Mark Davies was one of the eyewitnesses, as water cascaded over the wall of a car park after debris blocked a culvert.
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Some locally heavy showers are possible overnight, particularly in the east, where some thundery downpours are possible.
Wayne Pivac praised Scarlets' attacking style as they secured the Guinness PRO12 title with a stunning 46-22 success against Munster.
Scarlets sealed a famous victory at the Aviva Stadium in Dublin with an emphatic 46-22 victory over Munster in the Guiness PRO12 final.