Owen Williams gave the Scarlets an early lead, but tries from Tommy Bowe and Robbie Diack combined with Ruan Pienaar's reliable boot have left Ulster 18-3 up at half time.
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The heavy showers will ease during the first part of tonight, leaving a dry night with mist in places.
A 1950s pin-up girl from the Vale of Glamorgan has returned to the spot where she won the nation's hearts.
The band play the Liberty Stadium on Saturday night as part of their 'Everything Must Go' 20th anniversary tour.