Well lets see what the Met Office has to say shall we
Heathrow Harry
The jet stream, like our weather, is subject to natural variability – that is the random nature of our weather which means it is different from one week, month or year to the next. We expect it to move around and it has moved to the south of the UK in summertime many times before in the past. It has, however, been particularly persistent in holding that position this year – hence the prolonged unsettled weather.
This could be due to natural variability – a bad run of coincidence, if you will – but scientific research is ongoing research to investigate whether other factors at play.
Source:
Met Office?s Private Briefing Document For The Environment Agency | NOT A LOT OF PEOPLE KNOW THAT