Six-year-old Joshua Blackaby said he was thrilled to find out a helium balloon he set off from his primary school in Derby last December, had travelled 10,000 miles to Australia.
It was let go as part of celebrations when his school became an academy.
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Fog patches and extensive low cloud at first will steadily lift and clear.
A murky start with mist and fog then gradually clearing, although some eastern coastal districts may remain cloudier.
Isolated showers should die out through the evening to leave a dry remainder of the night.