Bollettino valanghe

Small point releases and small loose snow avalanche activity will increase today on steep, sun-affected slopes. Small, relatively harmless to people, wind slabs (D1) remain possible in upper elevation wind-affected terrain. Use caution and best travel practices in steep terrain, near ridge tops, in natural catchments(like gullies or other confined terrain), and where winds have filled in old avalanches from last week, where wind slabs could be deeper in these locations. Pay attention to clues that indicate wind slab development (drifted snow, scoured or etched snow surface, hollow or slabby feeling). If you are finding these clues, find a safe travel route away from consequences such as terrain traps.  

Today's Advisory is sponsored by OnXBackcountry.  Thank You For Supporting the Payette Avalanche Center!

The high pressure/ cold temperatures we have experienced through the majority of the winter have been punctuated by warming events and 2 high elevation rain events. Wind has been consistent through the winter and we have had almost weekly refreshers of a few inches of cold, dry powder over the last few weeks.  All of these factors have built what is slowly becoming a more complex snowpack.  Throughout the last week we have been finding buried layers of facets and combinations of crust and facets overlaid by a slab of varying thickness and capped with a rain crust of varying hardness.  Some of these weak layers are showing the potential for propagation, especially where the rain crust is not as stout or not present.  Variability is often the case in the spring and this year we have a lot of variability in our local snowpack.  Snow depth is highly variable too with almost 10 feet of snow on shady, wind-protected aspects and only a couple of feet on sunny, wind-affected slopes nearby. The take-home message is that despite the fact that you are unlikely to trigger avalanches today, our snowpack has increased in complexity and should give you some reasons to consider your terrain choices.  Also, if the weather changes this weekend and into the future and we start getting substantial precipitation, avalanche conditions will be rising quickly.  Take the time to take notice of the current conditions and think about how they will change when we add some additional snow. 

For today, you can keep it pretty simple and pay attention to a couple of factors while enjoying the soft snow and easy travel conditions:

• Wind Slab:  There has been consistent wind transport through most of the last week with just enough light density snow to build drifts and pillows.  You may be able to find and trigger isolated wind slabs in some areas near ridge tops, in natural depressions, or gullies. These wind slabs are likely to be small in size but could have large consequences in steep terrain or in places with terrain traps. Pay attention to the snow as you travel into upper elevation terrain and dial back terrain selection if you encounter evidence of wind slab. Watch for deeper wind slabs to have formed where avalanches released last week. Some of these crowns and bed surfaces were up to a foot thick and winds have deposited snow since last week,  refilling these old crowns and bed surfaces.

• Loose avalanches:  As the sun peaks out today, you can expect to see loose avalanche activity increasing. Point releases on steep slopes facing the sun will shed the light density snow, especially in rocky areas or just below rocky areas that accelerate the warming of the snowpack. Yesterday we saw a few natural point releases despite the frigid temps on slopes that were getting sun.  The steep west face of Osprey Point in Ponderosa Park also produced some legitimate, low elevation wet, loose activity yesterday afternoon when the sun warmed the snowpack up.  You will see more of this type of activity throughout the day today and tomorrow as temperatures rise and the clouds depart.

• 02/14 weak layer:  There are small (0.5 mm) rounded facets below this weak layer and larger (1.0-1.5 mm) slightly less-rounded facets above this weak layer. This is likely the weak layer that failed during last week's avalanche cycle. Steep slopes that slid on this weak layer are no longer a problem (see point mentioned above though). However, there may be slopes that did not release naturally where this weak layer should still be in your mind. Snowmobilers in particular should be wary of this weak layer as it is buried about two feet deep and takes a lot of force to produce results.