We are having similar weather here in Wisconsin. Our older mare has been shedding for weeks now and like crazy last saturday. She was itchy so I took a curry comb to her and the hair just kept coming. Today it is getting up to 60 degrees and then the end of the week cooling down again in the 30's. My thinking is if she is shedding then her body is telling her it is time so I am not going to mess with it. I am not going to go crazy brushing her, but will continue to help get the nasty hair out.
Yep most horses depending on where you live are starting to shed like crazy including mine! I have just gotten a curry after it( don't curry to much during a grooming if you're worried about to much loss of hair) then a stiff brush and then a soft brush. It sounds like a lot but only do it for about 6 to 7 minutes or less. Then once you feel it's getting to warm spend a lot of grooming time with your furminator or shedding block.