You should probably contact Storm...I'm not sure that you are supposed to wash it.
I HAD to wash mine, since an animal sprayed it. It was that, or throw it away. We wash our rain-proof horse blankets in a non-detergent blanket wash made especially for protecting the rain proofing, and I buy it at the tack store. I used that on my jacket, and then hung it to dry.
But I would contact Storm before washing or cleaning it. From what I remember, you are only supposed to spot clean it with a damp sponge.