The last storm cycle ended January 1st. It featured strong SE winds, and 1-2.5" of SWE. It rained up to about 4000ft for a few hours at the end of the storm. Temperatures have since cooled down rapidly and we're now getting into a deep freeze with arctic outflow. This pattern will bring moderate north winds and clear weather for the next several days.
Problem #1: Wind Slab:
Bottom line: our snowpack was rocked pretty hard by heavy snow then rain-on-snow earlier this week. Now that it is freezing solidly, bonding of recent storm layers is expected to increase. The main exception will be specific slopes in the alpine above 4,000ft, where increasing north winds may be enough to cause fresh wind loading on lee aspects beneath ridgelines and terrain features. Any new wind slabs that build up will be cold, weak, and prone to human triggering. If you see areas of recent/active wind loading, be sure to avoid these areas.
Further, if you venture onto slopes above 4500ft, remember that these colder areas may have lingering wind slabs from the last storm that could be a concern in steep or large terrain. Human triggering of slabs 30-90cm thick from the last storm will be more likely as you increase in elevation. Be sure to dig around in these high-alpine areas to assess for yourself how well-bonded the recent snow is.
Practice good risk management out there this weekend, 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.
Problem #2: Deep Slab:
Location: Chilkat Pass Zone, all aspects above 3,500ft. Sensitivity: Stubborn. Avalanche Size: Large. Likelihood of Triggering: Possible to Unlikely.
We're still getting mixed reports of lingering weakness in an old facet layer about 80-100cm deep. 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. 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.
Photo: A D3 natural deep slab avalanche from 2 weeks ago, NE aspect, Chilkat Pass zone. Ran on the facet/crust layer mentioned above.
Cold and dry offshore flow will persist for the next several days. North winds will be moderate in the alpine, probably enough to cause some wind loading around high ridgelines and alpine couloirs / gullies.
( *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. Come to our FREE backcountry skills workshop on January 10th (see flyer below).
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.
Be sure to read through the Deep Slab concerns detailed in the full forecast for the Chilkat Pass zone. Extra caution should be used in alpine areas of the Pass this weekend.
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