WMD: I fully concur with your request for a call BEFORE turning, but:
Quote
I had a nasty scare a few years ago when I was controlling three abreast coming up into the BIG stack for EGLL. Without warning the middle a/c turned left across the nose of the a/c to his left. Other pilots were clogging the R/T trying to get their wx avoidance requests in and it was pure luck that I managed to get an "avoiding action" call in to the other a/c.
Unquote
displays perhaps a lack of forethought on your part. Given that weather avoidance was already taking place, perhaps you should have considered modifying your technique and not committing yourself to radar headings. Give yourself some vertical separation room to cope with it rather than dropping them all at once. If they have to ladder down in the hold (wherever that may be if there is a storm over the VOR!) that is better than a TCAS RA or worse on the way in!!