BBC monthly outlook
The unsettled weather pattern lingers into August
Wednesday 17 July – Sunday 21 July
Turning unsettled with a wet end to the week
A wetter and more unsettled end to the week is expected across the UK, although the wettest weather is expected for Scotland and Northern Ireland. On Wednesday, rain will spread in from the west from the morning, reaching western Britain by midday and spreading into central Britain into the afternoon. Rain may be heavy in places, and the odd rumble of thunder cannot be ruled out later. It will stay wet overnight as rain continues to spread across the country, but Scotland and Northern Ireland will be drier.
On Thursday, as rain clears to the east for England, scattered heavy showers and thunderstorms are expected in the north of the UK, with a few afternoon showers likely further south. A stronger frontal system arriving Friday morning from the south west will bring widespread rain with some embedded heavy showers and thunderstorms. Local downpours are likely with some of the thunderstorms, which are expected to move through Friday afternoon and evening, lingering into Saturday morning. As the rain gradually clears to the east on Saturday, most places will turn dry and fine with a fresh westerly breeze. However, heavy showers and a few thunderstorms are expected Saturday afternoon in the south east. Sunday a weak ridge of high pressure will move overhead from the west, keeping things mostly fine and dry save for a few isolated showers in the west. These are expected to become more widespread later in the evening and overnight. Temperatures are expected to remain near average for most places, although the best of the warmth will be on Wednesday in the south.
Monday 22 July – Sunday 28 July
Wet and windy in the north; warmer in the south
The last full week of July will continue with the more unsettled trend, but there is expected to be a north-south split in the weather, with the northern half of the country tending to be wetter and windier. Meanwhile the southern half will see longer dry and warm spells between weak fronts. This is due to building high pressure in central Europe which will compete with the low pressure in the North Atlantic to govern the UK's weather. This high will also bring in some significant heat to Spain, France, and into Germany, which may occasionally reach into the south east of England.
The low pressure tracking into the UK through the week will be driven by the jet stream - which is a ribbon of fast-moving air in the upper atmosphere. There is still a great deal of uncertainty on the strength of the jet stream next week, which is leading to low confidence in the forecast. The UK sits between two rather different air masses, one cool, wet, and windy to the north, and the other hot and dry to the south. A slightly weaker jet stream would allow some of the hotter air from the French heat wave to reach into the UK, resulting in some hot afternoons later in the week. At the same time a slightly stronger jet stream will see wet and windy weather dominate the weather and reach more regularly into the south.
Monday 29 July – Sunday 11 August
Often wet and windy with a few dry and warm breaks
For the end of July and through early August, the weather pattern is expected to remain dominated by low pressure in the North Atlantic. Progressive low pressure tracks will bring outbreaks of rain and some unseasonably windy weather to most of the UK, although more often to the northern half. There will be some drier and warmer spells between fronts, and these will tend to be longer lived for the southern half of the UK, especially the south east of England. These drier spells will be broken up by some fronts which at times will seem very wet for our unusually mostly dry Augusts.
High pressure is expected to gradually build into the area from the south east after it develops over the continent. This will mean that as we head into mid-August, the weather pattern will shift to more settled, drier, and warmer weather in the south and east of the country. The timing of this has been tricky to pin down so far. There is a risk that high pressure may build in much faster, and rain and winds will be pushed off to the west and north into the second week of August, leading to a more summer-like weather pattern. The main source of long-term forecast uncertainty is the potential for tropical storms in the Atlantic and Caribbean through August, which can have a large impact on the weather patterns over the UK. Hurricane season is in full swing, and conditions are perhaps becoming more favourable for some tropical storm development as we head into August, so confidence in the forecast remains low.
We will have a better idea on whether the UK will be tapping into any heat from France for the end of July, and how long it may stick around.