United SFO to LHR
 

Forgive me for asking what will probably turn out to be a dumb question but:
While taking happy snaps at Heathrow on 2nd Dec, I was checking Planefinder to see what was approaching and notice UA930 from SFO was on its way but seeing the track surprised me.From SFO it seems to have flown further north than others on a similar flight (BA ex Seattle, Virgin ex SFO for example). The route took the UA flight to Norway, passing down the North Sea close to Bergen and Stavanger. Both from my own experience and from looking at other flights on the same day, I would have expected this flight to arrive over the Western Isles, over Liverpool etc. It seems the United flight may have gone 400 (or more) to the East of the usual route.
Any ideas?

Possibly a more favourable tailwind on this route than via the normal North Atlantic track system where the tracks are chosen daily to take advantage of tailwinds.

T'was indeed was a very northerly track and about 20 minutes longer than the days before and after (10 hrs vs. 9:40 ish). I've only ever been that far north once, on a Norwegian LGW-DEN and it was (as I assume this was) wind related.

Thanks for the replies. I didn't think about that, having looked at the BA & Virgin tracks.
Cheers