if he is an older cat or this is not his first winter with you but it has never happened before. different cats have different coat types and even short haired cats can shed sometimes a lot. this could also be related to his diet even though you did not change it recently a kitten that grows up for example can sometimes need a different diet then he used to and in a similar manner a cat that has gotten older may need a different diet. i would suggest visiting the vet, any problem with him that is causing the shedding can be checked by the vet and hopefully solve 