Andy and I stomped around the North Slope Monday and the viddy above
illustrates our problem child, a
persistent weak layer (PWL) now buried and preserved underneath about 2 feet of snow.
Longtime guide and backcountry peak bagger extraordinaire John Mletschnig was in Millcreek recently and states... "We had numerous, booming collapses with shooting cracks 50-100' in all directions on NW-N-NE-E aspects between 9500-10500' from 3/20-3/22 near Boundary Creek Yurt. All failures were on the Buried Near Surface Facet layer down 40-60cm from the surface. In all we probably had ~20 large collapses in our travels." Adding... "In sheltered locations this seems to be most prominent. By no means would I trust anything over 30° NW-N-E. I think I can say with confidence we observed Considerable danger in our travels. In the coming days the warm temps will certainly help in the long run. In the short term, all bets are off."
Here's the setup-
We know we have stronger snow on a deceptively tricky, weak layer of snow (PWL) and that creates a suspect snow structure. In fact, it's this combo that's lead to the recent string of human triggered avalanches. Now here's where the tricky gets even trickier. Today's strong sunshine and decreased winds might help to bring the PWL out of its dormancy and back to life, further complicating the avalanche equation. Yes... there's a lot going on, so let's keep it simple.
There's a weak layer, it hasn't gone away, and we're seeing the biggest sign of unstable snow... avalanches! But, it's not like there are slides everywhere and place is coming unglued. However, in addition to recent avalanche activity there are also plenty of other red flags like collapsing and shooting cracks. So the safest approach is to assume the PWL is present on shady slopes and remains guilty until proven otherwise.
Where does this weak layer exists? The bullseye locations are basically all slopes with dry powder near and slightly below treeline today. Above treeline, the PWL is not as uniform and a little more pockety in distribution. The scary part about this situation is that this layer and it's ability to produce avalanches is variable.
How to avoid it? There are two options. (1) Ride south facing slopes where this layer doesn't exist but the riding conditions are variable. Or, (2) ride northerly facing slopes with dry powder but avoid being on or under any slopes steeper than 30 degrees.