Sometimes, as Bob states, the - NAO simply arrives unexpectedly. Although, the Euro Control did have a solution a few days back showing a stout Davis Straits block, maybe even earlier than that. Hopefully, it becomes a reality and raises the potential of a more significant storm, very cold and longer duration, and even a HA event as previously mentioned.
MJO phase 8 seems to support a -NAO, but I believe we will not be into phase 8 until early Feb, ( depending on the model you choose )
So, assuming this NAO block is brought about by Atlantic cyclonic wave breaking and deep ULL passages. If so , does the block last longer than the transient blocks so far this season ? I mention that possibility because the progressing MJO to phase 8 could end support for a longer lasting NAO block.