Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
1 · Debole
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You will be rolling the dice if you decide to step out onto steep, open slopes at mid and lower elevations where a known weak layer may be lurking.  Consider sticking to simple, lower angle terrain where you can avoid being part of the avalanche problem. If you decide to travel above treeline, keep an eye out for isolated, shallow wind slabs.

Problemi valanghivi

  • Persistent Slabs

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

    On December 8th a weak layer of surface hoar was buried by over 1’ of new snow.  Since then-  forecasters, ski patrollers, and observers have been tracking its distribution across the terrain closely.  So far, the most sightings of this layer have been below and near treeline, specifically on open slopes with minimal canopy.  

    The last known avalanche on this weak layer occurred last Sunday (Dec 11th)  when we received numerous public observations (thank you for submitting!) that reported widely propagating slab avalanches as well as snowpack test results highlighting this layer.  Most significantly, a skier was caught, carried and partially buried after being strained through trees that day. Fortunately, the skier was uninjured and self-extracted. These slab depths were up to 2 feet deep which correlates with the depth of the buried surface hoar. 

    As of Thursday (12/15), I found this weak layer in most places that I traveled in the Tilly Jane area.  A key takeaway from this field day is that this weak layer still showed the ability to propagate across a slope. In 4 out of 5 of my snowpack tests,  I received full propagation in extended column tests. Check out my observation here for more details. 

    You can locate this layer by using snowpack tests and looking for a thin gray 1-2’ below the snow surface.  If you can’t visually see this layer, using extended column tests or compression tests are a great tool to help you locate it.  This avalanche problem isn't going away quickly, so consider sticking to smaller and lower consequence terrain at these elevations. 

    (12/15/2022)

    The layer of buried surface hoar was easily identifiable along the Tilly Jane Ski Trail.  Look for a thin gray line thats 12-15 inches below the snow surface. 

    SE aspect @ 5070 ft 

     

     

    Photo: Joe Dellaporta

Avalanche Discussion

We are starting to form a better idea of where this buried surface hoar lives. Some uncertainty remains in above treeline locations where observations have been limited. It's unlikely that surface hoar survived at these locations, however, this elevation band is not hazard-free. Still keep an eye out for signs of instability, such as recent avalanche activity or cracking in the snow. 

This short dry stretch has created variable surface conditions across the zone. On slopes that face the sun, you may find a thin breakable crust. More shaded and sheltered areas are still holding preserved dry snow. With the cold and clear nights, many areas have already developed a fresh crop of surface hoar and near-surface facets. This weak surface snow will be worth tracking as we head into our next round of precipitation later this weekend. 

If you get out into the backcountry,  please submit an observation on our public observation platform!  

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