The Met Office has named 44 areas across the UK that are expected to be affected by thunderstorms and heavy rain on Wednesday. Some places could see 20 to 30mm of rain in just a few hours, with cumulative totals of 40 to 60mm possible in some locations.
Widespread showers and thundery rain
The day is expected to mark the start of a "more unsettled spell" of weather, bringing showers and outbreaks of rain. These will become "increasingly widespread as warm, humid air spreads northwards across the UK", the Met Office said.
"Heavy showers and thunderstorms are likely to develop, particularly across England and Wales, with a more organised area of thundery rain approaching southwestern areas later in the day," specialists added.
"Local rainfall totals of 20 to 30mm within three to four hours are possible, while cumulative totals of 40 to 60mm may develop in some locations. Much of the uncertainty relates to where areas of thunderstorms develop, meaning rainfall amounts could vary significantly over relatively short distances."
Full list of affected areas
The Met Office has released a chart showing where the rain is predicted to hit on Wednesday. The 44 areas impacted by the large band of rain are:
England: Cumbria, Lancashire, Greater Manchester, Merseyside, Cheshire, Shropshire, Staffordshire, Herefordshire, Worcestershire, Warwickshire, West Midlands metropolitan area, Derbyshire, Nottinghamshire, Leicestershire, Northamptonshire, Gloucestershire, Wiltshire, Somerset, Dorset, Devon, Cornwall, Oxfordshire, Berkshire, Hampshire, Isle of Wight, Surrey, Sussex, Greater London, Kent.
Northern Ireland: County Antrim, County Down, County Armagh, County Fermanagh, County Tyrone, County Londonderry.
Scotland: Dumfries and Galloway, Ayrshire, Solway coast, Strathclyde and Glasgow area, Southern Uplands, Scottish Borders, Inner Hebrides, Outer Hebrides.
Wales: The whole country seems covered by precipitation.
Forecast uncertainty and advice
Met Office deputy chief forecaster, Mark Sidaway, said: "While many areas will see dry and increasingly warm conditions at the start of the week, attention is turning to the potential for heavy rain and thunderstorms from Wednesday onwards.
"As warmer and more humid air moves north across the UK, there is an increasing likelihood of some heavy rain developing. Some places could see 20 to 30mm of rain in just a few hours, while there is also the potential for higher totals where thunderstorms repeatedly affect the same locations.
"The detail of which areas will see the heaviest rainfall is still uncertain, so stay up to date with the forecast this week to keep updated on the increasing risk of impactful weather during the latter part of the week."
