The emergency services will be tested today during an exercise at Wylfa nuclear power station on Anglesey.
The test will check the response of all the emergency services in the event of an incident involving the transport of radioactive material.
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Sunny spells will develop but the winds will be strong, especially along the coast and over high ground. The odd light shower is likely too.
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It'll be a mainly dry but chilly night for most of us with a risk of patchy frost, fog and low cloud later.