Heavy thundery showers are expected to cause travel disruption and flooding as the Met Office issues an amber weather warning.
The alert is in place from now until 10pm tonight and will affect large swathes of Scotland.
Flooding of homes and businesses is possible and could happen quickly, the warning reads, adding that there could cause damage to some buildings from floodwater, lightning strikes, hail or strong winds.
Where flooding or lightning strikes occur, delays and some cancellations to train and bus services are likely, spray and sudden flooding could lead to difficult driving conditions and some road closures and power cuts may occur, the warning adds.
A Met Office spokesman said: "Showers will break out widely across much of Scotland from late morning, turning heavy in the afternoon.
"While many places will miss the heaviest showers, where they do occur 20-40 mm could fall in an hour with locally 60-80 mm in a few hours.
"Showers will start to merge to longer spells of rain in the evening, but easing in intensity."