July looks set to end on a warm note for many in the UK with temperatures climbing above average and reaching the high 20Cs in the hottest areas.

The transition to warmer weather takes place this weekend and is brought about by a significant change in the Atlantic jet stream.

Scotland, England and Wales will have a fine start to Saturday with some sunshine. However, a rapidly weakening weather front will bring showers or longer spells of rain to Northern Ireland.

Through the morning, cloud will bubble up and by the afternoon showers will develop and become quite widespread across the UK. The heaviest will be in east Scotland and north-east England where there may be a rumble of thunder or two.

Maximum temperatures will reach 18 to 23C, close to the average for the time of year, and it will feel warm in any July sunshine.

The Atlantic jet stream, a zone of fast winds flowing at an altitude of about six miles (10km), makes and moves around our areas of high and low pressure.

The unsettled start to the weekend is due to a trough pattern in the jet over the UK that encourages air to rise upwards, helping showers to form.

It’s all change though for Sunday as a ridge in the jet stream encourages air to sink downwards, which builds an area of high pressure.

Many places will start the day with sunny skies, though there will probably be some low cloud with patches of mist and fog to start the day across Wales and western England – this should thin and break through the morning. The afternoon stays dry with sunny spells and a few patches of cloud.

Scotland and Northern Ireland will have temperatures widely 19 to 22C. It will be quite warm for England and Wales with temperatures reaching 21 to 25C for many.

Next week will stay on the warm side for much of the UK with temperatures a few degrees above average on the whole.

However, it is forecast to get very warm, if not hot, for central and eastern England where temperatures are expected to reach about 28C by Tuesday and could yet threaten to sneak into the low 30s.

We are then looking at the potential for some thundery rain to move up from Europe midweek and probably a return of more unsettled weather conditions to the north-west during the first week of August.

It may well be that high pressure continues to influence the weather in the south into early August with mostly dry, sunny and warm weather.

Search for your latest local forecast at BBC Weather online or on the app, or for a long-term view have a look at our monthly outlook.