One lane is blocked after an accident on the A4232 inbound at the A48 Cowbridge Road West / A4050 Port Road (Culver House Cross).
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Any heavy showers will clear away northeastwards through late evening.
The Scarlets were comprehensively beaten 38-16 by Leinster in Dublin.
Cardiff Blues survived an onslaught from Pau's powerful pack to book a place in the European Challenge Cup final.