Northwest Mountains

The primary avalanche concern remains slab avalanches releasing on weak facets near the ground, on north-facing slopes, and some high-elevation southerly slopes that held early-season snow. Near treeline is the most likely elevation to trigger one of these avalanches, and where the most dangerous conditions persist. Conditions become more variable at other elevations. If you travel in avalanche terrain today, you’ll need to carefully identify terrain features where this weak structure still exists.

With each passing day of dry weather, the areas that you are most likely to trigger an avalanche are slowly decreasing along with the avalanche danger. 

Above Treeline: The alpine is ravaged by the extreme wind event that occurred last weekend, and periods of continued strong winds this week. There isn't any snow available for continued transport. The primary wind direction has varied from west to northwest to north. Many areas are wind-eroded, or in some cases, blown back to bare ground. Other areas hold thick, hard slabs. While very few areas stayed wind-protected. Given the significant variation in snow coverage, there will be large variations in where you can and can't trigger an avalanche. Don't expect obvious feedback like you may observe at lower elevations. The most suspect areas for triggering may be the transition from thick wind-affected slabs to thinner areas.

Near Treeline: This elevation band currently holds the most likely areas to trigger a dangerous persistent slab avalanche. Trees and ridgelines do a much better job catching the snow that was blowing last weekend, and slabs remain much softer than in the alpine. The weight of a human will more easily affect the buried weak layers through these softer slabs. Observers are still noting obvious signs of instability, but those early warning signs have decreased through the week. Many avalanche paths avalanched last weekend, so expect a variable snowpack and don't be surprised by these changes. A little fresh snow is covering those old avalanches, and it can be very difficult to tell what has, or hasn't, previously avalanched. The shallow snowpack is weakening with each passing day, and over time, near-treeline conditions will become more similar to the current below-treeline conditions.

 Below Treeline: Slabs at lower elevations have lost the most strength through the week, as they slowly break down and facet. Collapses are still occurring, while cracks are having a harder time shooting across terrain features. A little wind effect can go a long way in this area,  having created slightly stronger slabs. Persistent slabs remain possible, so if you are traveling in avalanche terrain, keep your eyes open and try to identify those terrain features with heightened avalanche concerns. Once we start seeing clear nights this week, the faceting process will accelerate and break down those remaining slabs more quickly. 

The pattern of avalanche activity: This graph shows the currently documented avalanche activity since 12/6. Northeasterly facing slopes have been the most active. Northerly facing slopes held weak, sugary facets through the November drought and are most problematic. With last week’s winds often loading toward the southeast, we’ve also seen avalanches on high, southerly terrain.  Some of these upper-elevation, leeward slopes retained old snow through the drought and deserve equal caution. While much of the recent activity likely failed as wind slabs on short-lived weak layers, our late-November fieldwork shows that a collapsible crust-facet combo forms the base of the snowpack on some high southeast or west-facing slopes.  This leaves the door open for persistent slab behavior as well.