My oldest daughter was in the same size as your daughter at six months. She was in 12 month clothes for 6 months, Size 12 months for 6 months, and then spent 18 months is size 2T.
My younger daughter flew through all of the sizes, and is already wearing 4T clothes, even though she is just shy of her 3rd birthday.
I don't think you want to shop too much ahead for seasaonal clothing. Of course, things like jeans, dresses, sweaters can be worn in really any weather but the most extreme, and I would pick some of those up if they are on clearance, but I wouldn't stock up on snowsuits and parkas, since there is really no way to predict what size she'll be in in 10 months.
Old Navy always has clothing in their clearance dept. that are still in season, and there are a lot of flea markets and yard sales in the early fall where you will be able to buy winter clothing with a better idea of how big she'll be.
Once your daughter is 3 or 4, you'll be able to stock up a year ahead of time.