Bollettino valanghe

Bollettino valanghe

Payette Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Happy 2021!  Based on the upcoming weather forecast, it looks like 21 is going to be pretty darn good if you like fresh snow! 

The Avalanche Danger is Moderate today above 7000 ft.  Unfortunately, the persistent slab problem  that we have been talking about is going to stick with us into the New Year like a snowbound Corona virus.  The layer of loose, rotten snow from our early December high pressure is getting harder to trigger but the potential and the consequences of triggering should be enough to keep you off steeper terrain for now.   Human triggered avalanches up to 3 feet deep remain possible,  especially where the dense slab of snow overlying weaker layers below is thinner and more easily influenced by the weight of a skier or snowmobiler.  Shallow wind slabs or soft storm slabs created by the new snow and moderate winds over the last 2 days may be triggered near ridge tops or where the most recent layer of surface hoar formed prior to the storm.  Conditions will be changing over the next 24 hours with a robust storm cycle beginning tonight in the West Central Mountains.  With a suspicious snowpack on the ground pay attention to changing conditions and expect rising avalanche hazard.

 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    In the middle of the snowpack , 2-3 feet down, exists our layer of greatest concern,  a very weak, loose layer of faceted snow that formed during the  early December high pressure.   The upper half of the snowpack has been gaining strength slowly with each storm, and is resting on this very weak layer below.  We trended from a softer slab to a dense hard slab after the 12/20-12/21 warming and rain event.  Hard slabs are much more tricky to predict and generally have much higher consequences if you do trigger them.  This layer refuses to go away and continues to show the potential to propagate when the right amount of force or load is added in pit tests. The potential to trigger this type of slab increases where the slab is thinner especially in uneven rocky terrain or if you trigger a shallow avalanche in the weaker layers above.

    On shady aspects and at higher elevations the crystals in this weak layer are more  very loose and angular. On solar aspects, this layer is  preserved under melt/freeze and rain crusts making it even more tricky to predict how it will react to loading.  In the lower elevations, the snowpack warmed, had more rain saturation and refroze which helped to strengthen this weak layer making it less of a concern.  

    In addition, new weak layers of surface hoar were buried in the last 3 days resulting in shallow, soft slab instabilities just below the new snow.  Anyone that was out in the snow yesterday probably noticed an annoying "frist" (freezing mist) caking goggles and gear alike, mostly below 7500 feet.  This thin little zipper crust should disappear with new snow added above it but should also serve as a reminder that even subtle layers can affect snow stability. 

    The incoming storm cycle beginning tonight and continuing through Monday should be enough to either overload the snowpack (think crush it and flush it) or add enough depth and to the snowpack that the problem of the persistent weak layer will be even more diffictult and less likey to be triggered by the weight of a skier or snowmobiler.

    Pay attention to changing conditions through the day and treat each slope with a degreee of suspicion, lower angle slopes are skiing and riding better right now and will offer you the widest margin of safety when it comes to shallow and deeper instabilities.  Anticipate major changes in the snowpack as heavy snowfall increases Saturday afternoon.

     

                           

     

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Our storms are beginning to feel a little like the movie Ground Hog Day.  Light accumulations and moderate winds are the theme lately.  The most recent storm has freshened up the snowpack and added another new crop of wind slabs to the upper elevation and exposed terrain throughout the West Central Mountains.  Winds earlier this week were swirling around out of the South and West, Wednesday they shifted to the North.  Look for tell tale drifts and growing cornices to see how the wind affected the slopes you are on today.  We observed small windslabs and some shallow cracking on exposed, upper elevation slopes on Wednesday and Thursday.  One thing to consider even with the wind slab problem being fairly small and manageable is the potential for a shallow wind slab to overload the weak layers deeper in the snowpack with the potential to step down and create a much larger avalanche.  Terrain management and a quick pit on the slopes you are skiing should be at the top of your route finding checklist.

Avalanche Discussion

Make sure you and all of your partners are riding or sliding with ALL of the essential avalanche equipment and are traveling cautiously.  Enjoy lower angle options right now. This is the time to AVOID slopes steeper than 30 degrees.  Its time to get out, have fun, get rad, but realize that coverage and stability should drive your decision making.  As the slab over older weak layers gains strength, uncertanty as to its breaking point increases. The slab over our weak layer of faceted, early season snow is growing in strength with the slow, incremental loading of  the last few storms but the problem below is not going away.  Pit tests continue to show a potential for triggering and propagation on this layer.  The addition of new weak layers in the upper portion of the snowpack creates a scenario where triggering a shallow slide could be the straw that overoads our weak snow camel's back allowing shallow avalanches to step down into the deeper layers below creating a large avalanche with the potential to spread out across a slope very quickly. 

Thank you to everyone that has been sending in observations this year.  These help the forecast team form a clearer picture across the forecast area. We will be updating our observation form to make your submissions even easier in the next week.

Also, resort and backcountry skiers leaving our ski areas need  to be aware that areas outside of the ski area boundary are not patrolled, have no avalanche control work being done in them and if you are injured skiing or caught in an avalanche, the ski patrol has no obligation and may not have the resources to assist you.  Backcountry rescues are subject to the direction of the Sheriff's department and Search and Rescue Teams.  Rescue could be hours away, even close to the ski area.  Self rescue is your best option and that means that everyone in your party should have the gear, understand the risk, and have the ability to provide an avalanche rescue and to perform basic life saving medical skills.  The backcountry adjacent to resorts has of the highest concentrations of avalanche incidents and fatalities every winter no matter where you  are.  Thanks to the Friends of the Payette Avalanche Center and our local resorts, you will now see beacon checkers at our backcountry gates.  This is a great reminder of the risks you face when you leave the ski area.