Ne'er Cast a Clowt until 't May is Out

On the face of it, a strange old English expression with an obscure meaning, however it is a piece of cautionary advice. The Clowt is your heavy coat or cloak and the 'May' refers to the May blossom, the blossom of the blackthorn and hawthorn bushes. The blackthorn is well and truly in bloom but the hawthorn is not quite there yet - so the 'May' is not quite fully out, so don't put your overcoat into storage quite yet.
My grandmother always talked of the 'blackthorn winter', the last chilly blast before spring really takes hold. On the other hand, the house martins have already arrived and Cotley Hill is festooned with cowslips and Easter, which is as late as it can be, is rapidly approaching.
Time to get the walking boots on.