NY will be the hardest to predict. If that is your first stop you can check the weather before you depart and pack accordingly, but if not, you'll have to be creative. In an effort to avoid packing your entire wardrobe, you could 1) mail your winter coat & boots on ahead, or 2) don't bring a winter coat or boots and be prepared to take a lot of taxis if it is very cold. (It could easily snow a foot in March.)
The most versatile jacket would be a windbreaker/raincoat of some kind. Second (or third) the recommendation of layers--cashmere sweaters and pashminas that do triple duty.
The most versatile jacket would be a windbreaker/raincoat of some kind. Second (or third) the recommendation of layers--cashmere sweaters and pashminas that do triple duty.