aye right!

a laconic way of expressing disbelief, originally Scottish
Example He told us the forecast for the whole of April was for unseasonably warm and dry weather, and I thought ‘Aye right!’
(Note A foreshortened version of ‘aye, that’ll be right!’, which may be compared with that’ll be the day! or the more colourful tell that to the marines. Like American ‘yeah right!’, this is an idiom of the 21st century.)