So far this autumn, the jet stream – which determines what sort of air mass affects the UK – has been sitting to the north.
This has allowed mild south or south-westerly winds to flow, particularly across the southern half of the British Isles.
This week, however, the jet stream will start to sink further south, allowing the winds to turn more northerly and introduce a colder air mass.
While it will feel significantly colder compared to recent weeks, especially in the south, temperatures will actually be near normal for the time of year or perhaps just a little below.
Afternoon highs on Wednesday will be around 12C to 14C in Northern Ireland and Scotland and 14C to 16C in England and Wales.