A large human triggered avalanche occurred on 12/29 on the south face of Microdot.
See more detailed info HERE.
No other avalanches have been observed or reported this week.
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Yep, you guessed it! Persistent slabs , 1-3´deep, will be possible to human trigger today on all aspects, at mid and upper elevation, on slopes steeper than 30º.
It will be possible to trigger small avalanches in isolated or extreme terrain at low elevation.
Anywhere there is stiff snow, there is almost certainly weaker snow below it and this poor structure and potential for propagation is the avalanche problem. This slab-weak layer combo is widespread.
In places where the snowpack is thick, such as northerly and westerly terrain that has been wind loaded through the season, triggering persistent slabs will be possible, but less likely than the opposing southerly aspects. In places where the snowpack has remained thinner through the season, on southerly and easterly aspects, the snowpack consists of more developed facets and weaker snow grains. Wind events have cross loaded these aspects and deposited stiff snow (slab) in a patchy distribution on top of this very weak snow. To add more salt in the wound, a melt freeze crust is making for a slick bed surface. An example of this is the recent human triggered avalanche on Microdot on 12/29.
We continue to see persistent slabs propagate and fail in 3 different locations in the snowpack. The first layer is closer to the surface and consists of rounding facets. This layer is buried anywhere from 1-3’ from the surface. The second layer is near the ground and sits above a thin, supportable melt freeze crust. This layer consists of 1mm rounding facets and was buried on November 6th. This sugary snow was responsible for the near miss on 12/29. The third layer is a layer of depth hoar that sits at the ground.
While we continue this monotonous pattern of low probability, high consequence gambling with the persistent slab problem lets remember how to hedge our bets to stay safe. Hard slabs may break above you and make it challenging to impossible to get off the slab. We recommend finding low angle, 30° or less, wind protected terrain where the best snow lies, and is only marginally affected by the wind. These areas also generally lack the slab component, but are hard to find. Maintain appropriate distance and S-P-R-E-A-D out when travelling through avalanche terrain. Pay attention to other parties locations especially since remote triggering is possible. Stay out of harm’s way by skiing/riding one at a time, spotting partners, using appropriate safe zones, avoiding slopes with terrain traps, and using radio communication if possible. Lastly, pray that these conditions change with the New Year!
The video below shows our investigation of the hard slab conditions and attempts to explain our understanding of the spatial variability of the slab thickness as it relates to human triggering an avalanche.
Strong winds this season have been steadily building cornices along the upper elevation ridgelines on leeward aspects. Large, overhanging cornices are unreliable, difficult to predict failure, and pose a significant threat to people. Use extra caution around and near cornices, as they can break very far back from the actual ridgeline, often surprising travelers.
A large cornice failure will have the ability to injure or kill a person, with the potential additional hazard of triggering persistent slabs below.
New snow totals 12/27/20-1/2/21
Independence mine: less than 1″
Light winds at 4500′ since Thursday, with a max gust on Thursday of 15 mph and a max gust of 9mph overnight. Temps at 3500′ and 4500′ hovered in the upper teens to 20°F. The next chance for snow looks to be Sunday evening into Monday, with little precipitation expected.
A stale weather pattern with
Marmot weather station 1/1-2
Independence Mine 1/1-2
NWS Rec Forecast here.
NWS point forecast here.
State Parks Snow Report and Motorized Access information here.