Northwest Mountains

4 to 7" of snow has accumulated in the last 24 hours. While westerly winds at ridgeline elevations were gusting into the 20's and 30's mph range overnight, or up into the 40's and 50's yesterday. Backcountry travelers can expect dangerous avalanche conditions on northerly facing terrain where persistent slab avalanches can release deeply into old weak layers, and on wind-loaded terrain features. Areas with the lowest threat of human triggering an avalanche exist on wind-sheltered southerly facing terrain.

Currently, the persistent slab avalanche problem is the primary driver of the avalanche danger rating. We've seen a string of notable human involvements with buried weak layers on the northern half of the compass this week: On Wednesday, a skier was briefly caught and carried in a slab avalanche. On Monday, a large slab avalanche was triggered on Schuylkill Ridge. Last weekend, a snowboarder was caught and partially buried when he triggered an avalanche from below the slope. While we have these notable human involvements from the last week, not all observations from the northern half of the compass have reported obvious signs of instability, or an unstable snowpack. The "Sand Box Layer" of weak faceted snow was widespread on the northern half of the compass when it was buried back in February. This is now our layer of concern for persistent slab avalanches. However, the snowpack structure and slabs above that layer are variable and quite complex across our greater forecast area. The complexity in the snowpack structure comes from the variable depths of this weak layer across the forecast area, and from the previous widespread avalanche cycles. For one example, if you find a deep and strong snowpack in low-angle terrain, don't assume that the snowpack is also deep and strong on a nearby steep slope. Instead you should expect, a variable snowpack structure and a chance that you may not observe any obvious warning signs of instability. 

Riding conditions are excellent right now, around the compass, thanks to fairly continuous snow accumulations over the last week. We have yet to observe a specific pulse of snow tip the balance into a widespread avalanche cycle. Instead, we have seen incremental loading throughout this time period. Since last Friday, we have seen 2 to 4 feet of snow accumulate in the NW Mountains and around 1 to 2 feet of snow in the SE Mountains. Or since 3/5 here are the changes in SWE at a few backcountry weather stations. Schofield 2.4 SWE, Butte 1.3 SWE and Upper Taylor 1.6 SWE. Slow loading conditions like this are noteworthy, or even a little scary, as individual slopes will see the avalanche problem become reactive at different times. Versus a more obvious, single and big loading event, that quickly creates reactive avalanche problems that are more obvious across large swaths of the terrain. 

There is an impressive amount of snow available to be blown by the wind, and that has already been blown by the wind. While we are at CONSIDERABLE avalanche danger, we can't rule out the potential for natural avalanche activity on wind-loaded terrain.