Interesting thoughts Quantum.
With the jet through the UK disconnected from the main jet powering NE, I reckon any secondary low would head betwen Iceland and the UK, flattening the ridge a bit and acting as a setback while bringing some strong winds as it battles with the ridge building from the SW.
As it is, the model fields show fairly low surface convergence along the cold front associated with ex-Cristobal in the 4-5 day timeframe, due to the circulation being fairly circular in nature; winds wrap in towards the centre and this to some extent counters the cold front convergence.
Upper level divergence can only be exploited if there's surface convergence beneath it.
If ex-Cristobal's circulation turns out to be less 'clean' than currently modelled, then a secondary low becomes possible - but this sort of correction usually occurs in the 5-7 day range, particularly with the likes of ECM.
I'm still keeping my mind open on that, though.
Originally Posted by: Quantum