"I can’t remember a time that I’ve seen more red flags in one ride. We observed widespread cracking and collapsing. Avalanches were easily triggered on any test slope steeper than 30 degrees."
Snowpro, avy educator extraordinaire,Wasatch SAR member, pro sledder, and all around great guy Tyler St. Jeor states it best in his comment from yesterday.
Here's the deal-
A persistent weak layer or what we call near surface faceted snow (NSF) is now buried two feet deep, blanketed by this weeks storm snow. The problem is... we've got an unusual, late season, strong snow on top of weak snow setup. And the weak layer is easily failing under our additional weight and will produce deep, dangerous avalanches today. Think of the NSF like a layer of dominoes with stronger snow resting on top. When your skis or track tip the first domino, it sets off a chain reaction in which all the dominoes (aka the weak layer) collapse, pulling the rug out from underneath, and the entire roof crashes down on us! Here's where it gets tricky... we don't even need to be on a steep slope, just near or connected to it (at the top, bottom, or to the side). Tip one of the dominoes over and now we're staring down the barrel of a scary avalanche!
What makes this situation tricky?
- We don't normally deal with long lasting avalanche problems like this, lingering deep into the winter. Today's avalanches act more like early and mid season slides that break on sugary snow near the ground except in this case avalanches will break in the middle of the snowpack. Avalanches may also break in areas below treeline where we don't often expect to see as many slides.
- You can trigger deep, dangerous avalanches by simply being near a steep slope but not necessarily on it.
- This weak layer is found on many slopes but not all, especially in the wind zone, where distribution is spotty and that make stability patterns tricky to get a handle on. So... you might find weak snow on one part of a slope but not the other. This means you may see people ride a slope and not trigger a slide, but the second or third person on that same slope may be the one to trigger and avalanche.
What to do? There are two options. Ride southerly facing slopes that don't have this weak layer, but the problem is they have a much thinner snowpack. Terrain facing the north half of the compass offers a deeper snowpack and cold powder, but likely have this weak layer and are unstable. In those areas, simply ride slopes less than 30 degrees in steepness with nothing steeper above you (avalanches don't happen on slopes less than 30 degrees but it takes training and practice to identify those with your eyes; otherwise, you have to measure them with an slope measuring app).
Notice the layer of granular, weak, sugary faceted snow in the photo below.