Lolo Pass - Crystal Amphitheater

It was a very pleasant day in the backcountry near Lolo Pass with nice weather and easy travel. I found evidence of the persistent slab problem on shady, north facing slopes. Poor snowpack structure exists with a weak slab above a layer of buried surface hoar. The surface hoar was a little tricky to find, as it was not preserved on a lower angle north facing slope, but was preserved nearby on a steeper north facing slope. This is likely because the lower angle north facing slope saw enough sunshine last week to destroy it, while the steeper slope remained shaded. Currently, the slab above the surface hoar is weak, and I did not get propagation in snowpack tests. I would be more concerned in areas with a thicker and/or stiffer slab, like in wind loaded areas or higher elevations. With more snow in the forecast, conditions will likely become more sensitive as the load on the weak layers increases. Also, I observed widespread 1-2 cm new surface hoar at the snow surface on shaded slopes. If it is preserved and buried, we could have another surface hoar layer to deal with. 

On south aspects, the recent snowfall had melted down to only a couple of inches and was resting on a stout crust. On those slopes, the recent snowfall produced rollerballs and likely could have produced a small wet loose avalanche on a very steep slope. But, being confined to the recent snowfall, any wet loose would have been very small. I found some corn-like skiing in the afternoon. 

Low elevation slopes had just enough snow to get around, and avalanche conditions appeared generally stable at low elevations. 

I dug two snowpits, one on a north aspect at 6400 ft and the other on a lower angle north aspect at 6200 ft. The snowpit at 6400 ft had a layer of surface hoar buried 14" deep by a slab. 10" of the slab was new snow from Monday resting on a thin crust. Most of the slab was relatively weak and unconsolidated, and an extended column test did not produce propagation (ECTN15). The snowpit at 6200 ft had 8" of new snow from Monday, resting on a crust that had some small facets below it. The crust was thicker than in the other pit, likely from last week's sunshine impacting the lower angle slope. There was no propagation in an extended column test. Both snowpits had new surface hoar at the snow surface that grew this week.