Good question and the answer is that the unstable layer does remain a concern for the rest of the winter but after the upper layers adhere to each other and become more stable it becomes increasingly more difficult (we hope) to trigger/ propagate all the way down to the unstable layer. Each new storm or wind loading event has a reactivation element to the ease of triggering this layer and we see this within the avi ratings and snowpack discussions by the professionals. Like snow bridges in Glacier travel, they can become fairly trustworthy (but we rope up because we don't know for sure). Unfortunately, even with continued stabilization of the upper layers of the winter snowpack the "sleeping monster exists" and if triggered will cause a very large avalanche. As the upper layer snowpack stabilizes and becomes fairly trustworthy (snow bridge example) we move into a "low probability - very high consequence" scenario. This is a much more dangerous/deadly scenario than the high probability - low consequence scenario we often encounter where we have a reactive layer that is very easy to trigger but is only 3-4" of recent light storm snow as an example. The low consequence part of the equation is if we do trigger this layer it will not have the power, volume or depth in most cases to bury us under a huge deposit of varying densities of snow and is much less likely to kill us. The low probability - high consequence scenario can fool us into a false sense of security as the "snow bridge" over the top of "the sleeping monster" may be stable in most areas but still have many hidden triggers that remain all season and if triggered will in many or most cases have deadly consequences. This type of avalanche is like the ones you read about in Europe that run "full path" and bury villages that normally would not have snow from a slide path come within 1/2 a mile. Food for thought and something all of us should be aware of in our decision making.
