Rain and storms flood risk for the whole of Wales
Lightning and hail could disrupt power supplies later, as thunder storms sweep into Wales.
The Met Office has issued a yellow "be aware" weather warning for the whole of Wales, from 16: 00 until 23:55 BST on Tuesday.
Forecasters said it could lead to localised flooding in some places, with up to 30mm (1in) of rain in the space of an hour.
A further warning, also for the whole of Wales, is in place for Wednesday.
A yellow warning is the lowest level, rising in severity through amber to red for the most severe weather.
The Met Office said some places covered by the warning could miss showers "altogether", but where the rain falls it will be heavy, and may lead to surface water flooding.