Forecasters say there is a danger of flooding in some areas and have issued yellow "be aware" alerts for southern Scotland, Glasgow and the West Coast throughout today.
The storms were expected to arrive overnight and are the product of warm and humid air moving up from France.
Thunderstorms may also generate over the UK as temperatures rise through the afternoon, before another pulse of storms is likely to move up from the continent later on.
Forecasters say that affected areas will see torrential downpours, frequent lightning, large hail and strong gusts of wind.
Paul Gundersen, chief meteorologist for the Met Office, said: "We have storms affecting parts of the UK from three separate sources, each having the potential to affect slightly different areas at different times of the day.
"This means a large area is at potential risk from these storms, as identified by the amber warning, but not everywhere will see them -some spots could see a relatively fine day.
"This alert identifies the area of risk and where the thunderstorms do form we could see localised flooding, as well as the risks that go with lightning and hail. We'd advise people to stay up to date with our latest forecasts and warnings as the situation progresses."
The risk of storms moves to the eastern part of the country tomorrow while other parts of the UK should see a generally more settled day.