Weather is one of the exempted reasons for EU261/2004, if your flight was canceled due to weather, even if you arrive more than 3 hours later than your original arrival time, you won't receive compensation.
This is not true.
We are not in the USA.
The weather situation must be truly extraordinary at the departure or arrival airport.
Some wind at Heathrow in October is certainly not extraordinary.
so it’s cancelled because the aircraft in question couldn’t land in LHR prior to doing the LHR MAD turnaround?
LHR is the hub of BA.
What happened to a plane before the actual cancelled flight, is not important.
BA obviously made a proactive decision to intervene and tackle the flow rate issues in a timely fashion.
This is considered to be a commercial decision by BA - this not extraordinary.
BA (out of commercial interests) prefers to cancel shorthaul flight before cancelling longhaul flights.