The UK is entering a changeable 10-day period, with temperatures initially climbing well above average in the southeast before wetter and windier weather becomes increasingly likely.
There is the potential for a deep area of low pressure to affect the UK next week, although its development, timing and track remain uncertain.
A chilly start before temperatures rise
Following Wednesday’s heavy and thundery rain, high pressure will bring a quieter start to Thursday. Clear skies overnight will allow temperatures to fall sharply, with a touch of grass frost possible in some rural areas.
Thursday itself will be largely fine. After the chilly start, warmer and more humid air will begin to move in from the southwest, allowing temperatures to recover through the day. Cloud will increase across northwestern areas as the next weather front approaches.
Mist and fog may develop across parts of southern and southwestern Britain during Thursday night and into Friday morning.
A striking temperature contrast on Friday
A band of rain will move into Scotland and Northern Ireland on Friday before gradually extending into northern England and north Wales. Its progress remains somewhat uncertain and the rain may arrive later than currently indicated.
Some heavier rain is possible, particularly across north Wales. Western Scotland could also see a wet day when outbreaks of rain and subsequent showers are combined.
The main feature will be the sharp temperature contrast across the UK. Southern and southeastern England will be warm and humid, with temperatures potentially reaching 27°C or 28°C. These values would be well above average for late September.
Behind the weather front, fresher air will reach northwestern areas, where temperatures will be limited to the mid or high teens. As the front encounters the warm and humid air further east, it may produce some heavier rain across eastern England later on Friday.
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Rain developing during the weekend
Saturday should begin reasonably fine across much of the country. However, an Atlantic trough will interact with the weakening frontal system, causing the weather to become more active later in the weekend.
Rain will reach the northwest later on Saturday before spreading across Scotland and Northern Ireland during Sunday. Ahead of the main rain band, heavy showers could develop across parts of southern Britain. Southwest England, Wales and the West Midlands are among the areas that may see more substantial downpours, with a possibility of thunder.
The wettest parts of Northern Ireland and western Scotland could potentially receive 75 to 100mm of rain from later Saturday through Sunday. However, forecast models may change the position and intensity of the rain as the weekend approaches.
Potential for wet and windy weather next week
Attention then turns to developments over the Atlantic. Changes to the jet stream are expected to encourage one or more areas of low pressure to form during the early part of next week.
One possible outcome would bring wet and windy weather to the UK around late Monday or early Tuesday, with western areas most likely to experience heavy rain and strong winds. Eastern areas may remain somewhat drier.
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A large wind field around a deep low could also generate large waves. These may coincide with the third-highest spring tides of the year, creating the potential for coastal impacts. However, there is considerable uncertainty. Some forecast runs deepen the low rapidly, while others keep it weaker or further from the UK.
A continuing west-to-east contrast
High pressure is expected to remain influential to the east of the UK later next week. This may slow approaching weather systems and steer them northwards, maintaining a contrast between wetter western areas and generally drier conditions further east.
Temperatures should fall after Friday’s warmth, returning closer to average in many areas. Brief warmer interludes remain possible, while quieter nights could bring a renewed risk of frost. Overall, the outlook favours changeable conditions, especially in the north and west, but confidence in the timing and strength of next week’s low pressure remains limited.
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