Much of the UK is currently in the midst of warm conditions for the time of year, with temperatures in excess of 30C expected in some southern areas.
Only six Septembers in the last 50 years have experienced temperatures above 30C, with three of those occurring in the last decade (2020, 2016, 2013). That warmth is no longer confined to the south as it was earlier in the week, with Scotland having a chance of hitting 28C on Wednesday.
However, the conditions are expected to change for most over the next few days, as the southwest of the UK sees the first of a front moving in from the west.
A yellow thunderstorm warning has been issued for a large part of the southwest on Wednesday, lasting from 11:00 to 21:00.
Although many areas will avoid the worst of the showers, thundery downpours are possible in the area and between 30mm and 50mm of rain could fall in less than three hours, although only a few spots are likely to see those totals.
Elsewhere in the UK, and especially in the north and east, Wednesday will remain a fine, dry day with heatwave thresholds likely to be reached in some eastern parts of England.
Those showers and thunderstorms are expected to move northeastwards across the UK, bringing more widely unsettled weather through Thursday and Friday. A further yellow weather warning for thunderstorms has been issued on Thursday for Northern Ireland, Wales and parts of northern and central England. Once again, it’s important to note there is a very low likelihood that any one location within the area will experience impacts from thunderstorms, but where the storms do occur up to 30mm of rain is possible in less than an hour which has the potential to generate some surface water flooding. There is also the possibility of very localised impacts from lightning and hail.
Met Office Deputy Chief Meteorologist Dan Harris said, “The hot and clear weather currently being experienced across large parts of the UK is forecast to break down through the middle of the week as showers and thunderstorms arrive. These will initially affect the southwest of the UK on Wednesday, before moving steadily north and developing across most areas through Thursday and Friday.
“Thunderstorm warnings have been issued across a number of areas to highlight the potential for isolated impacts, including surface water flooding of homes and businesses, disruption to transport, and very isolated damage to infrastructure from lightning or hail. The semi-random nature of showers and thunderstorms means that many places will not see any thunderstorms at all, so it’s not possible at this range to be more precise about the locations at risk, or indeed be more confident about the potential for impacts.”