The Met Office has issued a severe weather warning of heavy, thundery outbreaks of rain spreading from the south on Wednesday evening and Thursday, with some places expected to see torrential downpours.
The national weather service advised the public to be "aware of the risk of localised flooding."
On its website, it said: "Heavy and possibly thundery showers will affect some western parts of the UK during Wednesday evening, with a band of persistent and often heavy rain developing across much of Northern Ireland, west and central Scotland overnight and during Thursday.
"There is the possibility of 15-20mm of rain falling within an hour in a few places whilst 20-40mm accumulates fairly widely by the end of Thursday and as much as 80mm in a few places in Scotland."
On Thursday "other areas of heavy, thundery rain will spread into southern and south-western parts of England and Wales during Thursday, with 20-25 mm of rain possible within an hour and 40 mm within 3 hours, although many places will receive much less than this."
Forecasters added that there is the possibility the warning will be extended into Friday.
Leon said: "There will be more showers on Friday, and then a steady improvement for the weekend and next week as high pressure builds over central Europe and southern Britain. Scotland is expected to be windier, with rain over the weekend and the start to next week.
"Through next week we can expect dry days with variable cloud and light winds. There is always the risk of overnight and early morning fog though. Afternoon temperatures are expected to be above average and typically 17 to 19C, so we can hold off turning the heating on for a bit longer yet."
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