Northwest Mountains

The good news is that there are fewer slopes that will produce a slab avalanche today than compared to last week. The bad news is that it will be difficult to identify why one slope will avalanche today and another with similar terrain characteristics will not. The current persistent slab avalanche problem is complex and difficult to predict. Instead of attempting to outsmart the problem, focus on managing it through your terrain choices. Opt for simpler terrain where you are confident in managing uncertainties rather than more complex terrain with trigger points, convex rollers, and overlapping avalanche paths. A triggered slab avalanche will likely be large and potentially deadly.

4 long weeks! That is how long it has been since the last time we saw MODERATE avalanche danger show up in the avalanche forecast. The avalanche danger is slowly easing as a few changes occur in the snowpack. Let's look at the extreme ends of the spectrum where persistent slab avalanches have become less likely to trigger, and then those Goldilocks slopes that remain the most concerning. Where the snowpack is shallow, the cold weather has begun to facet away the slab. As those slabs break down, they are not as capable of propagating an avalanche through the terrain. Where the snowpack is deep, weak layers in the middle of the snowpack have had enough time to gain some strength, becoming less sensitive to triggering or requiring a thin trigger point to initiate a collapse. The Goldilocks slopes are likely going to be somewhere between ~90cm and ~120cm, where slabs remain intact and weak layers have not gained much strength. The total snow depth is extremely variable across the forecast area, largely due to all the avalanche activity that has occurred this winter. In general, lower-angled slopes tend to be deeper, and steep start zones tend to be shallower. Of course, elevation and location within the forecast area also play a big role in the total depth of the snowpack. 

The current persistent slab avalanche conditions are complex. There are slopes producing rolling collapses that are unlikely to produce a slab avalanche because the slab is mostly faceted away, and there are other slopes that are very much capable of producing a large slab avalanche, but they will not provide any obvious feedback about their potential instability. This winter, hundreds of avalanches have been recorded, and they have created widely varying snowpack structures from low-angled slopes to steep slopes and even one steep slope to another steep slope. So we're circling back to this travel advice of managing the avalanche problem through the complexity of your terrain choices. In more complex terrain with varying snowpack depth, trigger points, and multiple start zones, the avalanche problem will be much harder to understand and manage. In simpler terrain, it will be easier to get a feel for the snowpack structure and manage any uncertainty about where you may be more likely to trigger. 

Dry loose avalanches, or sluffs, are also becoming more common in steep terrain as the recent cold weather creates more faceted or unconsolidated snow available for entrainment. 

Events:  Our next Fireside Chat is this Thursday, 7 p.m., at the billy barr lounge, where Danielle Beamer will discuss Mental Health and Backcountry Decisions.  The event is free and open to all.