Question about routing
I've been looking at the LGW - CUN flights over the last couple of weeks.
I have noticed that often, you might expect for aircraft to follow a similar route as other aircraft doing that route, but they have been vastly different. For example the Thomson flight yesterday took a southerly route, the BA flight took a middle-ish route and then a dog leg south and the Thomas Cook flight did a very northerly route over Greenland. This changes all the time, for example the Thomson flight today is doing a northerly route.
My question is what determines these routes if not weather? Why would they go a southerly route one day and a northerly next if the weather has not changed particularly etc etc? And is there a way to know roughly in advance which route they might take for the purposes of selecting your seat to see the 'best' views of things? Not just this route, but other routes too?