Have you considered the other side of fashion forecasting, i.e. business forecasting? To work as an analyst you will need a quantitative degree. If you are good with numbers, this route is ideal.
Yup. Start as a researcher / analyst in a good business research company (e.g. Datamonitor), then move onto fashion after 5 years.
It's no science though, and starting in business forecasting may mean high stakes for staying there because it pays better.
Fashion forecasting requires love for fashion and gut feeling for trends. I don't say that a buisness forecaster couldn't make it in fashion forecasting, I just believe to be a really bright fashion forecaster, you need more than just forecasting classical analytical skills. So if I can recommend anything, it is to be more involved in the fashion industry than to put an emphasis on gaining some forecasting experience. Because being involved in the fashion industry will eventually lend you two crucial things you can't gain anywhere else:
1. Experience with the flow of the fashion world.
2. Networking - will evetually lead you to a position as I pointed out.
But overall, you need a well rounded education. Be curious!