I can't help thinking this is part of a far wider problem and is not just confined to BBC weather forecasts. I've noticed that TV news presenters have the habit of over emphasizing "key words" in the text they are reading thus making them sound unnecessarily didactic and less than journalistically neutral. Some people may be more sensitive to this than others but many may not notice anything at all. For the latter group the over emphasis of key words may effect them at a subliminal level causing them to be subconsciously influenced by the hidden opinions loaded in the text. I've noticed regularly that people in general are unduly influence by opinions pushed on them via the so-called unbiased and journalistically neutral TV news.