I'm sure the Dep. Chief won't object to me citing him directly on his briefing issued just before midday today (the emphasis italics are his, not mine), so to avoid paraphrashing or confusing the UKMO underpinning behind the 6-15d forecast. This should speak for itself re your queries and why a return to zonal is the form horse further ahead:
"...after a quasi-meridional period in approx the day 6 to 8 day f/c period in which a filling area of low pressure moves SE’wards across UK, there is a return thereafter to the generally zonal pattern already seen for most of this winter. There are differences between models.... wrt the detail of the return to a more zonal pattern, but very little disagreement that this broadscale evolution will occur.....
Examination of Shannon Entropy f/c output from both EC and MOGREPS both have low entropy / high confidence early in the 6-10 day period and later (in the trend period), with a spike of high entropy / low confidence around days 8 or 9, relating to
the detail of the return to zonal flow."
Originally Posted by: doctormog