Deep unconsolidated new snow, with light to moderates winds have likely built wind slabs on specific terrain features above tree line. Human triggered avalanches are possible. Look for strong over weak layering at the surface, a punchy feel that tells you you’re on a slab, or textured wind deposits. While the danger is mostly moderate for this problem, pockets of considerable do exist especially over any deep persistent weak layers. An increase in wind speed/direction could indicate elevated hazard and make human triggering more likely. Be vigilant to any changing conditions, avoid run out zones and stay aware when others are above or below you. Wind slabs range from predictable to unpredictable due to slab stiffness and spatial variability.
Persistent weak layer concerns since early December are now buried under the weight of the new snow, and are deep enough that the likelihood of triggering one of these deep slab avalanches is unlikely. Remember that shallow, or thin areas in the snowpack could be ripe for access to these deep instabilities. Travel where the snowpack is fat and make assessments where it is not. This will help save some time digging. Think about how upper layers over the terrain could communicate to layers further down in the snowpack. Minimize exposure, use terrain wisely, avoid excess time in run-out zones, practice safe travel technique and remember how your decisions effect yourself and others.
Bottom Line: Heavy snowfall over the last week with freezing levels up to 1,500′ have helped the snowpack “crush” deeper buried weak layers, without the “flush” or large scale natural avalanche cycle. Surface instabilities are the greatest concern, mostly above treeline where pockets of considerable wind slab danger could still exist. Keep in your decision making framework, the drawn out global pandemic response and taxed EMS resources.
Good News: The snowpack is getting deep! So, it is a great time to identify where the snowpack is not deep. Areas of shallow, underlying terrain could be rocks, cliffs, trees, vegetation, or un-supported slopes where it would be easiest to trigger deeper buried weak layers. These would be good areas to avoid riding, or further inspect to make risk assessments. Don’t be shy pulling out your probe to feel for strong over weak layering beneath you.
In the last week, 61″ of new snow fell in the Lutak zone, 30″ in the Transitional zone, and about 18″ at the Pass. Freezing levels briefly rose to 2,000ft on the 19th and 23rd, but otherwise stayed near 500ft. Looking forward, a storm will glance us on the evening of the 25th, with 1-3″ of snowfall expected by Saturday. After that, the weather looks mostly clear and cold through New Years.
( *star means meteorological estimate )
When is the last time you and your riding partners practiced companion rescue? Dust off your gear and make sure it is fully functional. Put new batteries in your beacons! Make sure everyone in the group has a functioning beacon, shovel and probe – and knows how to use them, keep your skills fresh. If you head into the hills, watch out for avalanche conditions, and be especially careful of rocks and hidden hazards like crevasses beneath the snow. WEAR A HELMET!
Education Video Links:
We have begun conditions updates for winter 2020/2021. Click the + Full Forecast link below for each zone to read more. Submit observations. Win prizes. Each snow, weather & avalanche observation outside of the HAC staff will be entered in a raffle drawing. The more observations, the more chances to win!
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