Was it due to the strong winds we had yesterday?

it was after all the rain we had.

probably some of the stems got damaged in the wind/rain for it to have become like that overnight. You could try very carefully pruning the dead/damaged parts, but be very careful not to accidentally cut through the healthy bits, it's easily done! I killed a clematis once through pruning what I though was a dead stem, but turned out to be a main one!

thanks for your help

It could be the dreaded "clematis wilt."

You could cut it right down to healthy growth, below ground level if necessary.
Spray next years growth with Bordeaux mixture or benomyl.

Wilt usually affects large flowered varieties of the "jackmanii" group. this sounds drastic but it has worked for me in the past.

Take courage and good luck!