Above: Deep slab avalanche in the Chilkat Pass zone from early January. NE aspect near 5000ft.
Observations this week found areas of D1-D2 thin natural windslab avalanches on specific terrain that was wind loaded or cross-loaded, between 2500-5000ft. These wind slabs were sliding on low-angle slopes as low as 25 degrees, and appeared to be sliding on a buried surface hoar layer 10-30cm deep. Distribution of these avalanches was limited to wind loaded areas that had been protected from strong N/NW winds.
Saturday's storm should start clearing up in the afternoon, bringing in a beautiful day Sunday with clearing skies and light winds, and temperatures just below freezing. The next storm is on tap for Monday night-Tuesday, and it should be another warm/wet one with snow levels up to about 3000ft.
( *star means meteorological estimate )
If you get out riding, please send in an observation!
Do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and KNOW HOW TO USE THEM.
Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.
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