Winds through the Lowe river valley and Thompson Pass were stronger than forecasted on 12/21.  This alongside light to moderate low density snowfall has built shallow surface wind slabs.  These will be initially sensitive to human triggers up to 1 foot in depth on lee aspects above 2000′ for the Intermountain and Continental zones.  Weather was more mild in the Port of Valdez on 12/21 making the likelihood less for this avalanche problem, although it remains possible.  Asses the hazard of this avalanche problem by paying attention to what slopes are loaded, how deep and their sensitivity.  Watch for signs of instability such as shooting cracks and collapsing that would indicate a slope has the potential to produce an avalanche.

Outflow (North) winds are forecasted to gain a lot of strength overnight and may reach speeds of 70 mph at ridge tops.  The light density snow will be vaporized in areas that receive the strongest winds while more protected areas will see wind slabs building in depth.

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.