Old wind slabs formed on 12/17 have settled, gained strength and become unreactive.  Light snow began on 12/19 with 1-3 inches of accumulation while moderate north winds continued.  This is forming thin windslabs on lee aspects which has caused the top few inches of snow to become upside down.

At this point this avalanche problem does not pose a significant hazard to backcountry travelers in most locations.  Isolated areas may have received more snow with specific terrain features being loaded deeper.  Poor terrain choices, such as skiing a steep lee slope above a terrain trap would be an instance where this avalanche problem could pose a significant hazard.

Anticipate the hazard for this avalanche problem to increase as more snow becomes available for transport and deeper slabs form.  To evaluate the potential hazard of this problem,  check the depth and sensitivity of fresh/forming windslabs.

Faceted snow near the base of the snowpack has been identified in all three forecast zones. In most locations above brush line, faceted snow is capped by pencil-knife hard wind affected snow.  This has created a strong bridging affect making a person or machines weight unlikely to directly affect these layers. 

Our area received 3-4 inches of snow water equivalent over a 5 day period beginning 12/11.  This put significant stress on these weak layers.  Natural avalanches did occur, but activity was not widespread and natural avalanches were mostly confined to the storm snow.  This points to the strength of the wind hardened snow overlying the weak facets at the base of our snowpack. 

It has been five days since the last significant snowfall event and stability tests that directly target these layers have not produced propagation since.  One exception was an interior location  just north of our continental forecast zone where propagation in stability tests still existed on 12/18.

Persistent weak layers are tricky to assess and are notorious for surprising people.  As long as temperatures remain cold and our snowpack is thin, these weak layers will continue to lose strength.  It is likely that facets will reactivate in the future when stress is being applied through dramatic changes in weather such as: significant snow accumulation, rapid warming and wind loading.  Maintaining safe travel protocols such as skiing one at a time and avoiding traveling in or above terrain traps will increase your safety margin.  

 The most likely areas to trigger a persistent slab avalanche would be in steep terrain that was protected from previous strong winds that have occurred this season. This could be below brushline or in areas of terrain that are typically spared from outflows.  The Continental zone remains suspect as this area has a weaker snowpack and generally receives less wind, which would decrease the bridging affect mentioned above.