ECMWF is struggling to get a hold of the weather regimes which will be dominant into October. The chart below shows each regime (coloured bars) from a positive North Atlantic Oscillation (blue) to no regime (grey) and shows the probability of each. Notice how early on the NAO positive regimes dominate, but

I woke about the size of the trough at the end of the week in yesterdays Look Ahead video. But I want to emphasise...that's a right big trough on Friday! Here's the forecast 500hPa chart for midday Friday from the GFS, and look at the size of the 'u' shape extending south